Chemistry

Quantum Mechanics

--Kinetics are reactions that overcome an activation energy (AE) --lower the activation energy, the faster the reaction --thermodynamics is related to the energy differential between reactant and product

Liquid and Solid Phases

--liquids are able to have distinctive shapes and can adapt any shape depending on the container --the stronger the intermolecular forces, the more likely the molecules exist as a solid or liquid under normal conditions --as a rule of thumb, the more polar a molecule (ex. water), the greater the dipole moment and stronger the intermolecular forces --also the larger a molecule is or size in chain, more likely it is to have strong intermolecular forces --heat capacity (C) of a substance (different substance absorb different amounts of energy ) is the added energy required to increase the temperature of a given substance --heat capacity is lost when heat is transferred away from a system --it can be solved as C=q/Delta.T or amount of energy absorbed per unit of temperature change Two types of Heat Capacity: 1. Constant Volume Heat Capacity (C.v) --> if the volume is held constant, the system cannot have PV work. this means none of the energy can escape as work done by the system and all the energy change is in the form of heat (temperature change) 3. Constant Pressure Heat Capacity (C.p) --> when the pressure is held constant, the substance is allowed to expand in volume and the energy can leave the system as PV work. Also, the substance can absorb energy with less change in temperature by releasing energy to the surroundings as work. In other words, at constant pressure, energy leaves the system as work and temperature increase is minimal to diminished This means C.p is greater than C.v when it comes to heat capacity. --although C.p > C.v, it is not that much of a difference when it comes to liquid and solid form. ex. water has a constant pressure heat capacity of 1% greater than constant volume heat capacity under temp 25C ex. for vapor under 100C or boiling point, the constant pressure heat capacity is 33% greater than C.v --the more bonds a molecule has, the more energy it can channel into bond stretching rather than into raising temperature --in other words, not all the energy transferred into the system will go into increasing temp of the compound --the energy can be absorbed in the molecule as atoms that increases molecular bond motion and stretching (type of potential energy) --remember than water has strong intermolecular bonds due to its polarity although it only has two intramolecular bonds --the hydrogen bonds are broken in order to raise kinetic energy which therefore raise temperature --heat capacity on the MCAT will always be positive meaning temperature will always increase when energy is added to a substance at constant volume or pressure --so, unless it is said otherwise, assume heat capacity of a substance is constant and does not change with temperature --greater heat capacity can help substance absorb more heat with less temperature change to non (constant) --energy is written in units of Joules and a common unit seen in context of heat transfer is calorie (cal) --1 cal is 4.184 J --on food labels, it is given as Calorie (Cal) with the capital C and 1 Cal is equal to 1000 cal or 4184 J --you can calculate energy by q=C*delta.T or q=m*c*delta.T where (c) is the specific heat capacity and not calorie --use units to help solve heat capacity problems --for instance q unit can be J*kg^-1*K^-1 or cal*g^-1*C^-1 which means to multiply by grams and degrees celsius and heat measured in calories --on the MCAT, specific heat capacity may be referred to as molar heat capacity since heat capacity can be given per mole, per volume, per gram or per any other unit --so use the equation q=mcdelta.T and if c is given as molar heat capacity, m would be in moles

Substitution Reactions: Carboxylic Acid and their Derivatives

--the derivatives of carboxylic acid is essentially with a functional group that has taken the place of -OH --the most reactive derivative or most likely to undergo nucleophilic substitution is acid halide --what makes it reactive is how stable and negative the leaving group --if the leaving group is a better nucleophile or worse leaving group, the attacking nucleophile will not be successful --instead, the unsuccessful nucleophile would fall off into solution and leave the electrophile unchanged --a bad leaving group, which acyl halide has, contains a negative charge halogen atom (fluoride F-, chloride Cl-, bromide Br-, iodide I- and astatide At-) --overall, what makes it a poor leaving group is its strong base since it makes strong bonds --it is easier to convert acyl chloride to anhydride (second to be reactive), anhydride to ester, then ester to amide --but the direction backwards is not easy so the reverse reaction is not possible Types of Acyl Derivatives: --acid halide or acyl group (R-O=C-X) can form into many kinds of acyl derivates ex. R-O=C-OH is carboxylic acid ex. R-O=C-OR is ester ex. R-O=C-NHR is amide ex. R-O=C-O-C=O-R is anhydride --types of anhydrides are acetic anhydride and butanoic propanoic anhydride --acetic anhydride has an identical construct on both side which is why the name is not repeated (like bu-) **View Flash Card** --anhydrides are used to synthesize esters and amides, but given its resonance, the leaving group is more stable than esters and amide leaving groups Reactivity: --to decrease reactivity, the acyl halide becomes these types of acyl derivatives (ex. amide, ester etc) --reactive acyl derivatives can easily be made to be less reactive but not the other way around --like an ester can turn back to, lets say, acyl chloride Hydrolysis of Amides and Esters --Hydrolysis of amides is only possible under extreme chemical conditions such as high temp or strong acidity --common type of acyl halides are acyl chloride (most reactive) and acyl bromides --they are reactive due to its electron withdrawing nature of C-Cl and its stable anion as a leaving group --a common hydrolysis is esterification which is when ROH attacks carbonyl of R-O=C-OH which substitutes its leaving groups to make R-O=C-OR + H2O --or another hydrolysis is transesterification which is when alcohol reacts with esters to switch each others alkoxy group (generally in the form of R-O) ex. [R-O=C-OR.2 + ROH] to [R-O=C-OR + RO.2-H] --alcohol and carboxylic acid involved on the MCAT is typically a nucleophilic substitution (attacked by alcohol) making an intramolecular reaction which looks more complex and structure/shape changes --intramolecular ester is called a lactone --cyclic amides can be formed in intramolecular reaction called lactams since the nitrogen group can attack the carbonyl of another amino acid which joins them together with peptide bonds --although amides are the most stable of all carboxylic acid derivatives, they are unstable in small ring sizes --when amide is under nucleophilic attack, C-N bond is stronger than C-O bond so the nitrogen does not leave and it is preserved. After, C-O becomes C=O bond that is repeatedly protonated to become the leaving group instead. **Link: https://aklectures.com/lecture/structure-and-reactions-of-carboxylic-acids/intramolecular-fischer-esterificiation

Amino and Organic Acids and Autoionization of Water

A+H3)Amphoteric--> is when a substance can be either an acid or a base depending on the environment ex. is water. it typically acts as a base since it accepts proton (HA+H2O->A+H3O) --water can also act as an acid by donating a proton (A+H2O->HA+OH) --another example is a basic amino acid which can act both an acid and a base --amino acids can carry multiple charges depending on the environment Relative Acidity of Functional Group: 1. H3C-CH3 2. H2C=CH2 3. NH3 4. H2 5. HC≡CH 6. H3C-C=O-H 7. H3C-CH2-OH 8. H2O 9. H3C-C=O-OH **from 1 to 9, the acidity strength increases** Water and Acid-Base Chemistry: --recall that the principle Le Chateller states that a stressed acid and base system at equilibrium will shift in the direction that will reduce that stress --pure water reacts with itself to form hydronium and hydroxide H2O+H2O⇌H3O+OH --this reaction is also called autoionization of water --at 25C, the equilibrium H and OH concentrations are equal at 10^-7M --this is found by using the pH equation -log(10^-7)=7 --The Effect of Adding Acid: such as the weak acid HA. in pure water, three reactions will occur simultaneously 1. HA+H2O⇌A+H3O 2. A+H2O⇌HA+OH **these reactions represent deprotonation of the acid to form conjugated base A. Conjugated base A can also be protonated by water to remake the acid** 3. H2O+H2O⇌H3O+OH --The weak acid used as a reactant will cause the reaction to shift to the product side which allows increase of H3O concentration --when weak acid is made, the reaction shifts to the reactant side causing the OH concentration to decrease --but this second reaction will have a slow rate or small decrease of OH amount --if you were to combine the first two reactions with the third reaction, it shows that H3O is significant while OH remains the same or low --therefore, for the third reaction, according to Le Chatelier principle, the equilibrium will shift toward the side of reactant to offset the stress added by hydronium ions --also, to produce high concentrations of hydronium (H3O), there should be less hydroxide (OH) and vice versa since H2O+H2O->H3O+OH --the third reaction of autoionization water will remain the same as long as the temperature remains constant --you can find the equilibrium constant by K.w=[H3O][OH] --at 25C and 1 atm, the equilibrium reaction lies to the left with K.w=10^-14 --this came from pH+pOH=pK.w (pK.w equals to 14) --another way to calculate for pK.w is by adding pK.a+pK.b --but if the pH of the solution becomes 2, the ion concentration turns to [H3O]=10^-2 mol*L-1 and [OH]=10^-12 mol*L-1 --the formula of finding the acid dissociation constant (K.a) from an acid-base reaction... ex. K.a=([H3O][A])/(HA) --this essentially finds acid dissociation constant for weak acid HA --there is also a K.b (for conjugate base A or regular base. vice versa for K.a) which is K.b=([OH][HA])/(A) --when multiplying K.a*K.b it solves for K.w which consists of cross and eliminate variables (ex. A and HA are canceled out) to make K.w=[H]*[OH] --essentially, when the equilibrium constant (K) is smaller than 1, the reaction will lie far to the side of the reactants --overall, to write a reaction it is Base (ex. NH3)or Acid (ex. NH4) + H2O forming Conjugate Acid (NH4) or Base (NH3) --larger the K.a or stronger the acid, the smaller the pK.a --strong acid is when K.a is greater than 1 or p.K.a is less than 0. this is true for base --to better understand, when a question ask for K, you look for dissociation (degree in which acid or base loses or gain a proton in solution)

Strong Acid-Weak Base Titrations vs. Weak Acid-Weak Base Titrations

Titration --> drop by drop technique mixing of an acid and base --there are two reasons why titration is performed 1. find the concentration of a substance by comparing it with the known concentration of the titrant --titrant is an acid or base that is added to the substance of unknown concentration 2. find the pK.a or pK.b, hence find K.a or K.b of an acid or base Titration of Strong Acid with Strong Base Graph: --on the y-axis is the pH of solution --on the x-axis is the volume of NaOH added --the slope begins at zero volume, pH of 2 or low value --the slope increases up not as a straight line --it essentially curves up to pH of 7 (essentially slope looks like a slight smile as in slope becomes straight vertical) --at that mid point of volume and pH, it is called the equivalence point or stoichiometric point --at this point, there are equal equivalents of acid and base in solution --essentially there is a one to one ratio between acid and base --or the equivalent point for a titration of acid with base is achieved when there are the same number of moles of each exists in solution --if the concentrations differ, the equivalence point will not be where the volumes are equal --the equivalence point at pH 7 means the titration of an acid and base are equally strong --after the equivalence point, the titration curve becomes basic meaning it curves up (like straight increase then plateau) --pH is environmental meaning when pH is low, the pKa of a specie will interpret the surrounding as protic (full of H ions) --so pKa will less likely act acidic --therefore, when pH is greater than pKa, the species interprets the environment as aprotic (few H ions) --so it more likely to act acidic Strong Acid-Weak Vase Titrations: --the graph described above is strong acid vs. strong base --this graph is different when there is a titration of a weak acid with a strong base --ex. in a base solution such as pH of 10, a weak acid (acetic acid CH3COOH) is introduced causing all of the acetic acid to be found as the conjugated base (CH3COO-) --if the weak acid like acetic acid is mixed with an acidic solution pH 1, all the acetic acid will be become the acid (CH3COOH) --for both of these cases or examples, the pKa of acetic acid remains constant at 4.75 --on a graph, if the base is stronger than the acid, the equivalence point will be above 7 --essentially, at the equivalence point, there is a molecule of strong base for every molecule of weak acid Titration of Weak Acid with Strong Base: --at equivalence point, there is 50% acid and 50% base --while the y-axis represent pH, the x-axis represent volume of base --when there is fifty fifty equal concentration of base and acid, pH is equal to pKa of weak acid (around pH of 6 almost reaching neutral) --this is known as the half equivalence point where essentially one half of the acid has been neutralized by the base or acid concentration is equal to conjugated base --this point lies midpoint on the graph and it can be seen when the solution is most buffered (solution resisting pH change even when acid or base is added) --another equivalence point is reached at pH 10 when it is 100% base --recall the Henderson-Hasselbalch pH=pKa+log([base]/[acid]) --also Ka and Kw can be used to find Kb since Kb=Kw/Ka --also Kb=([OH][HA])/[A] --you solve for OH concentration to find pOH which then can be substracted from 14 to find pH --for MCAT, it is likely that pH at the half equivalence point will be asked --Henderson-Hasselbalch equation is simply a form of equilibrium expression for Ka ex. Ka=[H](A/HA) then use -log(Ka)=-log[H]-log(A/HA) then pKa=PH-log(A/HA) Weak Acid-Weak Base Titrations: --weak acid with weak base is similar to weak acid-strong base titration --the only difference is the compressed range of pH --essentially, it is impossible to reach the extreme pH values when there is lack of strong acids or strong bases --the change in pH is not drastically different so it is difficult to identify where the equivalent point lies --but if the acid becomes stronger, equivalence point fall at a pH below 7 and vice versa --for the graph, the pH is on the y-axis while volume of NH3 for instance is added in mL --pH range may start at 3 and end up at 10 with a titration point of 7. unlike the other graphs pH goes from 2 to 12+

Enthalpy

--Enthalpy (H) is the equation rather than a description of a property --in other words, its a way to express and quantify energy --equation to use H=U+PV where U is internal energy. U may appear as E and they are used interchangeably --enthalpy is measured in units of energy or joules and it is not a conserved energy or remain constant (state function) --it is also an extensive property meaning if two identical systems are combined, the total enthalpy doubles --enthalpy depends on only temperature for an ideal gas --remember, temperature is the state of motion of molecules and zeroth law states temperature exist and can equilibrate --for the MCAT it only cares about the change in enthalpy under constant pressure Zeroth Law: expect zeroth law with ideal gas problems First Law of Thermodynamics: recall that first law is when the change in energy is the sum of heat and work --in other words, you can't take more energy out than what you put in --for a system at rest, the first law can be written as U=w+q where work (w) can either be non-PV or PV --so U=w.nonPV+w.PV+q --typically PV work reduces energy in the system when the system does work at a constant pressure and in a reversible process --this can be written as w.PV=-PV which can be used to find enthalpy --enthalpy formula H=[W.nonPV+(-PV)+q]+PV; where the equation in the bracket "[ ]" is implemented from finding U or internal energy --Enthalpy is equivalent to heat (q) when there is a closed system at rest and process is in constant pressure H=q or H=w.nonPV+q --it is true since w.nonPV only occurs when enthalpy change of a system is at rest and at constant pressure --non.PV work is mainly electrical work such as contracting muscle fibers, firing neurons, and batteries --PV work is performed when enthalpy change is the heat transfer into the system (not at rest) at constant pressure --remember constant volume and constant pressure makes U(internal energy)=H(enthalpy) and U=q --basically, for ideal gas, enthalpy and internal energy depend only on temperature meaning increased temperature is increased enthalpy Second Law of Thermodynamics: states that you cannot break even so temperature and pressure flow downhill from greater to less and net entropy (disorder) is always increasing Third Law of Thermodynamics: describes absolute zero will remain zero energy meaning energy is eternal (can't end or start) --standard state is the state of the content such as the temperature or pressure of the liquid or solid substance --the state varies with phase and other factors and expressed as different thermodynamic property values --standard enthalpies is assigned to different compounds based on the change in enthalpy when the compounds are formed from raw elements in the standard state of 25C --essentially, compound's standard enthalpy of formation (H.f) is the change in enthalpy for a reaction that creates one mole of that compound from raw elements in their standard state --compounds with standard state of 25C is usually assigned an enthalpy of 0 kJ/mol --when MCAT says standard state, assume a pressure of 1 bar (1 atm) and the temperature will probably be 25C. --the change in enthalpy from reactants to products are often referred to as the heat of reaction --in other words, it is written as H.reaction=H.products-H.reactants --standard enthalpies of formation of different molecules in (kJ/mol) are provided --one of the molecule to remember is N2(g) which has an enthalpy of 0 kJ/mol because it is more stable for the nitrogen at 1 bar and 25C --positive enthalpy change is an endothermic reaction --reaction with a negative enthalpy change is an exothermic reaction --when an enthalpy change is equal to heat, the exothermic reaction produces heat flow to the surrounding while endothermic reaction produces heat flow to the system --reactions building a large molecule from several smaller molecules is known as anabolic and it is usually endothermic ex. is photosynthesis since it requires water and CO2 to form glucose --reactions breaking a large molecule down into several smaller molecules is known as catabolic and it is usually exothermic ex. is cellular respiration since it breaks glucose into water and CO2 --either exothermic or endothermic can be spontaneous or non-spontaneous --remember breaking bonds requires energy and bond formation releases energy which are true for all kinds of bonds (covalent, non-covalent, and ionic) --typically, the MCAT may tell you the delta H for the reaction --negative delta H can be characterized as heat and heat can be measured with a calorimeter --like combustion reactions, heat is released so there is a negative delta H --another example is adding heat in order to melt something and melting must have a positive delta H --you can total up the net energy (heat) absorbed or released during a reaction by counting the number of broken bonds (require energy) and formed bonds (releases energy)

Diastereomers

--the other type of stereoisomers --it has the same molecular formula and same bond-to-bond connectivity but are not mirror images of each other and not the same compound --unlike enantiomers, diastereomer pairs differ in their physical properties and chemical properties --physical properties include rotation of plane-polarized light, melting points, boiling points, solubility and etc. --maximum number of optically active stereoisomers is related to the number of its chiral centers (2^n) where n is the number of chiral centers --also the amount of optically active stereoisomers is the sum of diastereomers and enantiomers --meso compounds typically have multiple chiral centers, it is optically inactive and considered achiral --it is achiral because if you divide the molecule in half, there are mirror images of each other and the symmetry causes chiral centers to offset each other --overall, the compound cannot rotate plane-polarized light Types of Diastereomers: 1. Epimers --> that differs in configurations at only one chiral carbon (fischer look) 2. Anomers --> cyclic that are formed when a ring closure occurs at an epimeric carbon (basically looks like the chair shape and carbon with functional group go from alpha to beta and vice versa) Link Ex: https://www.quora.com/What-are-anomers-enantiomers-and-epimers 3. Cis/trans isomers --> also known as geometric isomers and it is when each of the carbon has one hydrogen and one substituent --molecules with substituents on the same side are called cis-isomers --molecules with substituents on the opposite side is called trans-isomers Link Ex: https://chem.libretexts.org/Bookshelves/Introductory_Chemistry/Book%3A_The_Basics_of_GOB_Chemistry_(Ball_et_al.)/13%3A_Unsaturated_and_Aromatic_Hydrocarbons/13.02%3A_Cis-Trans_Isomers_(Geometric_Isomers) --cis molecules have stronger intermolecular forces than trans molecules because cis molecules have dipole moments while trans do not --with stronger intermolecular forces, higher boiling points required and creating less stability --therefore, cis and trans have different physical properties --steric hindrance occurs for cis isomers since substituent groups in the cis position may crowd each other E/Z Naming System for double bond carbon diastereomers: --Z form is when two high priority substituents are on the same side --E form is when two high priority substituents are on opposite side or in a trans position Keep Track of Isomers: Step 1. from Isomers there are constitutional isomers and stereoisomers. Step 2. from stereoisomers, there are two types which are enantiomers (mirror images) and diastereomers (non mirror images). Step 3. from diastereomers, there are configurational diastereomers and cis/trans diastereomers Overall What To Look For in Reactions for MCAT: 1. pay attention to functional groups; what are they 2. find what changed; are there any missing or new bonds, are there any new or missing functional groups 3. look at individual reactants; what are the partially negative and partially positive side of the molecule, what are the center of negative charge such as oxygen and nitrogen 4. from knowing step 3, you can determine.. --negative or nucleophilic region attacks positive or electrophilic region --polar molecules are more reactive and attack the other reactant --carbon connected to negatively center will have a partial positive charge --functional group will either donate or receive electrons

Electrochemical Cells

--tiny charge difference creates an electric potential between the phases --galvanic cell is also known as voltaic cell which is made up of multiphase series of components --this offers pathway for flow of electrons between phases --essentially, electric potential that creates a current from one phase to another --the transition from one place to another is made by conversion of chemical energy to electrical energy --all phases must conduct electricity and only one of the phases is impermeable (not allow fluid to pass through) to electrons --an example of a specie impermeable to electrons is an ionic conductor since it carries the current in the form of ions --a simple galvanic cell can be represented by letters TEIE'T' and has two electrodes (anode- and cathode+) --where T stands for terminals; conductors like metal wires --E represents electrodes; also conductors --I means the ionic conductor; often the salt bridge --galvanic cell turns chemical energy into electrical energy since it is represented as a battery --while oxidation half reaction takes place at anode, reduction half reaction takes place at the cathode --electrodes may refer to only the strip of metal or both the strip of metal and it submerged in electrolyte solution --overall, the wire is attached between the electrode where current travels from positive to negative and electrons move the opposite direction --so current and electron flow move in opposite direction --also, at those anode and cathode region are where chemistry reaction such as oxidation, reduction, dissolution or precipitation of ions occur ex. electrophoresis --> electrochemical cells like DNA is negatively charged which moves toward positive charge and the negative ions are released into solution from the anode --cell potential (E) or electromotive force (emf) is the potential difference between the terminals of galvanic cell when they are connected --by connecting the terminals, the potential difference is reduce due to resistance --but emf increases when current increases --remember that reduction is the gain of electrons, so electron flow to the cathode --also current flow is from cathode to anode which is the opposite direction of electron flow Galvanic Cell with Standard Hydrogen Electrode (SHE) --anode and cathode are submerged in HCl solution --hydrogen gas enters the anode piece that also has a platinum plate --the platinum and current catalyze the production of H+ ions in the water in the form of bubbles over the platinum plate --then electrons are carried out through the wire from the platinum plate to the silver strip --Ag+ from AgCl material representing the cathode accepts the electron and it becomes solid silver --this change allows the chloride ion to enter the aqueous solution --reaction from anode is H2(g) -> 2H+(aq) + 2e- and AgCl(s) + e- -> Ag(s) + Cl(aq) --remember the oxidation potential (E) for reaction H2->2H+ + 2e- is a value of zero --many half reaction reduction potentials can be measured using SHE and Nernst equation --there is no salt bridge in the SHE galvanic cell since both electrodes are in contact with the same solution --salt bridge is a type of liquid junction to separate the different solution and this minimizes the small potential difference affected by any other liquid junction --the difference is that salt bridge is made from an aqueous solution of KCl and this allows movement of ions between solutions without creating a strong extra potential within galvanic cell --in fact it minimize potential because the potassium (K+) moves toward cathode at the same rate of Cl- moving toward anode --this means the electrons and ions can freely move across liquid junction and electrode wires without mixing the different solutions --this cause the battery to lose its chemical potential or emf in V unit In Summary of Galvanic Cell Diagram: --the solid zinc in the anode region would get rid of their electron --then Zn2+ ions are formed and dissolved into solution --the Cu2+ ions in the cathode region takes the electrons which creates a potential difference --as a result solid Cu is formed --but the goal is to transfer electron without increasing charge difference (2e+ expelled from anode and receiving 2e+ from cathode) --the electrons travel through the copper wire with low resistance to flow --the salt bridge allows ions to move negative ions toward anode and positive ions toward cathode while preventing charge buildup --on the diagram, a vertical line represent phase separation --double vertical lines indicate a salt bridge --a dotted vertical line represent a boundary between two miscible (homogenous) liquids --comma indicate species in the same phase that are separated ex. Pt'(s)|Zn(s)|Zn2+(aq)||Cu(s)|Pt(s) Example of what it looks like: https://chemistry.stackexchange.com/questions/75741/how-does-a-salt-bridge-in-a-galvanic-cell-neutralize-each-half-cell

Electron Donating and Withdrawing Properties of Functional Groups

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Most Common Functional Groups

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Carboxylic Acids, Aldehydes, Ketones and Anhydrides

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Trend of Reactivity of Carbonyls

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Functional Group Types

1. Nucleophilic Functional Group: has a partial negative charge that attacks partial positive charge atoms or functional groups and donate electrons. Donating electrons makes nucleophiles Lewis Bases. 2. Electrophilic Functional Group: has a partial positive charge and attack electrons or get attacked by electrons from other functional group. Since it accepts electrons, electrophiles are Lewis Acids. Charges and functional groups help predict outcomes and behaviors in a reaction

Kinetic Molecular Theory

Kinetic Molecular Theory: is a model that theorized ideal gas --ideal gas lacks certain real gas characteristics Ideal Gas Four Characteristics Not Shared by Real Gas: 1. gas molecules have no size or zero molecular volume 2. gas molecules do not exert forces on one another 3. gas molecules have completely elastic collisions 4. average kinetic energy of gas molecules is proportional to the temperature of the gas 5. ideal gas obeys ideal gas law PV=nRT. you assume gases are behaving ideally unless told otherwise ex. if a gas packed into a liquid, it no longer obey the gas law --with a big space, molecules can be far apart without affecting each other --so molecule size is ignored and does not worry how much space each take up --it doesn't matter the identity of the gas when it comes to the ideal gas law --what the equation does consider is each gas boiling and condensation point --on the MCAT, when a gas is packed in a flexible container, the internal pressure is equal to the external pressure --for a rigid container, the external pressure has no effect on the internal pressure of the gas so the inside wouldn't be 1 atm like how the outside is --volume within a flexible container changes depending on the temperature, pressure, and amount of gas ex. more air forced in makes the balloon expand larger --volume of a rigid container have a fixed volume that cannot change no matter how much you raise the temperature or how much you pump gas in --keep in mind P is the pressure in atm (pressure exerted/applied by the gas on its container) while V is the volume in liters and N is the number of moles of gas --pressure and volume are inversely proportional --R is the universal gas constant (0.08206 L atm K^-1 mol^-1 or 8.314 J K^-1 mol^-1 --overall, gas will always be in thermal equilibrium with the surroundings unless stated otherwise --in a flexible container, when forcing more amount of molecules, they are closer together and the number of collisions increases meaning pressure increases --if volume increase, the molecules are spread further apart and pressure decrease --these analogies are related to Boyle's Law --when PV=constant, it means temperature can change but pressure is held constant --typically though, when temperature increase the overall speed of the molecules increase which makes them strike the container with more force and frequently --Partial Pressure is the amount of pressure contributed by a single gas in a gaseous mixture --partial pressure is essentially the total pressure of the gaseous mixture multiplied by the mole fraction of a particular gas P.a=X.a*P.total --P.a is partial pressure of a gas 'a' while X.a is the mole fraction of gas 'a' --mole fraction is the number of moles of gas 'a' over the total number of moles of gaseous mixture --the partial pressure equation can be written similar to Dalton's law such as P=X.a*P.a+X.b*P.b+X.c*P.c etc --Dalton's law states the total pressure exerted by a gaseous mixture is the sum of the partial pressure of each individual gases P.total=P1+P2+P3... --for reaction aA+bB-->cC+dD, the partial pressure equilibrium can be written as K.p=[(P.C^c)(P.D^d)]/[(P.A^a)(P.B^b)] = (products^coefficient)/(reactants^coefficient) --K.p is the partial pressure equilibrium constant --P.A and etc are the partial pressures of each gas --K.p can also be solved using formula K.p=K.c(R*T)^delta.n --K.c is the concentration equilibrium constant while delta n is the sum of the coefficients of the products minus the sum of the coefficients of the reactants

Quantum Mechanics

) ==--states that elementary particles can only gain or lose energy in discrete units --each step (discrete quanta of energy) or energy unit is very small and consistent (the same) --Bohr atom is a theory of the atom --it says the atom as a nucleus is surrounded by electrons in discrete electron shells --orbital structure of the hydrogen atom is when a single electron moves around the hydrogen nucleus on an electron shell --Pauli Exclusion Principle states that two electrons in the same atom can not have the same four quantum numbers or electron's ID number --small atoms hold charge in a concentrated way because they have fewer orbitals available to distribute --therefore, smaller atoms have more stabilized charge and more readily to bond and with greater bond strength --Heisenberg Uncertainty Principle states that it is uncertain the position, velocity and momentum (p) of an object or particle can be measured exactly especially at the same time --but the more we know about the momentum of any particle, the less we know about its position and vice versa --this uncertainty arise from (DeltaX)(DeltaP) ≥ h/2 Four Quantum: 1. First quantum number is the principle quantum number, (n). --it represents the SHELL which correspond to energy level of the electrons within that shell 2. Second quantum is the azimuthal quantum (ℓ). --it represents the electron's SUBSHELL which gives the shape (s, p, d, or f). ex. l = 0 which is the s subshell, ℓ = 1 which is the p subshell, ℓ = 2 is the d subshell while ℓ = 3 is the f subshell --s orbitals are spherical and p orbitals are dumbbell shaped 3. Third quantum is the magnetic quantum number, (mℓ) --represents a precise ORBITAL within a subshell that have different orientations; ps, py, pz which can have a value range from -ℓ to ℓ. ex. each orbital can hold 2 electrons --since there are two electrons in each orbital, the number of elements in the periods section of the periodic table is 2, 8, 18 and 32 --all the electrons will spread out among the orbitals so that there is one electron in each orbital in a subshell before any has two --to solve the number of total orbitals within a shell, remember it is equal to n^2, so 1, 4, 9, 16 etc 4. Fourth quantum is the electron SPIN (up and down movement) and the quantum number is symbolized as m2 --this final quantum number is used to distinguish between two electrons that may occupy the same orbital and have the same first three quantum numbers --possible values of one spin +1/2 and the other spin is +1/2

Also Comparison of Acidic Properties of Alcohols

**See page and write on Flash Card**

Energy Level of Electrons

--Aufbau Principle, sometimes called building up principle, states new electrons or protons added helps maintain neutrality and they occupy the lowest energy level available --so with the lower energy state of a system, the more stable it is --the orbital with the lowest energy will be located in the subshell with the lowest energy ex. added electron of F is in shell 2 while electrons added of Ag is in shell 4 --for MCAT, be familiar with the shape of the orbitals in the s- and p-subshell because there is a 90% chance of finding electron somewhere inside the given shape --the way the periodic table is organized can indicate where each type of subshell (orbital shape) is filling ex. s- subshells are filled in groups 1 and 2, p- subshells are filled in groups 13-18, d- subshells filled in group 3-12 and f-subshells are filled in lanthanide and actinide series --valence electrons are located in the outmost shell of an atom --in most cases, electrons from s and p subshells are considered valence electrons --remember, total number of electrons in electron configuration is equal to total number of electron in the atom --key tips of electron configuration is that half-filled and filled subshells offer greater stability --ex. elements like in group 6 and 11 will try to achieve half-filled or nearly filled d subshell by borrowing one electron from the highest s subshell so it can produce half-filled s subshell and half filled or filled d subshell --remember elements Cr and Cu on the MCAT just in case --these elements have only one electron in the 4 s orbital --the electron configuration of Cr is [Ar] 4s^1 3d^5 and Cu is [Ar] 4s^1 3d^10 --work is the transfer of energy into or out of a system --so when an electron is added to a system, work is being done and increased electrostatic potential energy --electron configuration helps list the shells and subshells of an element's electrons in order from lowest to highest energy level --it basically indicate number of electrons in specific subshell --it can be written as Na=1s^2 2s^2 2p^6 3s^1 or Na=[Ne} 3s^1 which is representing atoms of electrons at the lowest energy level or ground state --but in excited state, it will be Na^1=1s^2 2s^2 2p^6 or [Ne] Understand Electron Configuration on Periodic Table: Row 1, 2 and He --> s orbital Row 3-8 --> p orbital Row in the center from element Sc to Zn --> d orbital Row of elements at the end and extracted out Ce to Lr --> f orbital **from top to bottom its counted from 1 to 7** **only exception is row in the center is from 3-6 and row of elements extracted is from 4-5**

Reactions and Stoichiometry

--Be familiar with the SI Base UNITS Mass: Kilogram (kg) Length: Meter (m) Time: Second (s) Electric Current: Ampere (A) Temperature: Kelvin (K) Luminous intensity: Candela (cd) Amount of Substance: mole (mol) --SI system also employs standard PREFIXES for each unit Mega: 10^6 (M) Kilo: 10^3 (k) Deci: 10^-1 (d) Centi: 10^-2 (c) Milli: 10^-3 (m) Micro: 10^-6 (u) Nano: 10^-9 (n) Pico: 10^-12 (p) Femto: 10^-15 (f) --A compound is a substance made from two or more elements in fixed proportions --Empirical formula gives the simplest ratio of elements present in a compound but not the actual numbers of atoms found in the molecule ex. glucose empirical formula is CH2O this shows 2 moles of hydrogen for every mole of carbon and oxygen --Molecular formula gives the actual number of each different atom present in a molecule ex. glucose is C6H12O6 Percent composition by Mass can be calculated by..... (molecular weight of an element)/(molecular weight of compound) ex. find the percent mass of carbon in glucose --this means glucose is #% carbon by mass Empirical Formula of a Compound.... ex. 6% hydrogen and 94% oxygen and find H?O? 1. assume a 100 gram sample 2. based on the periodic table, hydrogen as an atomic weight of 1 g/mol (found top left corner small number) 3. Oxygen has an atomic weight of about 16 g/mole 4. (6 g hydrogen)/(1 g/mol) = 6 moles 5. (94 g oxygen)/(16 g/mol) = 5.9 moles 6. Then divide both moles by the smallest of the results so... H --> 6/5.9 = 1 O --> 5.9/5.9 = 1 basically HO or H1O1 7. If the mol is not a whole number, then multiply both atom moles by 2. ex. Fe1O1.5 to Fe2O3

Bonding and Reactions of Biological Molecules: Nucleic Acids

--Nucleic acid has phosphate group that behave similarly to carboxylic acid since P=O structure is similar to C=O --nucleic acids form a chain by having one of the OG group create anhydride bonds with the phosphate group of another --this is known as phosphodiester bonds --specifically, oxygen attached to the 3' carbon of one nucleotide attacks the phosphate group attached to the 5' carbon of another nucleotide --the hydroxyl group(R or C-O-H) acts as a leaving group making the reaction a nucleophilic substitution --remember reactions between carbonyls usually involve dehydration or hydration

Observed Rotation

--absolute configuration of the molecules do not indicate the direction in which each configuration rotates the light --remember that light is made up of electromagnetic waves --changes of electric field and changes in magnetic field for a single photon are perpendicular to each other on a graph --but both magnetic and electric fields move in the same direction of propagation on a graph --a typical light source releases millions of photons whose fields are oriented in random directions --Plane-Polarized Light is when light consists of photons with electric fields oriented in the same direction --for the MCAT, understand the orientation change of the electric field produced by a photon when photon reflects off a molecule --for instance, enantiomer molecules rotates the electric field to the same degree but in the opposite direction --Optically Inactive is when no single molecular orientation is favored and the net result is no rotation of the plane of electromagnetic field --optically inactive compounds may be compounds without chiral centers or molecules with internal mirror planes --Essentially, when a plane-polarized is projected through a chiral compound, the orientation of its electromagnetic field is rotated --if the compound rotates plane-polarized light clockwise, it will have a '+' or 'd' for dextrorotary --if the electromagnetic field rotates counterclockwise, it will have a '+' or 'l' for levorotary --Specific rotation is a form of observed rotation that is calculated from the observed rotation (direction & number of degree electromagnetic field rotation) and experimental parameters --the equation consists of length of polarimeter, concentration of the solution, temperature and type of wavelength of light used --Racemic mixture is when enantiomers are mixed together in equal concentration --when enantiomers are mixed in unequal concentrations, light is rotated in the same direction as it would be in a pure sample of the enantiomer but only to a fraction of the degree --measure the optical purity by dividing the actual rotation to the rotation of pure sample --keep in mind that enantiomers have the same chemical and physical characteristics except for two cases: 1. interactions with other chiral compounds 2. interactions with polarized light

Addition Reactions: Aldehydes and Ketones

--aldehydes and ketones are the two most reactive carbonyls --only acyl chloride is more reactive than aldehyde --unlike Cl-, the -H and -C of the aldehyde and ketone does not donate electron density to partially positive carbonyl carbon --recall that negative charge atoms mean it has too much electrons so it needs to give it away --aldehydes and ketones do not have leaving group, only C-H or C-C bonds --without a leaving group, the molecule only undergo addition reactions to carbonyl carbon rather than substitution --overall, just keep in mind that aldehydes have a terminal hydrogen next to the carbonyl carbon

The Attackers: Nucleophiles

--all nucleophiles are lewis bases meaning it donate electrons --nucleophile also attacks a molecule to form a new chemical bond ex. when alcohols attack the carbonyl carbon, they form an ester (R-C=O-O-R) --recall that electronegativity is the tendency of an atom to keep or hold on to electrons close to its nucleus --nucleophilicity is the tendency of an atom to share its electrons making it opposite of electronegativity --increased nucleophilicity is decreased electronegativity --remember carbon is always partially positive making the other atoms bonded to it more electronegative ex. oxygen is more electronegative so it is nucleophilic and the bond with carbon is weaker and more polar EX. RO- is a nucleophilic molecule that attacks the carbon of C=O. from the carbon, it transfers electrons from the double bond to the oxygen which converts the double bond to a single bond and leaves another electron pair on the oxygen (O-). so the oxygen becomes electronegative or nucleophilic EX. but if the reaction contains an acidic proton.. RO- attacks the hydrogen of C-O-H which transfers the electron to the oxygen landing an extra lone pair and creating oxygen (O-). RO protonates the hydrogen to develop ROH. --remember, nucleophiles will always attack a carbon atom --when a carbon is attacked, it must give up a pre-existing bond to make room for the new bond --Leaving Group is when a portion of the molecule leaves. a good leaving groups are atoms with a greater number of electron shells which are able to distribute their charges --stable leaving groups such as gases (CO2 and N2) leave the solutions and do not return which means they do not compete with other nucleophiles since good leaving groups are bad nucleophiles --essentially a nucleophile that attacks a molecule containing a weaker nucleophile will act as a leaving group --so it is important to know which nucleophile in the reaction is the strongest Ex. nitrogen is more nucleophilic than oxygen so oxygen will be the leaving group and nitrogen will bond --the best nucleophiles are strong bases and the worst leaving group and vice versa (weak bases) --strong bases typically have hydroxide (OH) and atoms from the first and second group

Bonding and Reactions of Biological Molecules: Proteins and Amino Acids

--amino acids consists of amine and carboxylic acid functional group attached to the central carbon --the amine of one amino acid acts as a nucleophile to attack the carbonyl of the carboxylic acid of another amino acid --this forms an amide bond or peptide bond --alcohol is then a leaving group and this reaction is a classic nucleophile substitution reaction --the structure is made up of an H bond and R group (and two other groups) attached to the central carbon --R group uniqueness is what gives amino acid its biochemical properties and its stereochemistry (r and s) Link of ex: http://www.astrochem.org/sci/Amino_Acids.php --amino acid found in the body are referred to as L amino acids Gabriel Synthesis: --begins with a potassium phthalimide containing a nitrogen --the nitrogen acts as a nucleophile and attacks diethyl bromomalonate --diethyl bromomalonate has a bromide connected to the central carbon which is what gets attacked --bromide is protonated and substituted --the rest of the diethyl bromomalonate structure essentially lost bromide and is attached to the nitrogen of potassium phthalimide --the carbon becomes nucleophilic since it now has a negative charge (lost hydrogen) and undergoes another nucleophilic substitution with a new alkyl halide --in other words, an R group is added to the amino acid at the negative carbon --the nitrogen (connected to the carbon and R group) is hydrolyzed from phthalimide by acid and water to form the original free amino acid molecule **overall, this is an important reaction since it is what helps us survive** Strecker Synthesis: --an aldehyde (R-C=O-H) is mixed with potassium cyanide (KCN or HCN) and ammonium chloride (NH4Cl) --cyanide anion (CN-) acts as a nucleophile toward carbonyl --eventually the nitrogen becomes the next nucleophile instead of oxygen --acid is present to protonate the alcohol group --nucleophile substitution occurs and aminonitrile is formed (from R-C=O-H to NH2-C-R-H-C-N) --all those groups are connected to carbon --next, aminonitrile is exposed to strong acid in water (H+/H2O) which protonates the nitrile group --which substitute from C-N to C-OOH making the original amino acid NH2-C-R-H-COOH

Nucleophilic Addition to Aldehydes and Ketones

--both aldehydes and ketones are carbonyls without a good leaving group --meaning these molecules cant accept substitutions or undergo substitution reactions --instead, the electrons connected to the carbonyl carbon moves to the oxygen as a lone pair --this allows room for nucleophiles to attack the molecules --Aldehyde is a carbonyl=O and the carbon is attached to C and H --Ketone is carbonyl=O and carbon connected to two carbons (ex. 2 of CH3) Nucleophile Reaction: Step 1--> nucleophile attacks carbonyl carbon Step 2--> carbon releases pi bond electrons to oxygen turning the entire molecule to alkoxide anion Step 3-->negatively charged oxygen of the alkoxide anion may or may not get protonated depending on the environmental acidity. if it does get protonated, the molecule becomes an alcohol Step 4--> carbonyl carbon will remain to have four bonds. Two bonds to either carbons or hydrogens plus connected to one nucleophile and one to oxygen Step 5--> the bond to nucleophile can switch alkoxide or alcohol back to its initial carbonyl form. common nucleophiles in this reaction are alcohols, amines, hydrides, nitrile and organometallic reagents. Hemiacetals vs. Acetals: --if the nucleophile is an alcohol, it can cause aldehydes and ketones to form hemiacetals --hemiacetals consists of a bond to OH group as well as a bond to an OR group off of carbonyl carbon --hemiacetals can be formed either basic or acidic conditions --it is often unstable to be isolated unless they exists as a ring structure --if there are additional ROH group as nucleophile, OR group is added while replacing OH group and this makes acetal or ketals --unlike hemiacetals, acetals are not easily returned to their carbonyl form because OR groups are hard to be broken to allow the return of C=O. --the fact OR groups are difficult to break, acetals and ketals are great protecting groups --aldehydes and ketones may temporarily change into acetal in order to prevent nucleophile reaction --this is necessary since aldehydes and ketones are relatively reactive --in order to form an acetal from hemiacetal, hydroxyl group must be protonated to make a good leaving group (water) which gives it the opportunity to be catalyzed by acidic conditions --to stop the transformation at the hemi form, there needs to be a base-catalyzed condition --example of hemiacetals are carbohydrates Amines: --aldehydes and ketones that reacts with amines will form imines and enamines --imines has a carbonyl that is double bonded to nitrogen (C=N) --enamine consist of alkene (C=C) and an amine substituent (N-R) --enamines may be more stable than enols, but it is relatively not stable because the nitrogen is electron withdrawing --tip to know if reaction will form imine instead of enamine is that original amine that has one R or no R group will likely make imine (C=N) --if the original amine has two R groups, the N cannot afford a double bond to carbonyl, so it will make enamine. --keep in mind that organometallic reagents are just R- while hydride ions are H-. --organometallic reagents are strongly basic and potent nucleophiles --most common reaction for organometallic compound is nucleophilic attack on aldehyde and ketone to produce an alcohol after an acid is added --Hydride to synthesize alcohol is called reduction synthesis --reaction consists of H- react with carbonyl and prevents the carbon skeleton to extend like how organometallic reagents does --hydride reagents reduce aldehydes and ketones by donating H- --hydride reagents are sodium borohydride (NaBH4) and lithium aluminum hydride (LiAlH4) **View page of examples of how nucleophilic reactions occur between acidic vs. basic conditions**

Substitution Reactions: Carboxylic Acids Nomenclature and Physical Properties

--carboxylic acid consist of carbonyl with an alcohol group --it typically act as acids (losing a proton from -OH, specifically the hydroxyl group to make a better leaving group which forms into water -HOH) --or as substrates (attacked by nucleophiles) --a common group of carboxyl acid are aliphatic acid which have an R group to the alkyl group (O=C-OH) --when a carboxylic acid are connected to hydrogen bonds, it is strengthen to form dimers --dimers are what increases boiling point of carboxylic acids by increasing molecular weight and leaving the liquid phase --saturated carboxylic acids are an example of generally solids since they have more numbers of carbons --an unsaturated carboxylic acid will have double bonds which impede the solid and lowers the melting point --carboxylic acids, therefore, will the least number of carbon are miscible/likely to form with water --more number of carbons make it insoluble in water and they are very strong compared to other organic acids since it can be protonated and proton is removed to stabilize --basically the electron withdrawing group on the carbon help further stabilize it by increasing the acidity --but most carboxylic acid are soluble in most nonpolar solvents

Accounting for Energy: Hess' Law

--change in enthalpy only depends on the identities and thermodynamic states of the initial and final compounds --Hess's Law of Heat Summation states the sum of the enthalpy changes for each step is equal to the total enthalpy change regardless of the path chosen EX... Step 1: N2+O2-->2NO with H=180 kJ Step 2: 2NO+O2-->2NO2 with H=-112 kJ Result Reaction: N2+2O2-->2NO2 with H=68 kJ --for each step reaction, on a graph the y-axis is labeled as enthalpy, Gibbs free energy, or simply energy --the x-axis is the reaction progress from reactants (from the left) to products (to the right side) --the graph shows enthalpy change in the forward and reverse direction using the same amount of energy in the reverse way --increase in energy is called activation energy which affects the rate, or kinetics --peak of the energy hill represent the transition state where old bonds break and new bonds form --whether the reactants overcome a high activation energy or low activation energy makes no difference to the final change in energy especially since the energy between products and reactants is constant Example of Graph in Link: https://socratic.org/questions/55802401581e2a75defa5da3 --for the MCAT, remember that a catalyst affects the rate of a reaction but not the overall change in energy which are expressed as H, G, or S --typically, a catalyst lowers the activation energy and activation energies of the forward and reverse reactions are lowered by different amounts Summarize Laws of Thermodynamics: 0th Law --> two bodies are in thermal equilibrium with the third body so they are all in equilibrium with each other A=B=C. This means temperature exists and is a state function. temperature is thermal energy per mole while pressure is thermal energy per volume 1st Law --> energy of an isolated system is conserved for any reaction 2nd Law --> entropy of an isolated system will never decrease. but entropy can increase with temperature, volume, and number 3rd Law --> pure element or perfect crystal at zero Kelvin is assigned an entropy value of zero. other substances at other temperatures have a positive entropy value **overall, heat and work are able to change the internal energy of a system** **enthalpy (H) as U+PV while entropy is he spread of energy outward**

Concentration Cells and Electrolytic Cells

--concentration cell is the limited form of a galvanic cell since it is never at standard conditions --so Nernst equation must be used to solve cell potential --concentration cell is basically another type of galvanic cell --essentially the reduction half reaction takes place in one half cell and the reverse half reaction takes place in the other half cell example of what it looks like: https://commons.wikimedia.org/wiki/File:Cell_5.jpg --if the concentration on both sides are equal, the cell potential would be zero --remember the Nernst equation can be used to calculate the potential for a concentration cell E=E.not-RT/nF(logQ) --MCAT is more likely to ask qualitative questions such as "in which direction will current flow in the concentration cell" --remember electrons flow in the direction that allows concentration in the half cells to become equal --so it will flow toward the side that has greater concentration of positive ions so the current flows the opposite way How to Tackle Nernst Equation: --usually known that standard temperature is 25C or 298K --also given is 0.01M in the half cell with anode and 0.1M in the half cell with cathode --2e- travels through the wire between electrodes --so plug the ratio and number of moles of electrons in so it looks E=E.not-(0.06/2)ln(0.01/0.1) --E.not is equal to zero since it is the value when we add two half reactions Electrolytic Cell: --it is another type of cells besides galvanic cell --it is created by hooking up a power source across the resistance of a galvanic cell --this forces all the reactions to run in reverse --on the MCAT, electrolytic cell will have a negative emf --also the cathode is marked negative and anode is marked positive --reduction still takes place at cathode and oxidation at the anode --this kind of cells are used for metal plating and for purifying metals (Cu) ex. pure sodium can be collected from sodium chloride solution --the reaction will not be run in aqueous solution because water has less negative reduction potential than sodium (Na+ + e- --> Na) with E=-2.71 V while water (H2O+2e- --> H2+2OH-) with E=-0.83V --this means sodium will oxidize spontaneously in water and stronger reducing agent --Key take is that galvanic cell have a positive cell potential while electrolyte cell has a negative potential --while galvanic cell is spontaneous using E.max in voltage, electrolytic cell requires force by an outside power source so using current --electrochemical cell means it can either galvanic or electrolytic cell

Paramagnetic and Diamagnetic Elements

--consider that similar charges repel each other --the mutual repulsion creates an increase in potential energy --this is the case when the electrons avoid sharing an orbital and instead spread out amongst the orbitals of a given subshell --electrons are represented by vertical arrows --upward arrows indicate positive spin --downward arrows mean negative spin --according to Hund's rule, the electron prefers to have its own orbital (s, p, d and f) --paramagnetic elements are elements with unpaired electrons, meaning a subshell is not completely filled --the spin of each unpaired electron is parallel to the other electrons, creating external magnetic field --Diamagnetic elements are elements with paired electrons, meaning the subshells are completely filled and making them unresponsive to external magnetic field --paired electrons have both upward and downward arrows in the same orbital of a subshell while unpaired has only one arrow (most likely up only)

Potentials

--electric potential (E) is associated with any redox reaction --when the potential is positive, the more likely the redox reaction is to proceed --to find the oxidation potential for reverse half reaction, the sign of half reaction potentials (reduction potentials) is flipped --each component is called a half reaction and any reduction half reaction is accompanied by an oxidation half reaction --there is only one possible potential for any given half reaction --half reaction potentials are usually listed as reduction potentials Standard Reduction Potentials at 25C: --on the left side of the table are half reactions --the reactions starting from the bottom contains 2e- and moves up containing more electrons (ex. 4e- and 3e-) --from bottom to top of the table, the reactants in this direction are stronger oxidizing agents and more easily reduced --on the very right side are potential (E) --from top to bottom, the values range from 1.50 to -0.83 as an example --products in this direction are stronger reducing agents meaning easily oxidized --water is both the poorest oxidizing agent and reducing agent --with a high positive potential, the half reaction is able to be involved or part of the final reaction in aerobic respiration --it is because oxygen accepts electrons to form water --the only reduction potential that needs to be memorized is 2H+ + 2e- --> H2 with E=0.00 V or electric potential has no absolute value ex. 2Au3+ + 3Cu --> 3Cu2+ + 2Au --you can solve for potential value (E) of this reaction by first separate the reaction into two half reactions 2(Au3+ + 3e- ==> Au) -> E=1.50V 3(Cu ==> Cu2+ + 2e-) -> E=-0.34V --then add up the half reaction potentials. the potentials are given in the table. --Cu=>Cu2+ + 2e- is a flipped reaction (product to reactant) so E is negative --the two potentials are added (1.50 + -0.34 = 1.16V)

Elements and the Periodic Table

--elements are the building blocks of compounds and cannot be decomposed into simpler substance by chemical means --each atom can be identified as belonging to a certain element --ex. Carbon on the periodic table has an elemental symbol of C. Mass number of 12 which the sum of protons and neutrons. Atomic number of 6 which is the amount of protons --since each element has a unique number of protons, atomic number provides identity of element --an element may have any number of neutrons or electrons, but only one number of protons --mass number of an element is roughly equal to its atomic weight or molar mass --atomic weight is commonly abbreviated as amu or grams/mole --but not ever element will have a mass equal to mass number (proton + neutron) --atomic weight is the weighted average of the isotopes of that element --isotopes are two or more atoms of the same element that contains different number of neutrons --ex. hydrogen has 3 important isotopes; 1^H (protium), 2^H (deuterium), and 3^H (tritium) --also carbon has isotopes 12^C, 13^C and 14^C --each of the carbon's isotopes contain 6 protons with varying numbers of neutrons --ion is defined as number of electrons in an atom that does not equal the number of protons, this cause the atom to carry a charge --salt is a neutral compound composed of a positive (cations) and negative (anions) ion --ions are important to regulate cellular activities, such as action potential in neuron --when a neutral atom loses an electron to become a cation, it gets smaller --this means there are more protons than electrons --this result to positive charge of the nucleus exerting a greater attractive force on each valence electron --this then cause electrons pulled closer to the nucleus --loss of an electron also reduces repulsive forces between the electrons --vice versa for gaining electrons, greater repulsion and greater in size

Characteristics Within Groups

--elements in the same group on the periodic table have similar chemical properties because they have the same number of valence electrons --this means they have the same number of bonds and similar charged ions --Memorize; alkali metal in group 1 or IA, alkaline earth metal in group 2 or IIA, oxygen group 16 or VIA, halogen group 17 or VIIA and noble gases in group 18 or VIIIA --Group 1 alkali metals are soft metallic solids with low densities and low melting pointing --Alkali metals easily form 1+ cations like NA+ which makes them highly reactive with most nonmetals to form ionic compounds --examples of ionic compounds are hydrides NaH --Group 2 alkaline earth metals are more solid/harder, more dense and melt at a higher temperature --they typically form 2+ cations such as Mg2+ --it is less reactive because its highest energy electron completes the s-orbital --but, between alkaline metals, heavier ones are more reactive than lighter ones --while group 14 form four covalent bonds with nonmetals, group 15 can form 3 covalent bonds --group 16 elements are known as chalcogens or oxygen group --oxygen and sulfur are important chalcogens for the MCAT --oxygen can form strong pie bonds to make double bonds since it is second most electronegative element --oxygen (O2) reacts with metals to form metal oxides (O3) --sulfur can form 2, 3, 4, 5, or even 6 bonds --it has the ability to form strong double bonds --most common form of pure sulfure is yellow solid S.g. --most common form of sulur found in nature is metal sulfides Na2S --Group 17 element is known as halogens and they are fluorine, chlorine, bromine and iodine --halogens are highly reactive since they like to gain an electron to attain noble gas configeration --sometimes halogens can also bond to other highly electronegative atoms such as oxygen to take on oxidation state --halogens can also combine with hydrogen to form gaseous hydrogen halides which are soluble in water and form hydrohalic acids --halogens react with metals to form ionic halides like NaCl --Group 18 are noble gases and also known as inert gases --these are nonreactive and known in nature as isolated atoms --they are gases at room temperature, overall noble gases are very stable which is why elements tend to try to form this state --it is safe to assume that elements hydrogen, oxygen, nitrogen and halogens are in diatomic form unless states otherwise --ex. nitrogen is nonreactive meaning N2 rather than N

Reversibility

--entropy is a state function so the reaction runs exactly in reverse and able to return to its original state --but the entropy in the system cannot decrease for any reaction --reactions in equilibrium or moving forward and reverse directions must have an entropy change of zero in both ways --but in real world, reversible reactions do not happen --but if we imagine in hypothetically, the system and surroundings are at equilibrium meaning transfer of heat can occur when the system and the surroundings are at the same temperature --equilibrium can also mean that the rate of forward reaction equals the rate of reverse reaction --this is the point of achieving maximum universal entropy for the reaction since S.universe=S.surrounding+S.system --entropy change can be determined a similar way as enthalpy(H) since both are state function H.reaction=H.product-H.reactants S.reaction=S.product=S.reactants

Vapor Pressure

--equilibrium occurs when rate at which molecules leave the liquid equals the rate at which molecules re-enter the liquid --partial pressure created by gas or molecules in the open space (above or with the liquid moles in the same container) at equilibrium is called vapor pressure of the liquid --when water is evaporating, this means the number of molecules leaving the puddle is greater than the number of water molecules entering the puddle --when the air is moist, this means the air also contains water molecule making partial pressure of water vapor greater than the vapor pressure --therefore, water would condense into the puddle --instead of comparing partial pressure in the puddle with vapor pressure, you can also compare vapor pressure and atmospheric pressure --atmospheric pressure is the sum of all the partial pressures in the air above the liquid --when vapor pressure of liquid is equal to atmospheric pressure, the liquid boils --solids also have a vapor pressure which can be equal to the vapor pressure of the liquid phase which makes a melting point --solute without a vapor pressure is known as nonvolatile solute --when nonvolatile solute is added to a liquid, some solute molecules will reach the surface of the solution allowing reduced surface area for liquid molecules --solute molecules that do not break free from the solution will still take up surface area --while the number of molecules breaking free from liquid decrease, the surface area and volume of open space above the solution remain the same --you can solve for vapor pressure of the solution (P.v) or vapor pressure of pure liquid (P.a) by P.v=X.a*P.a and X.a is the mole fraction of the liquid. this equation is known as Raoult's Law --for a situation using volatile solute (solute with vapor pressure), you can calculate for the total vapor pressure of the solution by using the sum of partial vapor pressure P.v=X.a*P.a+X.b*P.b

K: Reaction Quotient

--if a reaction is at equilibrium, plug the concentrations of the products and reactants into equilibrium expressions which gives the equilibrium constant --when the equilibrium is disturbed, substitute variable Q for equilibrium constant K --Q is the reaction quotient that is not at equilibrium Q=(products coefficient)/(reactants coefficient) --when Q change to become closer to K, this means reaction is moving toward equilibrium --so we compare Q and K in order to determine the direction the reaction is proceeding --Q equal to K indicate reaction reaches equilibrium (remember on a graph it is the highest peak of a frown curve or greatest entropy) --Q greater than K indicate ratio of product concentration to reactant concentration is greater than ratio at equilibrium --this means reaction shift to increase reactants and decrease products --or this is called leftward shift in the equilibrium or reverse reaction rate is greater than forward rate --equilibrium constant does not change during this shift --Q less than K indicate ratio of product concentration to reactant concentration is less than ratio at equilibrium --meaning reaction shift to increase product and lessen reactants --in other words, it moves toward the right and forward reaction rate is greater --while K is fixed at a certain temperature, Q gives you a snapshot of the reaction change at a point in time such as its reaction shift movement

Bonding and Reactions of Biological Molecules: Fatty Acids and Triglycerides

--fatty acids are long even numbered carbon chains with a carboxylic acid group at one end (H2C-O-C=O-CH2-etc) --remember that fatty acids are amphipathic meaning it contains hydrophobic and hydrophilic end --since hydrophobic carbon chain predominates, fatty acids are nonpolar --fatty acid pK is around 4.5 which allows the molecule to exist in their anion (negative charge state) in the cellular environment --a type of fatty acid is triglyceride which consists of three fatty acid chain and one glycerol molecule --to form triglyceride, hydroxyl group on glycerol act as a nucleophile and attacks the carbonyl carbon of a carboxylic acid group on the fatty acid which creates an ester bond (oxygen lose a hydrogen to connect with a methyl or CH3 at the end) --the formation of lipids is called lipogenesis --reverse process is the lipid breakdown which is called lipolysis --when lipolysis occurs, it catalyze in a process called saponification which makes soap (fatty acid, salts and glycerol) --carbonyl carbon of a fatty acid is the alpha carbon --recall saturated fatty acids has no double bonds while unsaturated has double bonds --saturated fatty acids are straight and solidify better while unsaturated has kinks (making it have lower melting point) --trans fat are synthesized in a lab for profit and, because of its unique shape, it is not easily broken down --the human body doesn't have the enzymes to break them down for excretion

Energy and Reactions: Gibbs

--for the sake of convenience, scientists prefer to focus on the system as often as possible when analyzing --Gibbs free energy or thermodynamic property is written as G=H-T*S with S stands for S.system and H stands for H.system (measure of heat flow into and out of the system) --recall that heat is the measure of random kinetic energy which increases disorder of the environment --since second law of thermodynamics states that all processes must move in the direction of increasing entropy of the universe, a reaction with positive entropy of the universe (S.universe) is said to be spontaneous --so when delta G is positive, it allows entropy of the universe to be spontaneous since G=-T*S and to get a negative G, entropy needs to be positive --Gibbs energy is useful is quantifying contracted muscles, transmitting nerves and batteries since it only uses non-PV work and free from PV work is what makes it called Gibbs "free energy." --on the MCAT, when you see terms endergonic and exergonic, it means positive delta G (non-spontaneous) and negative delta G (spontaneous). --under certain conditions, DeltaS.system=(-Delta.H.system)/T --Delta G equal to zero indicate equilibrium Key of Enthalpy vs. Entropy on Gibbs Free Energy [G=H-T*S]: 1. Neg enthalpy & Pos entropy create negative G which is spontaneous 2. Neg enthalpy & Neg entropy create either negative or positive G which is spontaneous at low temperature and nonspontaneous at high temperature 3. Pos enthalpy & Pos entropy create negative or positive G which is nonsponatenous at low temperature and spontaneous at high temperature 4. Pos enthalpy & Neg entropy create positive G which is never spontaneous. remember that negative Gibbs free energy is the amount of non-PV work used for reversible process

Bonding and Reactions of Biological Molecules: Carbohydrates

--formation of carbohydrates, amino acids, nucleotides and lipids in a chain through nucleophilic carbonyl reaction are due to the bonds between macromolecules through dehydration or condensation --it is when OH leaves one reactant and H leaves the other to produce a water as a byproduct --it is hydrolysis that water is added to break bonds between biological molecules --hydrolysis is seen in the digestion and enzyme is also required to make and break bonds between macromolecules Common Hydrolysis of Carboxylic Acid Derivatives 1. Acid Chloride R-C=O-Cl + Water 2. Ester R-C=O-OR +water 3. Amide R-C=O-NHR + water 4. Anhydride R-C=O-O-C=O-R + water **all make carboxylic acid R-C=O-OH with its unique produce such as HCl, ROH, RNH2 or RCOOH Carbohydrates: --carbon chains with an alcohol on each carbon except for one which has either an aldehyde or ketone (C6H12O6) --it forms into a ring since an alcohol group on carbon 5 (furthest away from the carbonyl) acts as a nucleophile addition and attacks the carbonyl --in aqueous solution, carbohydrates exist predominantly in ring form --in order for monosaccharides to form polysaccharides, the monosaccharide undergo intermolecular nucleophile substation reaction with other monosaccharides --two monosaccharides together makes acetal --carbohydrates containing aldehydes are called aldoses while carbohydrates containing ketones are called ketoses --When the hydroxyl group CH2-OH is faced toward the right, this represents the D configuration or D-glucose or dextrose --the human body can only produce D-fructose or D-glucose, think D as delicious --if the group is faced to the left, it is classified as L --carbohydrates with the same structure but different configuration around a single chiral center is known as epimers or stereoisomers --chiral carbon is created at carbon 1 of the right (all the way to the right) and on the Fischer projection it is on the carbon of the very top or H-C=O --carbon 1 is the one attached to two oxygens and is the carbonyl carbon which is also called anomeric carbon --if the alcohol group of carbon 1 is pointing downward, it is an alpha anomer. but if it is facing upwards on the ring structure, it is a beta anomer --a ring structure with 5 members including oxygen is called furanose while a 6 member ring is a pyranose --for glucose rings, it is a glucopyranose --when you see a glycose with a name with -oside like methyl glucopyranoside, this indicates that the sugar is attacked by an alcohol to create an acetal (https://en.wikipedia.org/wiki/Acetal) --as you can see in the ring structure, the methoxy group CH2OH and hoydroxyl group CH (connected to the COCH3) are facing the same side which it is why it is an alpha glucopyranoside --disaccharides and polysaccharides are glyosidic linkages which can be broken slowly through hydrolysis --to speed up hydrolysis, it required enzymes --glyosidic linkages are named by the numbers of carbons involved in the bond --there are three common bonding arrangements between sugars; 1,4' link, a 1,6' link, and a 1.1' link Check out side--> https://chem.libretexts.org/Bookshelves/Organic_Chemistry/Map%3A_Organic_Chemistry_(Wade)/24%3A_Carbohydrates/24.07%3A_Disaccharides_and_Glycosidic_Bonds --when dehydration reaction occurs, the water is removed from the molecules to cause bonding between glycosides. another name for this reaction is acetal formation --humans lack enzyme to digest and break down beta 1,4' glucosadic linkage in cellulose --people with the condition of lactose and intolerance lack the enzymes to break beta 1,4' galactosidic linkage in lactose Common Disaccharides and polysaccharides (mostly glycosidic linkage): 1. Sucrose --> 1,1' or 1,2' linkage between alpha glucose and beta fructose 2. Maltose --> alpha 1,4' linkage between two glucose molecules 3. Lactose (galactosidic linkage) --> beta 1,4' linkage between galactose and glucose 4. Cellulose --> beta 1,4' linkage between pairs of chain of glucose molecules 5. Amylase (starch) --> alpha 1,4' linkage of pairs of chain of glucose molecules 6. Amylopectin and glycogen --> alpha 1,4' linkage between a branched chain of glucose molecules with alpha 1,6' linkages forming the branches Link: https://slideplayer.com/slide/5909469/ **glycosidic linkage is a covalent bond joining sugar or carbohydrate molecules to another group that may or may not be another sugar** **for the mcat, know the structure of glucose well in both straight chain and ring form. Link: https://slideplayer.com/slide/8449984/**

Nitrogen as a Nucleophile: Amines

--functional groups within a molecule can be classified as electron withdrawing or electron donating --electron withdrawing groups or EWG are strongly electronegative and can pull electron density from the rest of the molecule ex. EWG can draw electrons away from the acidic proton (H+) which makes alcohols or the molecule more acidic and increase its partial positive charge --at the same time, the EWG stabilize the negative charge portion --unlike EWG, electron donating group (EDG) gives electrons which stabilize positive charge and acid portions making it more basic ex. alkyl groups donate electron which increase basicity and decrease acidity of alcohols Nitrogen: --behaves similar to oxygen --it is a really good nucleophile and the worse leaving group than oxygen --nitrogen shares its electron more readily with carbon in a bond than oxygen because carbon and nitrogen are closer electronegatively --this makes C-N bonds strong, less reactive and less polar than C-O bonds --molecules with nitrogen are known as amines Nitrogen Can Form 3 or 4 Bonds: --ammonia is NH3 --primary amine is NH2-R --Secondary amine is NH-R2 and so fourth (tertiary and quaternary) --special rule is that four bond nitrogen (NR4-quaternary) has a positive charge --uncharged nitrogen like ammonia, primary, secondary and tertiary all have lone pair electrons on the nitrogen. Remember to draw lone pairs when these appears on the MCAT Remember (when amine appears): --nitrogen acts as a nucleophile which means the lone pair electrons attack a positive charge --nitrogen can take on a fourth bond to become positively charged --nitrogen typically reacts with aldehydes and ketones in nucleophilic addition reactions --but for nucleophilic substitution reactions, nitrogen react with carboxylic acids --since ammonia and amine act as a base, it can donate their lone pair of electrons --if you remove the amine, the basicity decreases Link To Recall Nucleophilic Addition vs. Substitution: https://www.youtube.com/watch?v=cvZhc54pPzA

Heat

--heat and work are the two ways energy is transferred between systems --heat (q) is spontaneous and moves from warmer to cooler body --heat transfer happens when there are random collisions between molecules of two systems --the warmer body becomes cooler due to a net loss of energy and the cooler body becomes warmer due to a net gain of energy --the two bodies eventually reaches equilibrium which is when they have the same temperature and kinetic energy --while the collisions continue to occur, the net transfer of energy between two bodies stops --when two bodies at different temperature are placed in thermal contact, the temperatures of the two become equal and try to reach between two original temperatures --Zeroth Law of thermodynamics states that two systems in thermal equilibrium with a third system are in thermal equilibrium with each other --the zeroth law was made after the first, second, and third law were established and discovered that these laws were dependent on the existence of temperature Energy transfer through Heat: 1. Conduction--> thermal energy transfer with molecular collisions from one system of higher energy molecules to lower energy molecules. --requires direct physical contact. --object's ability to conduct heat is called thermal conductivity k or warms up something else 2. Convection--> thermal energy transfer with fluid like liquid or gas movements --depends on pressure or density that drives warm fluid in the direct of cooler fluid 3. Radiation--> thermal energy transfer with electromagnetic waves --ex. is a metal heated which initially glows red but eventually turn into blue-white which is when hot metal radiates visible electromagnetic waves --radiation is the only type of heat transfer that can occur through a vacuum Solving for Heat in Power: --all objects with a temperature above 0 K radiates heat and the rate of releasing electromagnetic waves depends on temperature and surface area --solving for electromagnetic waves rate (power P) can be done by P=σ*e*A*T^4 --where σ is the Stefan-Bolzman constant (5.67x10^-8 W m^-2 K^-4) --A is the surface area while T is the temperature in Kelvin --another equation is P=σ*e*A(T.e^4-T.o^4) which is used when there is a heat transfer --T.e stands for temperature of the environment while T.o is the temperature of the object --in fact, Newton's law of cooling states the body's rate of cooling is proportional to the temperature difference between the body and its environment --when heat is transferred to an object's surface, only a fraction is absorbed and the rest is reflected --but the amount of what is absorbed depends on the surface level of emissivity (ex. higher emissivity as a 1 indicate higher amount of radiation energy absorbed, so almost 100% which is called blackbody because it appears totally black) --this also means dark colors tend to radiate and absorb better than light colors which tend to reflect

Effects of Solvent on Rate

--in general, liquid molecules have 100x more collisions per second than gas molecules because liquid molecules are more closer to each other --but, liquid collisions do not lead to a reaction since the collisions are with solvent molecules and not with reactant molecules --solvents are electrically insulate reactants so it reduces electrostatic forces between them --it also helps stabilize reaction intermediates --when a reactant is dissolved in a solvent, it becomes solvated, meaning more spread out and become surrounded by solvent molecules --imagine a cage full of solvent molecules, if there is not another reactant in the solvent cage, the molecules cannot react unit it escapes --between solvent molecules, they rattle around at tremendous rate to make several collisions --therefore, stirring and shaking greatly increase number of collisions and thereby reaction rate --what increase kinetic or movement is temperature

Photoelectric Effect

--in summary, photon released when electrons falls to lower energy shell --photons absorbed when electrons bump up to excited state --photoelectric effect proves the existence of one to one; photon to electron collision ex. one to one collision demonstrate light is made up of particles --in fact, Einstein insisted that light shining on a metal causes emission of electrons (photoelectrons) --intensity of light shining on a metal increases as the number of photon increases --keep in mind kinetic energy of emitted electron (energy of wave) is proportional to intensity --but Einstein was sort of wrong, actually intensity increase as frequency of each photon increase resulting higher kinetic energy of electrons --low frequency even less than quantum energy means no electrons emitted regardless of the number of photons --in other words, insufficient energy of photon hinders electrons from emitting --this demonstrates how electrons must be spit out by one to one photon-electron collisions rather than combined energies of photons --the minimum amount of energy needed to eject electron is called work function (Φ) --you can use work function to solve for kinetic energy of ejected electron KE=(h*f)-Φ --h*f is the energy put by a photon while Φ is the energy required to eject electron from the atom --energy left over is the electron's kinetic energy

Internal Energy

--internal energy is the sum of energy of molecules measured on a microscopic scale --the collective energy could be vibrational energy, rotational energy, translational energy, electronic energy, intermolecular potential energy, and rest mass energy. --internal energy does not include macroscopic mechanical energies such as kinetic energy of the entire system --it is reserved to different forms of energy within a system Vibrational energy: provides insignificant contribution to internal energy for light diatomic molecules at temp below a few hundred Kelvin --monoatomic gas has no vibrational energy since there is a lack of covalent bonds around which to vibrate Rotational energy: is the spatial orientation of a molecule around its center of mass changes while the center of mass remain fixed. --monoatomic gas has no rotational energy as well Translational energy: movement of the center of mass of a molecule --monoatomic gas has translational energy which contribute to kinetic energy Electronic energy: created by the attractions between electrons and their nuclei --potential electrical energy changes when there is the greatest change in internal energy --electronic energy basically remains constant when there isn't a chemical reaction Intermolecular potential energy: created by intermolecular forces between molecular dipoles --it is only when the increases significantly that the intermolecular potential energy makes a large contribution to internal energy (either in liquids and solids) Rest mass energy: it is the Einstein's famous equation E=m*c^2 --sum of this energy for a large group of molecules is the internal energy. --it can also be thought as the sum of kinetic energy and potential energy contained within a system --recall that vibrational, rotational, and translational energy are types of kinetic energy --electronic, intermolecular and rest mass energy are types of potential energy --remember internal energy is a type of state function (change in physical condition) and internal energy of an ideal gas is only dependent on temperature so not volume. --ideal gas is like a bunch of tiny, volume-less marbles bouncing off each other --when there is a change in internal energy of an ideal gas, there is a temperature change --the MCAT may refer internal energy as heat energy, thermal energy or even heat --heat or thermal energy (affecting temperature) are really vibrational, rotational, and translational parts of internal energy --don't confuse the idea of heat as transfer of energy

Entropy

--it is common to know that entropy is nature's tendency toward disorder --entropy (s) is also nature's tendency to create the most probable arrangement that can occur within a system ex. if four beans where to jump between two jars, it is 6 times more likely to take two beans in each container than having four beans in one container --entropy is also described at nature's effort to spread energy evenly between systems --so when entropy of system decrease, the entropy of the surrounding increases since it moves from system to surrounding and so forth ex. a warm system will lose energy to its surrounding when it is placed in a cool room --essentially energy is not gained or lost, it is spread out --this also means entropy is involved since it drives reactions in a given direction. it is true since second law tells you that entropy of the universe is the driving force that dictates whether or not a reaction will proceed --in order to process, a reaction must increase entropy of the universe and not necessarily the system --second law of thermodynamics state entropy of an isolated system will never decrease unless there is an outside intervention but it is less likely --equation to understand is that entropy of the system plus the entropy of the surrounding makes up or equal to the total entropy change of the universe which can be equal to or greater than zero --another way entropy increases is by increasing the amount of substance or by increase with number, size, volume, and temperature --on the MCAT when it says a reaction increases the number of gaseous molecules, just know entropy is positive for the system but not necessarily for the surroundings or universe --at absolute zero entropy, it means the element or compound is in its solid form and internal equilibrium since it has very little motion --entropy units are J/K or heat per kelvin or it can be defined as S=q.rev (heat)/temp --it is defined as a reversible process and heat transfer between two states --think of entropy as trying to spread energy evenly throughout the universe --think of when a system is isolated, the forward reaction does not affect the surroundings and cannot change the entropy of the surroundings

The Targets: Electrophiles

--it is molecules with a tendency to accept electrons to form new chemical bonds --it essentially holds a positive charge which wants to receive electrons from the nucleophiles (nucleophiles remember attacks to give electrons to partially charged atoms) --electrophiles are targets of nucleophiles --most common electrophiles on the MCAT are carbonyls, aldehydes, ketones and carboxylic acids --carbonyls are carbons double bonded to an oxygen and all the common electrophiles have this feature --when you see a carbonyl, think about.. 1. Planar Stereochemistry; very receptive to attack due to its open space above and below making oxygen easily protonated and carbon prone to be attacked 2. Polarity since partial neg on oxygen while partial pos on the carbon --while acyl chloride (having a carbonyl) is more reactive because electron density is withdrawn or pulled away from the carbon, amide (having carbonyl) is more stable because of donating electrons density to carbon --carbonyls with leaving groups are attacked by nucleophiles and undergo a substitution reaction meaning the leaving group is replaced --carbonyls without a leaving group undergo addition reactions which means carbon is bonded only to hydrogens or other carbons --essentially, the nucleophile adds to the molecule to allow C-H and C-C bonds intact --like acid-base reactions, the acyl chlorides and esters undergo nucleophilic substitution since chloride ion leaves and the -OR group in the latter --another type of nucleophile substitution reaction is amides since nitrogen stays (more positive) while oxygen from the bonded carbon leaves --Aldehyde and ketones do not have a good leaving group and a good open space above and below --so these molecules are likely to get attacked from either side and undergo addition reaction which produces racemic mixture (R and S equally) or possibly stereoselective (either R or S) --stereoselective may hinder further attack by nucleophiles from either side of the carbonyl --unlike stereoselective, stereospecific have very different or specific stereoisomer which are not preferred over the other Link of helpful rules: https://www.organicchemistrytutor.com/topic/stereospecific-vs-stereoselective-reactions/ **overall electron withdrawing groups allow carbonyls to be more positive while electron donating groups make carbonyls more negative and less reactive**

Representation of Organic Molecules - Lewis Structures and Formal Charge

--keep in mind that negative regions with high electron density attack positive regions with low electron density --lower energy is less reactive and more stable --higher energy is less stable and more reactive --when seeing an organic chemistry reaction, look for what changed from reactants to products ex. did bonds form or broken, did functional groups appear or disappear Lewis Structure or Lewis Electron Dot Formula --> provides details about each atom's valence electrons and there are three rules to consider when drawing the structure... 1. find the total number of valence electrons for every atom in the molecule 2. use one pair of electrons to form a single bond between each pair of atoms 3. arrange the remaining electrons in lone pairs and double or triple bonds to satisfy the duet rule for hydrogen (C-H) and octet rule for other atoms (C-:O:-H) --octet rule may not exist for certain atoms from the third period or higher on the periodic table which will hold more than 8 valence electrons --Sulfur is most commonly seen with an expanded octet --other valences (number of bonds) that are common for atoms in organic chemistry are carbon and silicon-tetravalent (4 valence), nitrogen-trivalent, oxygen or sulfur-divalent and hydrogens and halogens(like fluorine or chlorine) are monovalent --phosphorus has 3 valence and one double bond Formal Charge: lewis structure can determine this of an atom by the number of valence electrons of an atom excluding the number of bonds and numbers of nonbonds ex. carbon as a form of a cyanide ion Carbon-Nitrogen or CN can have 4 bonds which can be written as a carbon with triple bond (3 electrons) and a pair of electrons (2 electrons) equaling a total of 5 electrons. since a neutral carbon has four valence electrons or four bonds, the formal charge on the carbon in a cyanide ion is -1 or [CN]^-1 --in other words, formal charge=(#valence electrons)-(#bonds)-(#nonbonding electrons)

Phases & Behavior of Gases

--keep in mind, intramolecular bonds are interactions between one part of a molecule and another part of the same molecule --intramolecular bonds are very strong as a case in covalent bonds --intermolecular bonds act between two or more different molecules --these forces are usually attractive to hold molecules of a substance together --ex. are solids and liquids have strong intermolecular forces meaning the molecules are held closer --when a solid transition to a liquid and then to a gas, translational motion, particle speed, and space between molecules increase --but intermolecular forces decreases --while intramolecular bonds remain the same in all phases, phase change is the forming and breaking of intermolecular bonds --while bonds store potential energy, temperature is equal to kinetic energy --higher degree of compression favors solids while a lower degree of compression favors gases --liquid is intermediate between these two extremes --degree of compression is impacted by external pressure --if external pressure is low, molecules will expand and behave more like gases --remember molecules with higher kinetic energy and this higher temp are more likely to break free of intermolecular bonds and exist in fluid phases of liquid and gases --the gas molecules end up moving faster and behave more ideal or typical gas Behavior of Gases: --typical real gas is a loose collection of weakly attracted atoms or molecules moving rapidly in random directions --while only 0.1% of the total volume occupied by gas, about 70% of the total volume is liquid --standard temperature and pressure (STP) is known as 0C and 1 atm --at this stage, gas molecules are fairly spread out --gas molecules are far apart so the attractive forces are so small --gas molecules move at tremendous speed --mean free path is the distance traveled by a gas molecule between collisions --some kinds of molecules have a mean free path that is short distance but completed at high speed which makes some chemical reactions occur instantaneously --mixture of gas compounds will be homogenous because they are so far apart that they exert repulsive force or small/unaccounted attraction --although water and gasoline do not mix well together in liquid form, in gas phase they form a homogenous mixture --due to homogenous, gas molecules cannot separate based on polarity differences, they can based on density --under low temperature, gravity causes more dense gases to settle beneath less dense gases ex. cold CO2 gas from fire extinguisher is heavier than air

Chirality and Configuration

--many pharmaceutical drugs, nutrients or molecules are chiral meaning mirror images acting differently inside the body --for the MCAT, chirality is mainly concerned with carbon --carbon is chiral when it is bonded to four different substituents --Absolute Configuration is the only way to describe the physical orientation of atoms about a chiral-carbon center --two possible configurations that are mirror images; R (Right) or S (left) --first, the highest priority is given to the largest atomic weight --exception of first priority is dark wedge goes first before the larger weight --second highest is double or triple bonds --third priority is dashed wedge or lowest weight --hydrogen is always the lowest priority --once you label the priorities (priority 1, 2, 3 etc), draw an arrow of the direction it moves (from 1 to 3) and the fourth or last priority molecule is facing into the page --the direction can be clockwise (absolute configuration of R) or counterclockwise motion (absolute configuration of S) --trick to remember, arrow moving to the Right is absolute config S since counterclockwise is from 12pm to 9pm and vice versa --mirror image of chiral atom always have an opposite absolute configuration like enantiomers. --while absolute configuration is about R and S notation system, relative configuration uses cis- or trans- --think of absolute configuration as longitude and latitude written out while relative configuration is the map showing where that certain place is located --relative configuration cis is when functional groups have both dark wedges or both dashed wedges --relative configuration trans is when functional groups have opposite dark and dash wedges --brief tutorial: https://www.youtube.com/watch?v=kFD6hzLseVs

Oxygen Containing Reactions

--most relevant to biological processes are reactions of carbonyls which can be found in sugars, proteins, fats, and nucleic acids --carbonyls are usually attacked by a nucleophile at the carbonyl carbon --but it can sometimes become nucleophiles at the alpha carbon which is adjacent to the carbonyl carbon --remember alcohols (O), amines (N) and hydrides (H+) are often the nucleophiles that attack carbonyl carbon --C=O double bond is often the site of reactivity in biological molecules

Radioactive Decay

--nuclear decay involves the degradation of particles within the nucleus of an atom --recall that atomic nuclei is held together by strong nuclear force --neutrons space out the protons which stabilize the nucleus --radioactive decay involves spontaneous degradation of atoms as a whole --only hydrogen is the only atom that is not subject to spontaneous decay --what defines atoms radioactive is how high their decay rate --half life is the length of time or rate for 1/2 of a given amount of substance to decay --carbon dating uses the principles of radioactive decay to determine how old organic matter is --another use is radioactive isotopes for biomedical imaging --equation to remember A.t=A.o*e^(-kt) or ln(A.t/A.o)=-kt which can help figure out the amount of atoms remained after decay --A.t is the amount of time, A.o is the original amount, k is the rate constant and e is a constant (making radioactive decay is a type of exponential decay) --logarithm of amount of atoms or amount of radioactive nuclei (y-axis) as a function of time (x-axis) produce a semi-log plot --four possible variables for half life problems are initial amount of substance, final amount of substance, the length of half life and number of half-lives (often given as a time period) --number of half-lives is simply divided by the length of a half life --MCAT questions will provide three of these variables in some form and ask you to find the fourth Ex. how long it takes for 500 grams of a substances with a half life of 2 years to decay to 62 grams... 500/2 is 250, 250/2 is 125 and 125/2 makes 62.5. so 3 half lives or 6 years

Reaction Order

--order of each reactant indicates the particular influence of that reactant ex. reactant with a zero order indicate reaction rate does not depend on that reactant --this occurs when concentration of the substrate (or reactant) far outweighs the concentration of the enzyme --recall when enzyme retrieves or uses substrates to produce reactions and increase its rate --but when there are too much reactants, it starts to have no effect on the reaction rate --for first order reaction, reaction rate is directly proportional to the concentration of a single reactant ex. is radioactive decay A-->products --second and third order reactions come in two types --first type is reaction rate is equal to a single reactant's concentration raised to the second or third power ex. 2A-->products 3A-->products or rate=k.f*[A]^2 rate=k.f*[A]^3 --second type is reaction rate is equal to the product that is derived from the concentrations of multiple reactants ex. A+B-->products A+B+C-->products or rate=k*[A][B] second order rate=k*[A][B]^3 third order rate=k*[A][B][C] third order --order of the overall reaction provides more general information about the relationship between reactant concentrations and reaction rate --or order of the reaction is the sum of the exponents in the rate law --sometimes a reactant raised to the power of 1 or first order is written without an exponent --if a reactant does not appear in the rate law, then that reactant has an exponent of zero --keep in mind, mcat way give you reaction order graphs; with reactants on the y-axis and time on the x-axis --slopes for zero and first order are straight, linear and moving from top of the y-axis line descending down to the right side of the x-axis so k.f is negative --slopes for second and third order starts below middle of the y-axis line and head upward which does not touch x-axis line so k.f is positive --regardless if slope of k.f is positive or negative, the value of rate constant does not change since it is constant!

Atoms

--tiny particles that up a mass or matter --each atom is composed of a nucleus surrounded by one or more electron --the radius of a nucleus is based on 10^-4 angstroms (A) and one angstrom is 10^-10 meters. --the nucleus consists of protons and neutrons which both are about the same size and mass --protons and neutrons hold together to form the nucleus by strong nuclear force --the stability of the nucleus depends on its binding energy which is the energy required to break the nucleus into individual protons and neutrons --electrons are located approximately 1 to 3 angstroms --mass of an electron is more than 1800 times smaller than mass of a nucleon --matter is like a football stadium which has a nucleus the size of a marble making matter mostly empty space --also, electrons are much smaller than nucleons and atomic mass is the total number of protons and neutrons whose mass is the same (about 1 amu) --a charge of one electron is 1.6x10^-19 coulombs

How to Use Periodic Table

--periodic table lists the elements from left to right in the order of their atomic numbers --each horizontal row is called period which is read from left to right (18-big to 1-small) --vertical columns are called groups or families which is read from bottom to top (VIIIA-big to IA-small) --Memorize; alkali metal in group 1 or IA, alkaline earth metal in group 2 or IIA, oxygen group 16 or VIA, halogen group 17 or VIIA and noble gases in group 18 or VIIIA. --Group A are representative elements or main-group elements --Group B are called transition metals --elements in the same family share similar chemical and physical properties --the periodic table on the MCAT does not have group numbers which means the periodic table is NOT organized by numbering groups 1-18 from left to right --instead, groups are separated into sections A and B and then number them with Roman numerals. --Elements are divided into 3 sections; 1 is nonmetals on the right, 2 is metals in the middle and on the left, and then 3 is metalloids that separate metals from non metals (middle-ish) Metals: --large atoms that tend to lose electrons because of its "sea of electrons" to form positive ions (cations) and positive oxidation states --also to help form ionic bonds --its easy movement of electrons within, easily stretched (ductility), easily hammered into thin strips (malleability), thermal and electrical conductivity are what gives them their metallic character --essentially metal atoms easily slide past each other so it can be hammered into thin sheets and drawn into wires --electrons can move easily from one metal atom to the next, transferring energy or charge in the form of heat or electricity --transitional metals form ions by losing electrons from the highest s-subshell and then from the d-subshell --essentially atoms that lose electrons will start from the highest energy shell Nonmetals: --have diverse appearances and chemical behaviors --they have lower melting points than metals and tend to form anions --typically anions react with metal cations to form ionic compounds --metalloids have both metallic and non-metallic characteristics --representative elements like to form noble gas (type of group like halogen group) electron configurations when they make ions in order to seek symmetry --ex. group 1 atom form 1+ cations and group 17 atoms form 1- atoms --unlike representative elements, transition metals try to even out their d-orbitals so that each orbital has the same number of electrons

Phase Diagrams (Heat Curve Graph)

--phase diagram represent the phases of a substance at different pressure and temperature --the lines on the graph of each section represent where corresponding phases are in equilibrium with each other --each section represent different phases --when water and steam are in equilibrium, water molecules escape from the liquid phase at the same rate as when water molecules return to liquid phase --critical temperature is when a substance cannot be liquefied regardless of pressure applied --the pressure required to overcome critical temperature is called critical pressure --critical point is the combined critical temp and critical pressure --supercritical fluid is when a substance has both gas and liquid characteristics meaning it is beyond critical point --when there is low pressure, molecules will spread far apart --when internal pressure is high, molecules forced together and solid phase is favored --to get internal molecules to move fast that makes it overcome the intermolecular forces or bonds break free, add high temp (opposite to low pressure) --on the phase diagram, pressure in atm is on the y-axis while temperature is on the x-axis --solid region shown toward the very left, liquid top middle and gas bottom to the right --remember, during equilibrium, bonds break or form while temperature does not change --but during the phase change process, energy increases molecular movement which increase temp --phase diagram is different for certain molecules --ex. water's critical point (all three phases) is at 1atm while the critical point of carbon dioxide is much higher than 1 atm --at 1 atm, carbon dioxide undergo sublimation (solid to gas) --besides seeing how regions from solid move to gas, you should pay attention to the lines dividing every phase change section --ex. at 1 atm, a straight line is drawn across the diagram. from solid to liquid, the dividing line (or curve) between the two phases is shown to be decreasing making a negative slope --link of diagraph: https://theory.labster.com/phase_diagram/

Acids and Bases

--polyprotic acids are capable of donating more than one H ion --Lewis defines an acid as any substance that accepts a pair of electrons and a base are substances that donates a pair of electrons --lewis acids do not have an incomplete octet of electrons around the central atom --the smaller the cation and higher the charge, the more electrophilic in nature and stronger the acid strength ex. Fe3+ --an acid reacts in water to produce H --base reacts in water to produce OH --the H and OH often comes from H2O rather than acid or base --when pH is lower than pKa, it means there is more H ions or the environment is protic --protic indicate the species in the environment will act less acidic --when pH is greater than pKa, the environment has fewer H ions and the species will act more acidic --Arrhenius acid is a substance that produces hydrogen ions in water or aqueous solution --while an Arrhenius base is a substance that produces hydroxide ions (OH) in water --Bronsted-Lowry is any acidic substance that donates proton H and a base as any substance that accepts a proton --basically Bronsted defines acid to donate while for Lewis defines acid to accept --in fact, aqueous solution containing greater concentration of H than OH is acidic and vice versa for basic --neutral aqueous solution has equal amounts of H and OH --strong acid is considered when an acid cannot hold on to its hydrogen or can easily lose it --weak acid is when an acid has a strong hold on its hydrogen

Determining the Rate Law by Experiment

--rate law on the mcat is relatively straight forward since it will be kept simple --recall hypothetical reaction 2A+B+C-->2D --in this case assume there isn't a reverse reaction ex. trial 1 to trial 2 initial concentration of A goes from 0.1 to 0.2 meaning it doubled. but initial concentration of B and C remain the same --rate of reaction is proportional to concentration of reactant A meaning reaction rate (initial rate of D) doubles --so [A] receives an exponent of 1 ex. lets say trial 2 and trial 3 are compared so the initial concentration of A and C remains the same. but initial concentration of B doubles (2x) --rate of reaction is proportional to the square of concentration B meaning reaction rate (initial rate of D) quadrupled --to get to 4 (quadrupled) [B] receives an exponent of 2 in the rate law. ex. when comparing trials 1 and 4, all initial concentrations remain the same besides C. it goes from 0.1 to 0.4 meaning it quadrupled. --since rate of reaction is independent of concentration of C, reaction rate has no change and [C] receives exponent of zero in the rate law --overall, it can be written as rate=k.f*[A]^1*[B]^2*[C]^0 or rate=k.f*[A][B]^2 --when adding all the exponents (1+2+0=3) it shows reaction is third order --rate constant k can be solved once rate law has been derived from experimental data --greater the concentration of a species, more likely it will collide with other reactants, hence rate increases

Determining Reaction Rate

--reaction rate is how quickly concentrations of the reactants or products are changing over the course of the reaction --a type of reaction MCAT will test on is kinetics on gases or dilute solutions at constant temperature --rates typically represented in units of molarity per second (M s^-1 or mole L^-1 s^-1) or change in concentration of reactants and products over time --recall that pressure, temperature and concentrations of substances in a system (disappearance of reactants or appearance of products) can affect rate of reaction --remember stoichiometric equation aA+bB-->cC+dD where lowercase letters are moles or how many molecules involved in reaction collision --this equation is also elementary reaction which occurs in a single step --on the MCAT do not assume a reaction is elementary unless it is stated since it is difficult to distinguish an elementary reaction from a multistep reaction --average reaction rate over time is written as rate=(-1/a)(delta[A]/t) = (-1/b)(delta[B]/t) = (1/c)(delta[C]/t) = (1/d)(delta[D]/t) --the negative sign indicate reactant concentration decreasing --remember the lowercase letters in the denominator are stoichiometric coefficients or moles which provide more information of reactant rate used and product formation ex. 2N2O5-->4NO2+O2 one unit of O2 is produced for every two units of N2O used --keep in mind that reactants are transformed into a new substance instead of a physical reaction --also rate expression shows N2O5 disappears at double rate that O2 appears --an intermediate is a molecular entity that is formed from the reactants and reacts further to give the directly observed products of a chemical reaction. --essentially, catalyst is used at the beginning of the reaction and regenerated at the end. --while an intermediate is produced during the reaction but no longer exists by the end ex. step 1 O3-->O2+O step 2 O3+O-->2O2 --if you cross off oxygen from reactant side in step 2 and oxygen from product side in step 1, oxygen doesn't appear in the overall equation 2O3-->3O2 --most chemical reactions are reversible: as the products are formed, they begin to react to reform the reactants --Rate law explains how initial reaction rates used to derive an expression for reaction rate rate.reaction=k.f([A]^a)([B]^b) --k.f is the rate constant (stays the same but is influenced by pressure, temp and concentration) --to solve for k is moles/second = k (M)^a(M^b) and cancel out moles --while a and b are reaction order --unless you are told equation is elementary reaction, never assume that you can use coefficients of balanced equation in rate law --know the relationship between rate law and elementary reaction (rate of reaction or rate forward in moles/second) --check out this video to understand https://www.khanacademy.org/science/ap-chemistry-beta/x2eef969c74e0d802:kinetics/x2eef969c74e0d802:introduction-to-rate-law/v/rate-law-and-reaction-order --overall order is a+b

Chemical Potential and Redox Reactions

--redox reaction stands for oxidation-reduction reaction --it is the transfer of electrons from one atom to another --atoms that loses electrons is oxidized --atoms that gain electrons is reduced --oxidation state is the charge values that an atom can possibly hold within a molecule --essentially, this helps keep track of the movement of electrons --if atoms had permanent oxidation states, redox reactions could not take place --when the two tables or guidelines below conflict, the first table is given priority ex. lets say you are given NO3^- which is nitrogen. based on the first table, the oxidation state of atom oxygen is -2. so the oxidation state of nitrogen will be +5 because 5-2 is +3 which is the oxidation state of nitrogen according to the second table or guidelines --another example is 2H2 + O2 --> 2H2O --hydrogen is oxidized according to this reaction because, based on the general guidelines, hydrogen loss electrons from 0 to +1 --oxygen has been reduced since it has a oxidation state from 0 to -2 or gained 2 electrons --in any redox reaction, there are both a reducing (reductant) and oxidizing (oxidant) agent, like how it is shown in this example --reducing agents give electrons to another species --reducing agents are what being oxidized in order to give up some of its own electrons --oxidizing agent contains atom that is being reduced or gaining the electrons --these agents are not atoms but compounds such as Ni or NiO2 General Oxidation State Rules (must be known for MCAT): --oxidation state of zero has atoms in elemental form --oxidation state of -1 is fluorine --oxidation state of +1 is hydrogen atom --oxidation state of -2 is oxygen atom Group Oxidation States: --oxidation state of +1 is group 1 elements or alkali metals --oxidation state of +2 is group 2 elements or alkaline earth metals --oxidation state of +3 is group 15 elements or nitrogen family --oxidation state of -2 is group 16 elements or oxygen family --oxidation state of -1 is group 17 element of halogens Redox Titrations --> it is used to find molarity of a reducing agent --the way to do that is to titrate sample with a strong oxidizing agent --then measure the resulting voltage change --in order to have a voltage, the solution must be different from another solution --the other solution is known as standard solution --the solution with the reducing agent has a potential difference or voltage --as you add strong oxidizing agent to the solution, the voltage increase but eventually quite suddenly --on a graph, there is a half equivalence point near the middle of the gradual increase or point where the voltage suddenly shoots up --voltage is monitored using a voltmeter --equivalence point occurs when all the moles of reducing agent in the solution have been completely oxidized ex. you have 100mL of a solution with an unknown concentration of Sn2+ ions --to determine the concentration, titrate with a 5 mM reagent of the strong oxidizing agent Ce4+ which is given as 2mL. --Sn2+ gives up 2 electrons while Ce4+ (oxidizing agent) is what being reduced gains one electron --this is because Ce4+ reduced to Ce3+ while Sn2+ oxidized to Sn4+ --to find Ce4+, apply 2mL x 5mmol x 1L/1000mL = 0.01 mmoles of Ce4+ --to find concentration of Sn2+, think of how 2 atoms of Ce4+ oxidize only 1 atom of Sn2+ --so then 0.01 mmoles of Ce4+ is required to oxidize 0.005 mmoles of Sn2+ --therefore (0.005mM of Sn2+)/(100mL solution) x (1000mL/L) = 0.05mM Sn2+

Kinetic Molecular Theory Part 2

--simple mercury barometer is an instrument to help measure atmospheric pressure --the instrument has a tube of mercury that inverted and placed in an uncovered mercury bath --the bath is open to the atmosphere --mercury will fall down into the bath and the remainder will be suspended above in the tube --the amount of mercury left in the tube represent the atmospheric pressure pushing down on the mercury bath --equation to use with this instrument is P.atm=ρ*g*h where ρ or rho is the density of mercury in kg/m^3 --g is the gravitational constant (9.8 m/s^2) and h is the height of the mercury above the bath in meters --keep in mind that 1 atm is equal to 760 torr or 760 mmHg --remember that volume of gas is directly proportional to temperature --this is known as Charles' Law: V/T=constant --volume of the container is also proportional to number of molecules while temperature and pressure is constant --this is known as Avogadro's law or V/n=constant --so two things to consider right away when gas expands, either temperature increase because it is proportional to volume or pressure decrease. so more information is required --also, according to the equation for work (w=-P*V) with either change in pressure or volume of gas, there is an impact of work --hence, work can be used to determine internal energy E=q+w which means the container will have molecules inducing work and heat transfer --insulated systems have a physical process change without the transfer of heat between gas and its surrounding. this is known as adiabatic where q=0 in E=q+w and work is negative since energy is negative --this happens when when the volume expanse, the internal energy energy of the gas decreases making work negative --since they are related, when internal energy decrease the temperature also decrease and according to PV=nRT, pressure must decrease --isothermal is when physical process occurs without any change in internal energy --to understand PV=nRT, pressure decrease due to loss of kinetic energy, decrease in temperature and work, but increase in the container volume --when the gas is not insulated from its surrounding, it will have the same temp as the outside --heat then can be exchanged between gas and the environment --to stay within gas law, when the surrounding is heated, the volume and temperature increase --work is done on expansion which allow more transfer of heat --gas is unaware of the other gases and kinetic energy is conserved when molecules collide Overall Process Types: 1. Adiabatic Process --> no heat transfer meaning q=0 and E=W 2. Isothermal Process --> no change in internal energy meaning E=0 and q+w=0 3. Isovolumetric Process --> no change in volume and no work meaning w=0 and E=q Overall Ideal Gas Law Special Cases: Charles' Law --> volume of a gas is equal to temperature at constant pressure Boyle's Law --> volume of a gas is inversely proportional to pressure at constant temperature Avogadro's Law --> volume of gas is equal to the number of moles at constant temp and pressure. **standard temperature and pressure (STP) refers to conditions of 1 atm pressure and temperature of 273K or 0C (~298K or 25C)** **one mole of an ideal gas will occupy the standard molar volume of 22.4 liters** **on the MCAT, assume a gas is behaving ideally (ideal gas law or gas law) unless otherwise indicated**

Solution Formation

--solution is a physical reaction so the identities of the compounds do not change --when condensation is occurring, there isn't high pressure causing the formation of most solution --so enthalpy (H) change will equal to internal or overall energy change of the reaction or H=U. this is called heat of solution --you can calculate heat of solution (H.sol) by H.sol=delta.H1 + delta.H2 + delta.H3 etc --remember, lower energy in the system usually indicate higher stability --on the MCAT, assume that dissolution of one condensed phase (liquid or solid) into another increases entropy of the system (or Delta.S) --recall the formula G=H-T*S --entropy is positive but enthalpy can be either positive or negative depending on the type of bonds being made --when enthalpy is negative, deltaG is negative making it a spontaneous reaction --when enthalpy is positive and entropy is also positive, deltaG can be either positive or negative depending on temperature --entropy favors spontaneous solution formation for condense phases (liquid or solid dissolve in liquid) --oppositely, entropy decrease or negative when gasses dissolve in liquids Three Steps Involved: 1. breaking intermolecular bonds between solute molecules (delta.H1 is positive since weaker intermolecular bonds are formed) 2. breaking intermolecular bonds between solvent molecules (delta.H2 is positive since heat or energy is added) 3. formation of bonds between solvent and solute molecules (delta.H3 is negative since it is forming stronger intermolecular bonds and releasing heat) **first two steps in dissolution requires breaking of bond, meaning energy is required so endothermic. the third step is exothermic**

Free Energy and Spontaneity

--spontaneity can be predicted using the relationship between equilibrium constant K and standard state free energy of a reaction ΔG⁰. --ΔG⁰ is different because it is the change in Gibbs energy (delta G) under specific case of standard state condition (1 bar with all species starting at 1 molar concentration and usually at 25C) --Delta G is Gibbs energy that is far less specific than ΔG⁰ meaning energy change for any given reaction under any condition --overall ΔG⁰ is a specific value of delta G calculated when all species have starting concentrations of one molar --standard conditions don't indicate a particular temp and it can have any temperature --but standard conditions typically assumed to be 298K --note that ln(1)=0 Types of Reactions According to Conditions: 1. reactions that do not occur under standard state conditions --> Delta.G=ΔG⁰+RTlin(Q) or rewritten as base 10 logarithm Delta.G=ΔG⁰+2.3RTlog(Q) because of rough estimate 2.3logX=linX 2. at equilibrium, there isn't an available free energy which means delta G is zero. so plug zero for G and equation will be ΔG⁰=-RTln(K). it is necessary to find a new ΔG⁰ or K when the temperature changes. When Q is 1, RTln(Q)=0 which means delta G is equal to ΔG⁰ Relationship Between K and ΔG⁰ using equation ΔG⁰=RTln(K): 1. if K=1 then ΔG⁰=0 2. if K>1 then ΔG⁰<0 3. if K<1 then ΔG⁰>0 --this shows that if a reaction has an equilibrium constant greater than 1, the reaction is spontaneous at the temperature and so forth

Free Energy and Chemical Energy. Also Nernst Equation.

--standard state emf or cell potential (E) or electromotive force can be found from the cell diagram --from the diagram, the potential of reduction half reaction of left side at anode is subtracted from potential of reduction halt reaction of right side at cathode --positive cell potential indicates a spontaneous reaction based on Delta.G=-n*F*E.max which can be applied to galvanic cell with standard conditions --n is the number of moles of electrons that are transferred --F is the charge on one mole of electrons which is typically (96,486 C mol-1) --E is the voltage --this means the total charge of n*F*E represent the product of free energy --when Delta.G is negative, it means work is being done by the system --when Delta.G is negative, F is positive because it is a constant and n can only be positive, E.max or voltage must be positive --with voltage positive, the reaction is spontaneous --but E can be negative which makes delta G positive Nernst Equation: --this equation is derived from the substitution between DeltaG.not=-nFE.max and DeltaG=DeltaG.not+RTln(Q) --you will eventually get E=E.not-[RT/nF]*(logQ) --it can also be rewritten as E=E.not-[0.06/n]*logQ at 298K and in base 10 logarithm --Nernst equation allows nonstandard concentrations to be plugged in in order to create Q and find cell potential --the equation expresses the relationship between chemical concentrations and potential difference (even for resting potential)

State Functions

--state is defined as the physical condition of a system --state can be number of moles, internal energy, enthalpy, entropy, and Gibbs energy. Or pressure, temperature, and volume --properties that describe the current state of a system is called state functions which is observable --ex. There are two cups of the same volume of water at 25C. but one cup is heated while the other is chilled shows differences in appearance making temperature a state function. --overall, state functions are pathway independent and describe the state of a system which is the change in a state property going from one state to another (see what changed it). --path function describes the pathway used to achieve that state of a system --work and heat are examples of path function or thermodynamic functions but not state functions. --remember, thermodynamic functions cannot be applied to systems on a molecular scale or microscopic level that shows the motions of individual molecules within a system --microscopic level however can be related to thermodynamic functions by statistics. Statistical predictions are like increasing the number of times a coin is flipped in order to get a more accurate number of heads achieved or approaches to 50% of the total. --but when sample size is far too small, predictions can be less reliable. In other words, thermodynamic functions apply to systems with large numbers of molecules. --Recall... State function are internal energy (U), temperature (T), Pressure (p), volume (v), enthalpy (H), entropy (S), and Gibbs energy (G).

Finding the pH

--strong acids and bases dissociate almost completely in water --when the reactants of acid or base is dissociate to have almost zero concentration, the products such as H3O and OH will become to have the same original concentration of acid or base Example... Acid--> given 0.01 mol L-1 of H3O. so 0.01=10^-2 and log(10^-2)=2 so pH is 2 Base--> given 0.01 molar solution of NaOH, the pOH is equal to 2 meaning pH is equal to 12 Solving Acid-Base reactions: 1. write out reaction equations for both acid and base separately ex. HCN+H2O⇌H3O+CN so K.a=[H3O][CN]/HCN 2. once you know the equilibrium constant, it can be used to have how much of HCN was dissociated given 0.01 moles of it was added to one liter of pure water ex. K.a=[x][x]/[0.01-x] 3. MCAT you can only approximate so x=√6.2x10^-12 which is roughly 2.5x10^6 or about half --this means pH of the solution is between 5 and 6 since -log(2.5x10^-6) is between 5 and 6 --therefore, this pH is a reasonable for a dilute weak acid --the process is the same for K.b --also substract pOH from 14 to find the pH and see if this is reasonable for weak base

First Law of Thermodynamics

--the first law states the total energy of the system and surroundings is always conserved Equation--> Delta.E=q+w --q represent the sum of heat flow into the system --w is the work done on the system --the first law can rewrite this type of formula to Delta.U=q+w where U stands for internal energy --internal energy comes to play since it can only be the reason for energy change in a closed system with no electric or magnetic fields --the only time work is not included in to the equation (delta.U=q) is when the reaction within a system involves no change in volume as well --when energy is transferred away from the system (as in expansion wince energy transfer tend to be accompanied by change in volume), the work done is viewed as negative --when energy is transferred into the system (as in contraction), work is seen a positive --easy to remember; expansion means decrease in energy so delta E value is negative --for mcat sake, remember the tip that energy transfer into the system during contraction volume(work) is positive --keep an eye on how MCAT question passages are worded; work done ON the system is positive while work done BY the system is negative (so E=q-w) --similar logic to heat when heat transfer from warm to cool system (heat leaving warm system is neg) --but increase temperature leads to increasing internal energy

Nomenclature and Physical Properties of Aldehyde and Ketones

--the one in ketone indicate the position of the carbonyl in the carbon parent chain --no number is necessary in the name of aldehyde because aldehydes are always terminal functional group --aldehyde and ketones are more polar so it is soluble in water and higher boiling points --they can't with each other but aldehydes and ketones can form hydrogen bonds with water and other compounds (compounds with an H attached to F, O, or N) --both of them exists at room temp as tautomers which can be generated when the alpha-carbon attached to carbonyl is deprotonated while the oxygen of the carbonyl is protonated ex. is Keto-Enol Tautomerization **Link: https://chem.libretexts.org/Bookshelves/Organic_Chemistry/Map%3A_Organic_Chemistry_(Vollhardt_and_Schore)/18%3A_Enols_Enolates_and_the_Aldol_Condensation%3A_ab-Unsaturated_Aldehydes_and_Ketones/18.02%3A_Keto-Enol_Equilibria Tautomers: --producing a tautomer can be speed up using a catalyst (either an acid or a base) --tautomers do not have resonance structure or movement --keto-enol tautomerization is a form of tautomerization which is an equilibrium reaction and not a resonance --watch for the proton shift and expect this on MCAT Enolate: --it is a negatively charged enol or enol without a proton on the alcohol --in other words, it is a basic carbonyl that attacks itself internally (from the negatively charged alpha carbon to the C=O) --there are two kinds of enolate; Kinetic and Thermodynamic --Kinetic Enolate is formed by removing one of the acidic alpha hydrogen (C=O) so the oxygen bonded to the carbonyl has a negative sign (C-O) making oxygen have too many electrons and carbon is double bonded with another carbon instead --Thermodynamic Enolate is more difficult to form due to its higher activation energy --Thermodynamic enolate has a very similar structure as kinetic such as negative sign oxygen and carbon double bonded with another carbon instead --the difference between them is very slight, while kinetic has a carbonyl with a double bond with the end carbon, thermodynamic has a carbonyl double bonded with third, fourth etc internal (not the last) carbon --this is why Thermodynamic is amore substituted enolate than kinetic --overall, kinetic has a lower activation energy and forms less stable product while thermodynamic is the opposite (requires high heat or temp.)

Phase Changes and Heat Curve Diagram

--typically start with ice at -10C --heat is uniformly added at a constant rate and the energy entering the ice increases the vibration of its molecules --this increases kinetic energy and raising temperature --ice reaches 0C and temperature stops increasing but heat is still flowing in. at this point hydrogen bonds weakens and breaks --so the ice becomes liquid water --temperature begins to rise again when heat is added --the water reaches 100C or boiling point and the temperature stops rising again, allowing energy to break more hydrogen bonds and molecules movement increases --at this point liquid is transitioning to gas phase --overall, at 0C (melting point) and 100C (boiling point), no change of temperature occurs but phase change is completed --while temperature remain constant at 0C or 100C, energy is transferred in as heat at constant pressure 1 atm --since pressure is constant, q=H --enthalpy change associated with melting is called heat of fusion --enthalpy change associated with boiling is called heat of vaporization --different compounds have different heats of fusion and heats of vaporization based on how tightly the molecules are held together within the compound --heat of vaporization is usually larger than heat fusion because it takes more energy to be added to break intermolecular bonds while there more energy released when bonds are formed --on a phase change graph, the y-axis represent temperature (T) while x-axis has heat (q) --the line slope increasing upward can be solved for heat using q=mc*delta.T --when line slope is plateau or straight line, it is solved as enthalpy (heat of fusion going from solid to liquid phase or heat of vaporization going from liquid to gas) --slope can be solved in general as 1/mc **view below for more info** Each Phase of a Substance Has its Own Specific Heat: --ex. ice to water has a heat of fusion of 0.33 kJ/g while from water to steam the heat of vaporization is 2.26 kJ/g --heat curve graphs will have temperature (T=[1/mc]*q) on the y-axis and heat on the x-axis (q=mcdelta.T) --when temperature is rising, the slope is equal to the inverse of specific heat times the mass (1/m*c) --each phase has a unique slope because of unique specific heat --since gas molecules are so dispersed, gas tend to have much lower specific heat because of lack of intermolecular forces Names of Phase Changes: --solid to liquid= melting (entropy and enthalpy positive) --liquid to solid=freezing --liquid to gas=vaporization (entropy and enthalpy positive) --gas to liquid=condensation --solid to gas=sublimation (entropy and enthalpy positive) --gas to solid=deposition

Factors that Affect Solubility

--what affects solubility is pressure and temperature --gas or solute solubility decrease when increasing temperature since it pushes the reaction to the left --this is why applying the Le Chatelier's principle should be used as caution --however, it does occur that water solubility of many solids increase with increase temperature regardless of enthalpy change --it is because with large increase of entropy (positive) by the impact of high temp and resulting in a ore negative Delt.G and thus a spontaneous reaction according to G=H-T*S ex. is salt when it is introduced to heat --but this is not the case when it comes to gas dissolving into liquid because entropy is no longer positive --another factor is gas's size and reactivity with the solvent --heavier or larger the gas, greater impact by van der Waals forces making it soluble --also gas that chemically react with solvent have greater solubility --pressure may have little effect on solubility of liquid and solids --but it can increase solubility of a gas --according to Henry's Law... C=k.a1*P.v where C is solubility of a gas (moles/liter), P.v is the vapor partial pressure of gas above the solution, and k.a1 is Henry's law constant which is unique to each solute-solvent pair --the law can also be rewritten as P.v=X.a*k.a2 where X.a is the mole fraction of a molecule "a" in a solution --the equation shows that vapor partial pressure is proportional to concentration of a gas in solution --recall Raoult's Law...PV=X.a*P.a --this law does not agree with Henry's Law --but Raoult's law is more accurate when you apply vapor partial pressure of a solvent with high concentrations --Henry's law is accurate when you apply vapor partial pressure of a solute where solute has low concentration --basically Henry's law is about solubility of a gas that is proportional to vapor partial pressure **in ideally dilute solution, the solvent (more than two molecules) obeys Raoult's law while solute obeys Henry's law** **overall, both equations do show that partial pressure of a solution is always proportional to mole fraction (X)** Raoult's Law vs. Henry's Law Diagram: 1. Raoult's Law --> when there is a container of only volatile (easily evaporate at normal temp) solvent particles, more gas molecules are formed. this means vapor pressure increase --when you had nonvolatile solute particles in the solvent, there is decrease of gas and decrease in vapor pressure --therefore, partial vapor pressure (pressure by individual gas in a mixture of gases) is equal to the vapor pressure (pressure by vapor on its condensed form such as liquid or solid) 2. Henry's Law --> container filled with solution and solute is initially at equilibrium of solubility (meaning same rate of making gas particles and making liquid particles) --when pressure increase, more molecules dissolve and less gas are made --meaning pressure increase solubility --eventually equilibrium will be reached --therefore, partial vapor pressure is proportional to Henry's law constant

Equilibrium

--when chemical reactions reverse to some extent, the rate of the forward reactions usually begins to slow and the rate of the reverse reaction quickens --as reactants convert to products, the reactant concentration decreases as the product concentration increases --when the forward reaction rate equals to the reverse reaction rate, it is called chemical equilibrium --at equilibrium, there is no net change in the concentration of products or reactants ex. the game eventually becomes equilibrium since side one, there are more players and fewer balls to throw. so more time is required to find a ball to throw and the rate of ball throwing slows down. but on side 2 there are more balls and the grab and throwing is quicker. but the rate equalizes where there is no winner. --on a graph, a curve looks like an upside down smile showing the point of equilibrium located at the maximum or greatest overall entropy (top of the curve) --it is equilibrium in the middle between the left side of the graph (all of reactant reaction) and the right side (all of product reaction). --at equilibrium there is a mixture of both reactants and product --it can be represented as aA+bB-->cC+dD where at equilibrium there will be some of A, some amount of B, some amount of C and etc in the reaction flask --to determine the relative amount of each species, use the equation K=([C]^c*[D]^d)/([A]^a*[B]^b) or (products coefficient/reactants coefficient) --K represent equilibrium constant which is a unitless value because the concentrations are approximations --Law of Mass action is the relationship between chemical equation and equilibrium constant --K will not change unless the temperature changes --remember capital K is equilibrium constant while small k is rate constant --at equilibrium net reaction rate is zero and rate can be determined by rate=(-1/a)*([A]/t) --overall, pure liquid, pure solid or ideally diluted solvents will have a value of 1 for equilibrium expression which means they do not contribute to value of equilibrium constant (K) --this also mean their mole fraction is one and the amounts may change but concentration do not

Work

--work is any energy transfer that is not heat and transfer is due to force --work tends to change the motion or positions of a body --there are two types of work when a chemical system is at rest 1. PV work--> at rest, system has changing size or shape while its position stays the same 2. Non-PV work--> most important form is electrical work --when a system does the work on the surrounding, that work is negative since energy is being transferred out of the system --you can determine pressure P=F/A and using pressure can determine work by W=-P*Delta.V but under constant pressure --by adding or removing one mass changes the pressure which allows the piston to rise or be lowered --pressure 2mg/A if increased --work is also a path function, a different pathway results in a different amount of work --in this case, work is equal to mgh --usually a pressure on the y-axis and volume on the x-axis graph shows how the magnitude of the work done is equal to the area under the curve --area is different under the curve dependent on the pressure increase or decrease --the way the curve flows or its direction represent work since work is a path function (to the right and up and down) --essentially, it is the directional collisions between molecules that distinguishes between work and heat --ex, molecules for work bump to the molecules of the surroundings in the up direction all only

Absorption and Emission Line Spectra

=(--energy is released when excited electrons fall from higher to lower energy state --when energy is released, it creates an emission line spectrum (a characteristic of a given element) --while absorption line spectrum measures the radiation absorbed when electrons absorb energy to move to a higher energy state --Max Planck proposed a theory to this phenomenon by explaining how energy change and quantification comes in discrete increments or units --Think about the equation DeltaE=h*f where h is Planck's constant (6.6 x 10^-34 J S) and f is frequency --Einstein proposed how energy of a single photon is DeltaE.photon=h*f --Louis de Broglie expanded the idea of wave characteristics of electrons and other moving masses around the nucleus: λ=h/(m*v) where v is the velocity --energy levels of an electron can be represented as an energy ladder --electrons can occupy any rung (steps) on a ladder but cannot occupy the space between rungs because the space is forbidden energy levels --when electrons move from higher to lower rung, energy from the atom is released in the form of a photon --photons have wave frequency which is related to the change in energy like how its stated in E=h*f --photon collides with an electron to bump it to another energy level if only the energy matches to the energy difference between rungs --if the photon does not have enough energy to cause electron to move higher rung, the electron would remain in the same rung and photon is reflected away

Real Gases

A real gas is a gas that does not behave as an ideal gas due to interactions between gas molecules. --under the condition of high pressure and low temperature, the volume of the molecules becomes significant --the high pressure is what deviates from ideal behavior because the molecules they push gas molecules together --the molecules get so compressed that the distance between them is similar to the distance between molecules in liquid state making the force also become significant --the pressure level to deviate from ideal gas is above 10 atm --deviation can be expressed quantitatively by Van der Waal's equation: [P+(a*n^2)/(V^2)](V-n*b)=nRT --this formula solves for real pressure and real volume of a gas when 'a' and 'b' are constant for specific gas --'a' and 'b' generally increase with the molecular mass and molecular complexity of a gas --'a' represent the strength of the intermolecular attractions while 'b' reflects the actual volume --the equation is provided on the MCAT but it is better to understand it --molecules of real gas do have volume and their volume can be added to the ideal volume which means V.real is greater than volume of ideal --accounting the size of the molecules tend to increase the overall volume of the container making the intermolecular forces to decrease --the number of molecules stay the same but they have larger size in a larger volume --V.ideal can be calculated from PV=nRT (ideal gas law equation) --molecules in real gas do exhibit forces on each other since they are most attractive --in fact, gas molecules are pulled inward toward the center and move slowly before colliding with the container wall --so the molecules strike the wall with less force and viewed by ideal gas law that real gas exerts less pressure than ideal gas P.real < P.ideal where P.ideal can be calculated from PV=nRT --remember, on the MCAT, most gases can be considered to be ideal unless it is instructed otherwise Deviation from Ideal Gas Law Graph: --on the y-axis is PV/RT --on the x-axis is the pressure --slope line represent individual gas (ex. H2, CH4 or N2) --PV/RT equals to n=1 or one mole of an ideal gas at any temperature and pressure --but volume changes when it comes to deviating from Ideal gas law --when PV/RT is greater than one, deviation due to volume must be greater than the deviation due to intermolecular forces --in other words, pressure value increase as PV/RT increase --when PV/RT is less than one, the deviation due to intermolecular forces must be greater than deviation due to molecular volume --essentially, PV/RT is negative or deviation is negative as attractive intermolecular forces or pressure still increase **overall, how can ideal behavior deviations occur when increasing pressure also increase temperature? Well it is resulted from any situation in which molecules move closer together or when volume is decreased** **volume can be decreased by squeezing the molecules together with higher pressure or by lowering the temperature** **based on PV=nRT, pressure can increase when volume decrease or volume decrease when temperature decrease**

Alcohol: Nomenclature, Physical Properties and Reactions

Alcohol--> consists of an oxygen bound to a hydrogen and an R group --alcohols commonly act as nucleophiles and its boiling point of alcohols goes up with molecular weight --but the boiling point goes down when there are more branches --boiling and melting points of alcohols are much higher than their similar size alkanes due to their ability to hydrogen bond --since hydrogen bonding increases intermolecular forces --alcohols are also considered an electron-donating group when it attacks a positive or partial positive charge --alcohol can act as acids since one of the covalent bond of the oxygen is bound to a hydrogen --but this bond is a weak bond making it easy to lose its proton (H+) --alcohols are not particularly good leaving groups because they are reactive in solution --but it can easily be protonated by other stronger molecules which makes it into water and water is a much better leaving group because of its stability **overall, alcohol act as an acid when O-H bond is broken. but alcohol acts as a leaving group when it breaks C-O bond** Alcohol Undergo Three Major Types of Reactions: 1. most important to know for Mcat is that alcohol acts as nucleophiles 2. they act as acids since it loses their hydrogen. essentially, alcohols attack carbonyls and loses their proton 3. protonated alcohols act as leaving groups

Periodic Trends

Atomic Radius: increases going down and to the left on the periodic table --it is the distance from the center of the nucleus to the outermost electron or the size of the atom --elements to the right have additional protons that pulls surrounding electrons more strongly --going down the periodic table represent elements having new and more shells of electrons which shields the attraction of protons from the inner nucleus Electrostatic Force: is the force between charged objects which is the attraction between opposite charges and repulsion between same charges --consider Coulomb's law F=k*q1*q2/r^2 --r represent the distance between electron and nucleus --q1 and q2 are the charge of electron while Z is the charge of the nucleus --Z.eff is the effective nuclear charge which is the amount of added electron to an atom --in Coulomb's law, Z.eff is plugged in for q1 to find the force on the outermost electron --essentually the force on an electron is a function of both q1 (Z.eff) and r --since Z.eff can be used to explain atomic radius, more electron added encourages atom to get smaller since electrons are getting pulled closer to the nucleus meaking Z.eff smaller and shielding increases --so Z.eff would be 1eV for each electron --every time electron is added, it is shielded so it won't experience the full attractive force of all the protons in the nucleus --Z.eff generally increases going left to right across the periodic table --Z.eff also increase going from top to bottom down the periodic table --Z.eff value drops when new electron is added to an entirely new shell since this cause increasingly strong shielding Ionization Energy: increases as going up and from left to the right of the periodic table --it is the energy needed to detach an electron from an atom - holding the outermost electron more tightly increases ionization energy --when electron is too strongly attracted to the nucleus, more energy is needed to detach it --first ionization energy is energy required to remove an electron from neutral atom in its gaseous state to form +1 cation --second ionization energy is removal of second electron from same atom to form +2 cation making this greater energy than the first --same situation for third, fourth, fifth and so forth ionization energies Electronegativity: increases as going up and to the right of the periodic table --it is the tendency of an atom to attract electrons shared in a covalent bond --two atoms with different electronegativities will share electrons unequally which causes polarity --atoms with greater Z.eff will pull more strongly on electrons in covalent bonds which increases electronegativity --electronegativity is measured by Pauling Scale (ranges from a value of 0.79 for cesium to 4.0 for fluorine) --fluorine is the most electronegative element --between hydrogen and carbon (CH4), carbon will carry a partial negative charge while hydrogen carries a more positive charge --electronegative values help predict which type of bonds will form --ex. atoms with large differences in electronegativity (1.6 or larger on Pauling scale) will form ionic bonds. like metals and non-metals --atoms with moderate differences (0.5-1.5 Pauling scale) will generally form polar covalent bonds --atoms with minor electronegativity differences (0.4 or smaller on Pauling scale) will form nonpolar covalent bonds Electron Affinity: increases as going up and to the right of the periodic table --is the willingness of an atom to accept an additional electron --some atoms release energy when accepting an electron which makes them more stable while other atoms require energy input to force an addition of an electron (this decreases stability) --electron affinity is more exothermic to the right and up on the periodic table --noble gas does not follow this trend since electron affinity for this is endothermic since noble gas is stable and significant amount of energy are required to form them to take on electron and become less stable --also atoms with stronger Z.eff will accept another electron so electron affinity increases

Bonds and Hybridization

Atoms can form multiple bonds. Example is a carbon that can have single (CH4), double (C2H4) or triple bonds (C2H2). Multiple Types: 1. Sigma Bond (σ)--> it is where hybrid orbitals of two atoms overlap. it is the lowest energy, more stable and strongest type of covalent bond. It is always the first type of bond to form between two atoms, so a single bond. It can also be double and triple bond since it is a covalent bond localized directly between two atoms. but there will only be one sigma for double and triple bonds 2. Pi Bond --> it is where p orbitals overlap. when there are double and triple bonds, pi bonds is accompanied with sigma bonds. sigma bonds leaves no room for other electron orbitals (like pi bonds) directly between atoms. So the pi bond will need to be located above or below the sigma bonding electrons. this means every double bond consists of one pi and one sigma bond. similar to triple bond, adding another pi bond means locating it on either side of the sigma bond. this creates one sigma bond and two pie bonds for triple bonds **pi bonds are weaker and more reactive than sigma bond so less bond energy required to break pi bond** **bond energy increases as more pi bond is added to sigma bond** **at the same time, adding pi bonds shortens the overall bond length** **therefore, single bonds are the longest and easiest to break and triple bond is the shortest and most difficult to break** **atoms bound by single bonds can rotate freely around the bond while adding pi bonds hinder free movement by locking atoms in place and introducing rigidity in molecular structure** Hybridization & Molecular Shape (Hybrid Orbitals): 1. sp with a bond angle of 180 degrees making a linear shape 2. sp2 with a bond angle of 120 degrees with a trigonal planar shape 3. sp3 with a bond angle of 109.5 degrees with a tetrahedral, pyramidal or bent shape 4. sp3d with a bond angle of 90 or 120 degrees with a trigonal-bipyramidal, see-saw, t-shapes or linear shape 5. sp3d2 with a bond angle of 90 degrees with a octahedral, square pyramidal or square planar shape ex. H2O or H-O-H has two lone pairs and two sigma bonds making S^1 P^3 or SP3 equaling 4. Valence Shell Electron Pair Repulsion (VSEPR) is a theory about electrons in an orbital wanting to move far away from other electron pair as possible in order to reduce their energy and minimize repulsive forces. This is why there are specific angles. Crash Course: https://www.youtube.com/watch?v=cPDptc0wUYI https://www.youtube.com/watch?v=hEhUNikSC90

Solubility and Solubility Guidelines

Ba (aq)--solubility quantifies solute's tendency to dissolve in a solvent --it is measured in mol/L --solute will usually be a salt --solvent will usually be water --when dissolution of a salt is reversed, it means salt particles in solution re-attach to the surface of the salt crystal --crystallization is exothermic --precipitation is this reverse reaction which is lower rate than the rate of dissolution at first --but as the concentration of dissolved salt increase, the rate of dissolution and precipitation equilibrate --at equilibration, the solution is saturated since the concentration of dissolved salt reach maximum --also the forward and reverse reactions continue to occur at equal rates while the product and reactant concentrations do not change --equilibrium of a solvation reaction has its own equilibrium constant known as solubility product K.sp --given a reaction, solubility product excludes solids ex. Ba(OH)2 (s) ⇌ Ba (aq) +2OH (aq) to equilibrium constant K.sp=[Ba][OH]^2 --remember solubulity product is a constant while solubility is the maximum number of moles of a solute that dissolve in a solution --solubility product is fixed for a given temperature while solubility depends on both temperature and ions in solution --spectator ions are ions like Na+ that are not included in the equilibrium expression since they have no effect on the equilibrium --ions that do affect the equilibrium is also included in the equilibrium expression which is known as common ion effect --common ion effect disturb the equilibrium since it involves an ion in common with an ion in the equilibrium expression --including a common ion pushes the equilibrium to the direction that will reduce the concentration of that ion ex. BaF2 (s) ⇌ Ba (aq) + 2F (aq) --in this case, equilibrium move to the left in order to decrease concentration of F meaning reducing solubility of BaF2 --although common ion added to a saturated solution shifts the equilibrium and increases amount of precipitation, it does not affect the solubility product --for MCAT, all ionic compounds containing nitrate (NO3^-), ammonium (NH4), and alkali metals (LI+, NA+, K+) are soluble --insoluble compounds, by themselves, are carbonates (CO3^2-), hydroxides (OH), phosphate (PO4^3-), and sulfides (S^2-) --it is unlikely that the MCAT will have you know these rules (and more) --but the big take away is to pay attention to charge and size --ionic compounds composed of cation or anion that have a single positive and negative charge are usually soluble --so compounds containing 2+ cations are less likely to be soluble --smaller ions or molecules are typically soluble while compounds containing large, heavy cations are less soluble

Calorimetry

Calorimeter--> measures heat change --it is a container that holds a liquid with a thermometer placed inside to measure any change in temperature --it is highly insulated from the surroundings --lets say an endothermic reaction takes place inside a water filled calorimeter --the reaction requires heat from the surroundings --but since the calorimeter is insulated from the environment, all the heat will come from the water --so the temp of the water will diminish and the heat transfer away from the water as well as the temperature change can be solved using the formula q=mcdelta.T Two Types of Calorimeters: 1. Constant Pressure Calorimeters --> an example is a coffee cup calorimeter which uses an insulator to prevent heat exchange with its surroundings --a thermometer is used to measure the change in temperature --it does not contain expanding gases which ensures heat reactions take place inside them --you can measure heat reaction or enthalpy (Delta H) by plugging delta H for q in q=mc*delta.T since H=q at constant pressure --H reaction is negative of q because heat transferred into the calorimeter (positive) is equal to the heat released by the reaction (negative) --if the value G is given, the change in entropy (S) can be solved by substituting the into the equation G=H-T*S 2. Constant Volume Calorimeters --> example is a bomb calorimeter which measures energy change at constant volume --in other words, it measures the internal energy change in a reaction --the bomb calorimeter consists of a rigid container inside a thermally insulated container --unlike the coffee calorimeter, the heat is released to the surrounding liquid and inner container when a reaction occurs --internal energy change can be determined using q=C*delta.T

Solution Concentration

Five Ways to Measure Concentration of a Solution: 1. molarity (M) --> M=(moles of solute)/(volume of solution) 2. molality (m) --> m=(moles of solute)/(kilograms of solvent) 3. mole fraction (X)--> X=(moles of solute)/(total moles of all solutes and solvent) 4. mass percentage--> %=(mass of solute)/(total mass of solution)x100 5. parts per million (ppm) --> ppm=(mass of solute)/(total mass of solution)x10^6 --ppm is the mass of solute per mass of solution times 1 million Normality: measures number of equivalents per liter of solution --most likely appear in the context of acid-base reaction --for this reaction, equivalent is defined as mass of acid or base --ex. 1 molar solution of H2SO4 is called a 2 normal solution because it can donate 2 protons for each H2S04 molecule

Covalent and Ionic Bonding

Covalent Bond: --electrons shared between atoms --atoms held by covalent bonds form a molecule --covalent bonds are formed only between nonmetal elements --this kind of bond is a predominant type of bond --the attractive and repulsive forces due to charges achieve a balance to create a bond --as the bond length or internuclear distance grows, the potential energy also increases from negative value to zero --two atoms will form a bond when the atoms lower their overall energy level since nature seeks the lowest possible energy state --which is why energy is released when bonds are formed --nonpolar covalent bond is when electrons are shared equally by two atoms --polar covalent bond, on the other hand, is when electrons are not shared equally due to differences in electronegativity --overall energy is released when new bonds formed and not when bonds are broken (energy absorbed) Ionic Bond: --electrons transferred from one atom to another --keep in mind, the distance between the nuclei of two atoms in a bond at their lowest energy state is known as bond length --when the distance between the bond of the atoms separate further by an infinite distance, the force between them and energy of the bond becomes zero --the energy necessary for complete separation of the bond is known as bond dissociation energy or bond energy --if the difference in electronegativity is significant, then the bond is partial ionic character --vastly different electronegativity between two atoms is known as ionic bond --this occurs between metals and nonmetals --ionic compounds or salts is seen as oppositely charged ions join together by electrostatic forces

Carbonyls as Nucleophiles: Aldol Condensation

Cyanohydrins--> this is produced by nitriles acting as a nucleophile. it consists of nitrile (CN) and alcohol that are attached to the same carbonyl carbon Phosphoric Acid--> it is related to carbonyl in a way that P=O bond is polar with P holding partial positive charge like carbonyl carbon --like carboxylic acids, phosphoric acids can form anhydrides and esters that can be hydrolyzed (break down) with water --know the general structure of phosphoric acid for MCAT [O=P-OH (3x); meaning P is connected to three bonds of OH] --also phosphoric anhydrides are formed when phosphoric acids are heated and esters are formed when phosphoric acid reacts with alcohol --phosphoric anhydride bonds are relatively high in energy and serve as a major form of energy in the cell as ATP Aldol Condensation: carbonyl nucleophile attacks another carbonyl --typically the alpha carbon can act as a nucleophile --it forms new bond between the alpha carbon of one molecule (preserving its carbonyl) and the carbonyl carbon of another molecule (reduced to an alcohol) --aldol name means ald from aldehyde and ol from alcohol --the condensation occurs when aldehyde reacts with another, when one ketone reacts with another or when an aldehyde reacts with a ketone --the condensation reaction can be catalyzed by an acid or base --when a base is around, it removes alpha hydrogen and leaves an enolate ion which acts as a nucleophile --enolate ion is essentially the original molecule but with a missing hydrogen ex. R-CH2-C=O-H + OH- makes R-CH=C=O-H --enolate ion then acts as a nucleophile which attacks carbonyl carbon of the other aldehyde or ketone to create alkoxide ion which is basically a bond of enolate ion with original molecule ex. R-CH2-C-O-H (carbonyl carbon C-O of original) connect with R-CH-C=O-H (carbon of C-H that no longer is double bonded with CO of enolate) --since the alkoxide ion is a stronger base than hydroxide ion OH, so it will acquire an electron or H- from the water to the C-O of alkoxide ion making aldol --since aldol is unstable, it can by dehydrated (removal of OH) by heat or base to make enal --enal is an aldehyde with an alkene at the beta carbon (meaning COH lost OH and creates a double bond with the carbon next to it --through out this reaction, the condensation part only takes place when aldol gets dehydrated to become enal and condensation is always occurred after aldol addition (first part of the reaction) --aldol condensation is one of the reaction of glycolysis and the reverse reaction of this is called retro-aldol which is when ATP activated glucose is split in half --overall, when you notice the attached function to the carbonyl carbon is changed, this usually means the carbonyl carbon was attacked by a nucleophile which is either an addition or substitution reaction --addition keep in mind is aldehyde or ketone becoming alcohols --substitution reaction is carbonyl with a new leaving group --if the original carbonyl carbon is intact or preserved with a new bond to the alpha carbon, then the carbon is the nucleophile --if this occurs, think of carboxylate or enolate ion of aldol condensation

Other Ways to Represent Molecules

Dash Formula--> shows the bonds between each atom of a molecule but does not display lone electron pairs or show three-dimensional structure of the molecule ex. H-C-C-C-O-H Condensed Formula--> shows neither bonds nor three-dimensional structure ex. CH3CH2CH2OH Bond-Line Formula--> appear as intersecting lines, corners and endings representing carbon atom connecting to a functional group such as -OH. hydrogen atoms do not appear attached to the ends or corners of the lines representing carbons ex. \/\/OH Fischer Projections--> most common on the MCAT which appears as a vertical line (oriented into the page) and horizontal lines (oriented out of the page). used to represent carbohydrates and provide 3-D shape of a molecule Newman Projection--> consists of intersecting lines through and out from a large circle. it provides information of steric hindrance. ex. https://www.chemistrysteps.com/newman-projections/ Dash-Line-Wedge Formula--> consists of solid black wedges representing bonds coming out of the page. dashed wedges indicate bonds going into the page on the lines Space-Filling Model--> 3-D representation of a molecule with spheres or various colors. the different colors indicate different elements of various sizes Ball and Stick Model--> this model give details about relative size of atoms by drawing to scale atomic radii for atoms. but, bond lengths are drawn about twice the length so the atoms are clearly visible ex. https://stock.adobe.com/images/vector-ball-and-stick-model-of-alcohol-substance-icon-of-methanol-or-methyl-alcohol-molecule-consisting-of-carbon-hydrogen-and-oxygen-structural-formula-suitable-for-education-isolated-on-white/302317729

Ethers vs. Ester

Ester: --alcohols convert to ester called a sulfonate --this is a good form of a leaving group than alcohol because of how weak of a base it is --because it is a base, it can distribute negative charge --so sulfonate does not need to be protonated like alcohol in order to be a good leaving group --commonly used sulfonates are Tosylate and Mesylate --tosylate and mesylate are useful for the protection of alcohols by preventing alcohols from acting as an acid which is reactive --sulfonate can be converted back to an alcohol Ethers: --Ether is often the solvent of choice on MCAT since it is relatively unreactive --if it does show up, it could be a substitution reaction or cleavage of the ether by HI or HBr to form alcohol and alkyl halide --one of the two R group from ether is protonated by HI or HBR to make RBr and the hydrogen from the attacker is attached to the left over OR to make ROH. --it isn't reactive and it contains an oxygen with lone pairs of electrons --so the oxygen part of the ether can bond to hydrogens from other molecules that contain it such as N, O and F atom --ethers are just as soluble in water as alcohol --but it is less polar than alcohols and most organic compounds are nonpolar and tend to be more soluble in ethers than in alcohols since hydrogen bonds do not to be broken for it to dissolve --it is similar to principle that "like dissolves like."

Hydrides and Conjugate Acids and Bases

Hydrides --> compounds with only two elements (binary compounds) containing hydrogen --according to the periodic table, basic hydrides are to the left --acidic hydrides are to the right (4A, 5A, 6A, 7A groups) --metal hydrides are either basic or neutral --nonmetal hydrides are acidic or neutral (except for ammonia NH3) --the acidity of nonmetal hydrides tend to increase as you go down the periodic table (period 2, period 3 etc) Conjugate Acids and Conjugate Bases: --the rule is that if there is an acid in a reaction, then there is also a base --it is because a proton cannot be donated without another species present to accept it ex of acid and base reaction in aqueous solution --> HA+H2O⇌H3O+A where HA is the acid and water accepts the proton meaning water is the base. also, in reverse reaction, hydronium ion donates a proton to A- making hydronium ion as the conjugated acid and A= the conjugated base --so remember, the stronger the acid, the weaker its conjugated base --stronger the base, the weaker its conjugated acid --but it is incorrect to think that weak acids have strong conjugated base because it can have strong or weak conjugated base --therefore, when there's an acid-base reaction, there's always conjugated base and acid --a graph may be shown with conjugated base or acid strength on the y-axis while acid or base strength is on the x-axis --the slope starts up top of the graph and slowly declines and dips down close to the x-axis until it plateau making the line parallel to the x-axis

Systems and Surroundings

Intensive vs. extensive property: intensive is pressure while extensive property is volume --while volume is fixed, there are can be external pressure to withhold the stretching of a container --essentially, the greater of random translational kinetic energy of gas molecules per volume, the greater the pressure --thermodynamics is the study of energy Three rules or laws of thermodynamics: 1. law of conservation of energy states energy cannot be created or destroyed in an isolated system 2. second law states entropy (thermal energy/unit) of an isolated system always increases 3. third law endorses that entropy of a system approaches a constant value as the temp approaches absolute zero --thermodynamic problems typically divide the universe into the system and its surroundings --system is known as a section of the universe under study and the remainder of the universe is the surrounding --ex, a scientist may be interested in the system like kettle and water and the rest of the universe like table is the surrounding Three categories of systems: open, closed, and isolated 1. open system can exchange mass and energy with their surroundings 2. closed system can exchange energy but not mass 3. isolated system cannot exchange either energy or mass

Intermolecular Forces

Inter/Intramolecular: --intermolecular forces are much weaker than intramolecular forces --it describes how molecules interact with each other --but for intramolecular covalent bonds, it is when atoms interact with each other --intermolecular attractions are attractions between separate molecules (partially neg and partially pos) which occurs due to dipole moments --higher the attraction, stronger the dipole magnitude --overall, intermolecular bonds are broken when a compound moves from liquid to gas phase (physical change) --intermolecular forces can apply to solids as they do to liquids --ex. crystals such as ice are composed by intermolecular bonds --intermolecular forces generally insignificant in gases Dipole: --dipole moment occurs when center of a positive charge in a bond does not coincide with center of negative charge --when the center of positive charge is displaced from center of negative charge, the bond is said to have both partial and negative characters --in dipole, it is symbolized as an arrow facing from positive to negative charge --it is measured in unit of debye (D) and given in equation of u=q*d where q is the magnitude of charge at either end of the dipole and d is the distance between centers of charge --a bond that has a dipole moment is known to be polar and vice versa --but a molecule with polar bonds may or may not have net dipole moment --sum of dipole moments of polar bonds of a molecule can equal to zero and dipole moment is a vector --sum of dipole moment to be zero leaves the molecule without a dipole moment Induced vs. Instantaneous Dipole Moment: --induced occurs when a polar molecule starts a dipole in an atom or in a nonpolar molecule, by a polar molecule, ion or electric field. --essentially, the polar molecule disturbs the arrangement of electrons --the partial or fuller charge polar molecule attracts or repels the electrons of the nonpolar molecules which separates the centers of positive and negative charge --induced dipoles tend to be weaker than permanent dipoles --instantaneous dipole arise spontaneously in a nonpolar molecule --it is when electrons move about randomly and at any given moment they may not be distributed evenly or cause separation of charges between two bonding atoms --instantaneous dipoles are short lived and weak but can create an induced dipole in a neighboring molecule Hydrogen Bond --it is the strongest type of dipole-dipole interaction --recognized as not true bonds, instead intermolecular forces --although it is the strongest intermolecular force, they are still weaker than covalent bonds --occurs between a hydrogen that is covalently bound to a fluorine, oxygen or nitrogen atom --these elements are highly electronegative when bound to a hydrogen causing a large dipole moment --hydrogen has the stronger partial positive charge --hydrogen is the reason why water has a higher boiling point London Dispersion/Van Der Waals Forces --weakest dipole-dipole force between two instantaneous dipoles --all molecules exhibit this force first even when they are capable of stronger intermolecular interactions

Naming Inorganic Compounds

It is important to be able to identify the chemical structure of a compound if MCAT refers to it by name and vice versa... **remember to put a positive sign by a metal to remind yourself that the other part of the molecule is negative and the bond is ionic. negative part is strongly basic** --named after their cations and anions --transition metals capable of having different charges will name a Roman numeral in parentheses next to the name --it represents the charge ex. copper(I) or copper(II) which means it can take on a charge of 1+ or 2+ --elements with -ous like cuprous indicate Cu+ or cations with smaller charge --elements with -ic like cupric indicate Cu2+ or cations with greater positive charge --nonmetal cations have -ium at the end of the name like ammonium (NH4+) --there are as few ions to remember which is found on the Solutions lecture --anions such as monoatomic (single element) and simple polyatomic (more than one element) are given the suffix -ide ex. hydride (H-) and hydroxide (OH-) --polyatomic anions with multiple oxygens have an ending of -ite or -ate (use most oxygen) ex. nitrite ion (NO2-) or nitrate (NO3-) --if a oxygenated atom has hypo- in the name indicate less or fewer oxygen while per- means more oxygens ex. hypochlorite (ClO-) while perchlorate (ClO4-) --Acids will have a name with hydro- and -ic like hydrosulfuric acid (H2S) --similar to oxyacids, the name will have -ic if it has more oxygens like sulfuric acid --while others have -ous in the name if there are less oxygens like sulfurous acid

Activation Energy and the Effect of Temperature on Reaction Rate

Kinetics --> study of reaction rates and mechanisms --it essentially deals with the rate of a reaction as it moves toward equilibrium --kinetic products are less stable but can be formed more Thermodynamics --> deals with the balance of reactants and products after they have achieved equilibrium --many reactions have several possible products, each favored by different reaction conditions this is known as kinetic versus thermodynamics control Activation Energy --> reacting molecules must collide for a chemical reaction to occur --by certain criteria, can collisions cause reactions --it is because rate of a reaction may be much lower than frequency of collisions --one of the two requirements for collisions to initiate a reaction is activation energy --it is when the kinetic energy (energy of motion) of the colliding compounds is greater than or equal to a threshold energy -each particle is moving at different speeds and only the ones with sufficient speed will have kinetic energy needed to overcome activation energy --second requirement for collisions to start a reaction is that molecules or atoms must align in a specific way even if the particles have sufficient kinetic energy --both these criteria must be met Arrhenius Equation: k=z*p*e^(-Ea/RT) or k=A*e^(-Ea/RT) --z stands for the product of the collision frequency --p represents the steric fraction or fraction of collisions having spatial orientation --Ea is the activation energy --R is the gas constant 8.314 J*K-1 mol-1 --k is the rate constant of a reaction which can be affected by pressure, catalysts, and temperature --overall e^-Ea/RT is the fraction of collisions having sufficient relative energy --A can replace z*p --pressure typically impacts gases; higher pressure cause increase rate constant K --catalysts lower activation energy Ea which increases rate constant --rate of constant increase as temperature increase --since temperature promote particle movement and collisions with sufficient relative kinetic energy, this shows rate constant is proportional to rate of a reaction --temperature increasing rate reaction (kinetics) also increase thermodynamics or achieving equilibrium more quickly --on a graph, line curve has an area extended longer to the right of the energy of collisions. this means it pass the Ea threshold or enough energy to overcome activation energy and the area is larger showing more relative number of collisions. all this happens when temperature increases

Le Chatelier's Principle

Light + 2Ag^+ + 2Cl^- ⇌ 2Ag + Cl2 --this equation shows that light striking, lets say sunglasses, the reaction shifts to the right --product is metallic silver which darkens the sunglasses --in the absence of light, the reaction shifts to the left, decreasing the metallic silver and lightening the glasses Le Chatelier's Principle: states that when a system at equilibrium is stressed, the system will shift in a direction to reduce that stress -- by reducing a substance that has been added, replace a substance taken away and so on Three Types of Stress: 1. additional or removal of a product or reactant --when a solution is concentration or diluted, equilibrium shifts to the side with fewer moles when the other side of the solution is crowded 2. changing the pressure or volume of the system --if the size of the container reduced at constant temperature, total pressure increases --typically molecules move from areas of large to low amount of molecules which result in producing heat and raising product concentration 3. heating or cooling the system. heat can be thought as a product of the reaction ex. N2(g)+3H2(g)-->2NH3(g)+Heat --when temperature rise (similar to adding product), the reaction is pushed to the left --then the partial pressure of N2 and H2 increase while the concentration of NH2 decrease --similar to the right direction reaction, as N2 and H2 concentration increase, partial pressure of them reduce --NH3 and heat are generated in the forward direction as H2 and N2 are used up and its partial pressure reduced **overall, the principle does not always predict the correct shift. By adding He to a container of N2, H2, and NH3 the total pressure increases but there is no shift in equilibrium --He also did not change the partial pressure of the other gases since equilibrium did not shift

Types of Reactions

Physical Reaction --> compound undergoes a reaction and maintains its molecular structure and identity ex. melting, evaporation, dissolution and rotation of polarized light Chemical Reaction --> compound undergoes a reaction and changes its bonding or structure to form a new compound. it is typically represented by a chemical equation (CH4+2O2 ⇌ CO2+2H2O). Notice the equation is balanced since there is same number of oxygen, hydrogen and carbon on both sides. ex. combustion (burning), metathesis(exchanging ions) and redox On the MCAT it will tell you otherwise if an equation isn't balanced. Four Important Reaction Types: 1. Combination A+B->C ex. Fe+S->FeS 2. Decomposition C->A+B ex. 2Ag2O->4Ag+O2 3. Single Displacement (or Single Replacement) A+BC->B+AC ex. Mg+2HCl->MgCl2+H2 4. Double Displacement (or Double Replacement or Metathesis) AB+CD->AD+CB ex. HCl+NaOH->H2O+NaCl 5. Redox ex. 2Au3+ + 3Zn -> 2Au + 3Zn2+ 6. Combustion ex. C6H12+9O2->6CO2+6H2O 7. Bronsted-Lowry Acid-Base ex. HI + ROH -> I- + ROH2+ 8. Lewis Acid-Base ex. Ni2+ + 6NH3 -> Ni(NH3)6^2+ Δ above or below arrows indicate heat is added ⇌ means reaction is in equilibrium <-> represent resonance structures (moving electrons around the structure)

Rates of Multiple Step Reactions

Rate-Determining Step --> rate of slowest elementary steps determine the rate of the overall reaction --steps after the first slow step do not contribute to the rate law ex. NO2+CO->NO+CO2 This reaction has two elementary steps: 1 (slow step). NO2+NO2->NO3+NO 2 (fast step). NO3+CO->NO2+CO2 --NO3 is made and consumed which is why it is intermediate --rate limiting step is a product that will run out first so NO which is why it is slow --since the first step is the slowest, the rate law for the overall reaction is given by this step which is rate=k*[NO2]^2 --the exponent is 2 because the rate-determining step is an elementary equation (2 of NO2), not the same at rate law --remember slow step determines the rate of molecular level because a bulky molecule makes it difficult for other molecules to react with it --keep in mind, reaction with a fast initial step will have no intermediates appear in the overall rate law Recall: --concentration of elements influence frequency of collision and rate --Link of how to write elementary step reactions...https://www.khanacademy.org/science/ap-chemistry-beta/x2eef969c74e0d802:kinetics/x2eef969c74e0d802:reaction-mechanisms/v/mechanisms-and-the-rate-determining-step --another useful tool..https://courses.lumenlearning.com/boundless-chemistry/chapter/reaction-mechanisms/#:~:text=In%20a%20reaction%20with%20a,in%20the%20overall%20rate%20law.

Oxidation and Reduction of Oxygen Containing Compounds

Reduction --> is the nucleophilic addition of a hydride ion (hydrogen or R group) to a carbonyl. this allows the addition of electrons since there is a loss of oxygen bonds. --in other words, it begins by hydrides attacking a carbonyl and hydride is negatively charged hydrogens --carbonyls in carboxylic acid and its derivatives are generally reduced first to aldehydes and then to alcohols --a carbon is reduced when it is fully saturated with hydrogen to form alkane (C5H12) --when carbon does reduce, remember it gains more C-H bonds but loses C-O bonds --LiAlH4 or LAH is used to reduce ketones, aldehydes and carboxylic acids to alcohols --NaBh4 is a weaker reducing agent which can only reduce ketones and aldehydes but not carboxylic acids or esters --ketone and aldehyde is reduced once to an alcohol while carboxylic acids require two reduction attacks to become alcohol --recall aldehyde is a carbon chain with a H-C=O at the end while Ketone is a carbon chain with CH4-C=O at the end Oxidation --> is the nucleophilic addition of oxygen or halogen to a carbon. this cause the loss of electrons since there is a loss of C-H bonds. --when carbon is eventually turned to alcohol, it can always return back to aldehyde --through oxidation, alcohol oxidize to aldehyde which then further oxidize to carboxylic acids --for MCAT purposes, assume tertiary alcohols cannot oxidize while secondary alcohols can oxidize to ketones --overall, oxidizing agents will have several oxygen while reducing agents will have several hydrogen --common oxidizing agents are K2Cr2O7, K2MnO4, H2CrO4, O2, and PCC (gentler oxidizing agent and can oxidize primary alcohols to aldehyde and secondary aldehyde to ketones) --the last important oxidation reaction is decarboxylation which is when carboxylic acid turns to carbon dioxide gas --required high activation energy and is exothermic which makes the reaction difficult to carry out --this is a key reaction you see in the citric acid cycle

Balancing Redox Reactions

Steps to Balance A redox Reactions in Acidic Solution: 1. Divide the reaction into its corresponding half reaction 2. balance the elements (besides hydrogen and oxygen) 3. add h2o to one side until the oxygen atoms are balanced 4. add H+ to one side until hydrogen atoms are balanced 5. add electron (e-) to one side until the charge is balanced ex. 2H+ + 2e- => H2 (the 2 is cancelled out and so is the charge) ex. Ag2+ + 2e- => Ag 6. multiply each half reaction by an integer so equal number of electrons are transferred in every reaction ex. 2(Au+3e->Au) 3(Cu->Cu2- + 2e-) so 6e- is canceled. 7. add the two half reactions and simplify the reaction **follow the same steps when the redox reaction occurs in basic solution. but add the same number of OH- ions to both sides of the reaction to neutralize H- ions**

Limiting Reactants and Yield

Runs to Completion --> means a reaction generates product until the supply of at least one reactant is fully depleted Equilibriums --> rate of reverse reaction is equal to the rate of the forward reaction. so the reactants are never completely used up Ex. CH4+2O2⇌CO2+2H2O --2 oxygens are needed to burn one mole of CH4 or methane --this is a 2:1 ratio --since oxygen would run out first, making it the limiting reactant --essentially limiting reactant is what will completely be used up if the reaction is to run to completion --also keep in mind that there is a 1:1 ratio of methane to carbon dioxide so burning 3 moles of methane produces 3 moles of carbon dioxide --if you can't balance an equation, it may be a redox reaction where you need to add an acid or base to the reaction to help balance it --but if the equation on the mcat is not balanced, it is not the correct answer (unless said specifically) --remember, equilibriums do not generally run to completion Theoretical Yield --> the amount of product that should be created when a reaction runs to completion Equation: (Actual Yield)/(Theoretical Yield) x 100 = % Yield --actual yield is the amount of product created by a real experiment --in other words, theoretical yield is what you expect stoichiometrically from a chemical reaction while actual yield is what you actually get

Solution Chemistry

Solution--> is a homogenous mixture of two or more compounds in a single phase such as liquid or gas --ex. is a brass which is a solid solution of zinc and copper --solution is formed when solute dissolves in solvent Solvent--> more than two compounds in a solution Solute--> less than three compounds in a solution --looking into understanding solutions and their involvement in physical and biological processes --essentially solution formation, factors that affect the ability of solids to dissolve in solution and electron transfer reactions --solution can be formed when intermolecular bonds between solvent and solute is more favorable than intermolecular bonds within solvent or solute --ex. polar or ionic solutes dissolve well in water solvent since it is also polar --when this happens, solvent to solvent bonds are broken and solvent to solute bonds are formed --nonpolar solute cannot spread out within polar solvent due to its lack of separation of charge/weak forces and polar solute have too of a strong bonds to be broken and interacted with --recall that electrons transferred from one species to another are known as oxidation-reduction reactions (redox) --also remember that increased size or charge tends to decrease solubility --solubility is calculated as K.sp or solubility constant (tendency of solubility reaction to proceed) --species with a positive charge is known as reduction --species of negative potential is oxidation --highly polar molecules are held together by strong intermolecular bonds due to partially charged ends --nonpolar molecules are held together by weak intermolecular bonds and these forces are called london dispersion forces --ionic compounds can dissolve in polar substances since cations and anions break apart and they are surrounded by oppositely charged ends --this is called solvation and example is water which is why it is a good solvent --water molecules are surrounded by ions --water has partially positive hydrogens that points toward anions while oxygen that is more negative points toward the cations --other molecules can attach to the water --something that is hydrated is said to be in aqueous phase --ions that form in aqueous solution allows the solution to conduct electricity containing many ions which is called electrolyte

Stereochemistry

Stereochemistry--> three dimensional structure of a molecule and involves what can move and what cannot in each of the molecules involved in a reaction --for instance, double bonded atoms are locked in place while single bonds are free to rotate Various Types of Isomers: --isomers are unique molecules that share the same molecular formula --or the same molecular formula but different compounds --three major types of isomers are structural (constitutional) isomers, conformational isomers and stereoisomers 1. Structural Isomers--> simplest form of isomer which has the same molecular formula but different bond to bond connectivity or different connections between atoms ex. C4H10 one can be a n-butane ( \/\ ) or isobutane that has a center carbon and three single bonds sticking out 2. Conformational Isomers--> conformers are not true isomers. it has different spatial orientations of the same molecules. for instance, at room temperature, some atoms rotate rapidly about their sigma bond. Different energy levels will change specific atom positions of the molecule or influence bond rotation. The only way to notice conformers is with Newman projection (a circle with crossover and sticking out lines) --more eclipsed, higher in energy and less stable --more staggered, low energy and more stable Images: https://www.pinterest.com/pin/614248836658792895/ 3. Stereoisomers--> two types are enantiomers and diastereomers. when the molecules have the same molecular formula and same bond-bond connectivity. --Enantiomers have the same molecular formula and connectivity but not the same molecule because they differ their configuration. remember enantiomers are mirror images of each other with opposite absolute configurations at every chiral carbon

Stoichiometry

Stoichiometry --> helps figure out the quantities of products and reactants in a chemical equation --on the MCAT it is represented in units of grams, atomic mass units (amu) and moles --this will definitely appear on the MCAT --one proton or neutron has a mass about 1 amu; therefore, mass in amu represents the total number of protons and neutrons in the atom --biochemists call amu a dalton ex. on the periodic table, atomic weight of carbon is listed as 12.011 amu which is very close to 12 amu because almost 99% of carbon in nature is 12C --overall, amu=grams/mole --a mole can be thought of a bunch of atoms or molecules like 1 mole of CH4 --another way of understanding it is that is similar to the word dozen which is 12 of something or score which is 20 of something --Avogadro's number 6.022x10^23 amu is equal to 1 gram --referring back to mole, a mole is 6.022x10^23 of something (ex. of or equal to number of carbon atoms in 12 grams of 12C) --when dealing with multiple elements or compounds, use moles for units --to solve for moles (amount of an element or compound in a sample in grams)/(atomic or molecular weight) --so moles=(grams)/[(grams/mole)] --vice versa is amu=g/mol

Strong vs. Weak Acids and Bases

Strong Acids and Bases: --a strong acid has a weak hold on its hydrogen so it dissolves well in water --stronger acid means stronger than H2O --strong base is stronger than OH like NaOH --stronger means more dissociation in water **list of Strong Acids and Strong Bases to remember on Flashcards** --when 1M of aqueous solution of HCl, it means 1M of H and 1M of Cl --this goes for strong bases in the sense that the base reacts completely --Remember that percent dissociation of an acid decreases as the acidity of the solution increases --essentially, acids dissociate less or decreases in more concentrated solutions or with greater acid concentration --but acid strength increases with acid concentration ex. 100 acid molecules are in water and only 50 (or 400) dissociate meaning 50% (or 40%) dissociation and 50 (or 400) hydrogen ions produced --the greater amount of hydrogen ions produced in the same volume of water, the greater the acid strength Weak Acids and Bases: **weak acids and bases are on a flashcard to memorize** --consider deprotonation reaction of acetic acid CH3COOH⇌H + CH3COO

Thermodynamics: Physical Properties

Thermodynamics: study of energy transfer and change --use of energy transfer occurs when roasting a hot dog, pushing a lever and powering biological processes in the body --keep in mind that observable properties include temperature, pressure and volume --what correlates with atomic and molecular behavior are motion, force and bonding --to break a bond, energy is required while forming bonds releases energy --you can only figure out the average speed of the particles but it is impossible to know the exact speed and direction of each individual particle --the motion of individual molecules in a sample is random, unpredictable, and uninformative --but you can determine the sum total of motion of all the molecules Two Types of Properties to Describe Macroscopic State of a System: 1. extensive properties--> proportional to the size of the system. when two systems combined and the property doubles, it is extensive. remember, energy and number of moles are extensive property. so if thermal energy doubles, so does the number of moles meaning thermal energy/mole remains constant 2. Intensive properties--> independent of the size of the system. it is also when two identical systems are combined and the property is the same for when it's separated and when it's combined. if one extensive property is divided by another extensive property result in intensive property. temperature is an example of intensive property since two identical systems combined will not change the temperature. this also means that doubling thermal energy and -- Temperature: --represents the amount of molecular movement in a substance --when temperature increase, molecules in a solid vibrate faster --sum of the translational, rotational, and vibrational energies is called thermal energy --increase in thermal energy means increase in temperature --so when the temperature is at the lowest point, it means there is no molecular motion --equipartition theory states that in a normal system, each mode of motion will have the same average energy --it also states that energy of each mode will equal to 1/2kT where T is the temperature and k is Boltzmann's constant (1.38x10^-23 J*K^-1) --you can use the Boltzmann's constant (k) to solve for Ideal gas constant R by R=N.A x k --given the fact that there are three modes of kinetic energy, multiply 3 with 1/2k*T so KE=3/2k*T or KE=3/2R*T. know the formula for MCAT --greater the kinetic energy of gas molecules per mole means increased temperature --for the MCAT the unit that will be used are Celsius and Kelvin --keep in mind, at a pressure of 1 atm, the water freezes at 0C and boils at 100C --the lowest possible temperature is -273C which is the absolute zero and a volume of zero --for a graph with volume (liters) on the Y-axis and temperature (C) on the X-axis, it can help determine the ideal gas which is shown as a linear straight increasing slope in atmospheric pressure --when the slope lines for all different pressures intersect at the same point indicate the temperature is absolute zero --to calculate for Kelvin, simply add 273 to celsius --when in doubt, use Kelvin because celsius is a relative scale while kelvin is absolute --while it is wrong to say 12.5degrees C is half as hot as 25degree C (only celsius there's a degree sign), it is true to saw 149K is half as hot as 298K

Molecular Structure and Acid Strength

Three Aspects of Structure That Determines Acid: 1. the strength of the bond holding the hydrogen 2. polarity of the bond 3. stability of conjugated base (for the MCAT look at this primarily) --when looking at conjugate stability in mind, examine for acidic compounds that contain oxygen --electronegative oxygens draw electrons to one side of the hydrogen to increase polarity --the oxygen can also spread and share negative charge over a large area which makes the ion stable --so molecules with the most oxygens is the strongest acid ex. H2SO4 is stronger acid than H2SO3 --stability can be compared based on small size --basically, the negative charge is more concentrated causing it to be more unstable ex. HF is weaker of the hydrogen halide acid than HCl --another good example is CH4 vs. HCl, both have equal bond strength but HCl is more acidic due to bigger size --more acidic mean more polarity --another example is acetic acid (CH3COOH2) is a stronger acid than methanol (CH3OH) --it is because methanol has a simpler structure without resonance stabilization while acetic acid has resonance stabilization (when electron pairs move around chemical structure) Three Aspects of Structure That Determines Basic: --the strength of a base depends on the stability of the resulting species ex. NaOH is a strong base since it can readily dissociate and produce OH in aqueous solution --base strength is essentially the tendency to accept a proton since protonation of OH- stabilizes the negative charge to create a more stable H2O Ex. Link: https://www.chem.ucla.edu/~harding/IGOC/P/protonate.html --oxygen helps make acetic acids more stable because the negative charge is stabilized --ex. methyl amine is less basic than guanidine because the positive charge is formed on guanidine protonation --another way of looking at it is guanidine (HNCNH2) is a stronger base than methylamine (CH3NH2) --methylamine doesn't have a resonance stabilization since it doesn't have a double bond in this noncomplicated structure --but guanidine has a double bond and a charge from amine that can move around the chemical structure

Types of Radioactive Decay

Three Types of Radioactive Decay: 1. alpha decay--> loss of an alpha particle such as helium (4,2He or 4,2a) 2. beta decay or positron (0,-1e or 234,91PA from 90)--> is the breakdown of a neutron into creating proton and electron (n->p+e or n+e->p). since the neutron is destroyed, proton is created so the atomic number increases by one but the mass number stays the same. proton will then be eliminated by.... --> positron emission is when a proton becomes a neutron and positron is emitted. it is considered a beta decay. it is thought of as a electron with a positive charge. ex. is 0,1e. (p->n+e) --> electron capture can occur when electron is taken in as a proton is destroyed and is creating a neutron which will show up as 0,-1e (P+e->n) 3. gamma decay or production of gamma rays (0,0y)--> it is a high frequency photon or bundle of small particles typically energy like making up light. it has no mass or charge. this decay or ray emission often accompanies the other types of radioactive decay such as electron capture and positron --all these in its symbols can be used as a math equation on the MCAT --keep in mind that the sum of atomic # and sum of mass # on the left side of the equation equal the sum of the atomic # and sum of mass # on the right side Overall.. --alpha decay is loss of helium nucleus with a change in mass number of -4 and change in atomic or proton number of -2, making the element move two to the left on periodic table --beta decay is neutron becoming proton while electron is emitted or positron absorbed with no change in mass number but change in atomic or proton number of +1 making the element move one space to the right on PT --electron capture (a form of beta decay) is when proton becomes neutron (opposite of beta) while electron is absorbed with no change in mass number but a change in atomic or proton number of -1 causing it to move one space to the left on PT --position emission (a form of beta decay) is when proton become neutron (same as electron capture but opposite of beta) while positron is emitted with no charge of mass number but a change in atomic number of -1 causing element to move one space to the left on PT --gamma decay is when high energy gamma ray is emitted with no change in mass number, no change in atomic or proton number and no change in PT movement

Catalysis

catalyst --> is a substance that increases the rate reaction without being consumed or permanently altered --starting and ending concentrations of catalyst should be the same like the amount of enzyme in a pot --catalyst only affects the kinetics (energy of motion like collision) and not thermodynamics (equilibrium) of a reaction --this catalyst substance help increase the rate of both forward and reverse reactions --energy is less consumed (lower activation energy) and product selectivity is enhanced (by increasing steric factor; p from Arrhenius equation) --when activation energy is lowered, more collisions have sufficient kinetic energy to result in a reaction --this performance is shown on an energy vs. reaction coordinate diagram where uncatalyzed reaction has a slope much taller than a slope of catalyzed reaction --also on a graph of collisions (y-axis) vs. energy of collisions (x-axis), area under the slope closer to the middle/toward the y-axis represent catalyzed. uncatalyzed is area under the table further to the right of the graph or away from the middle and slope moves closer down to the x-axis --but, a catalyst cannot alter the equilibrium of a reaction Heterogenous vs. Homogenous Catalyst: --heterogenous when different phased substances (ex. liquid and gas) reacts with a solid --the particles stick to the surface of the solid due to intermolecular forces --the strength of the attraction between reactant and catalyst influence rate of catalysis --when the attraction is weak, catalyst has little effect on the reaction rate --when absorption is too strong, too much energy is required to remove the reactant so the catalyst doesn't facilitate the reaction --but, overall, more absorption allow greater reaction rate and reaction rate can be enhanced by increasing surface area of a catalyst --this is often done by grinding a solid into powder --homogenous is when catalyst is the same phase (typically gas or liquid) as reactants and products --aqueous acid and base solutions act as homogenous catalysts --homogenous catalyst can cause autocatalysis when product of the reaction acts as a catalyst for the reaction --increased catalyst concentration also increase rate reaction. when this happens, concentration of a catalyst will be found in rate law ex. rate=k.o[A}; when this original reaction is catalyzed by an acid it becomes rate=k.H[H][A] --but when the amount of catalyst is more than reactants and products, the rate is unchanged. in this case, it will not appear in rate law --example of catalyst in the human circulatory, respiratory and immune system is enzyme carbonic anhydrase CO2+H2O-><-HCO3+H

pH Scale and Equilibrium Constants

pH --> measure of hydrogen ion concentration --calculated by the formula pH=-log[H+] --bracket indicate concentration and the unit is measured in moles per liter --on a spectrum, value of 0 means very acidic such as HCl, HF, or HSO4- --value of 7 is neutral like water or H2CO3 --value of 14 is very basic so NaOH and these values are for 1M solutions and under constant temp 25C --each point on the range is a tenfold difference ex. pH of 2 means 10 times as many hyrogen ions as a solution with a pH of 3 --then pH 3 is 100 times more hydrogen ion as a solution with pH of 4 and so forth --pH uses the base 10 logarithm which can be used to solve problems like 10^x=3.16 (x=log3.16) --on the MCAT you don't have a calculator so you have to estimate Memorize Tips and Tricks of Logarithm: 1. 10^0 = 1 2. 10^1 = 10 3. log 10^-3 is -3 4. 10^2 = 100 or 10^4 is 10000 5. 10^-5 = 0.00001 6. log(10^2) = 2 ex. log(10^0) --> log (3.16) --> log(10^1) meaning log(1) --> log(3.16) --> log(10) measures X to around 0 --> 5 --> 1 6. log(AB)=log(A)+log(B) ex. log(10^2 x 10^3) = log(10^5)=5