CHEM 1, CHEM 2, CHEM 3

The Law of Mass Action

o Keq = [products]x/[reactants]y -the molarity values are the exponents... o Keq is written with every term raised to an exponent equal to its coefficient in the balanced equation (remember, however, that you do NOT do this when writing rate laws). Pure liquids (ℓ) and pure solids (s) are never included! Usually done in molarity, which moles/Liters How does each of the following affect equilibrium: addition of a catalyst- Does nothing to equilibirum increased temperature-exo rxn decrease Keq and endo rxn increase Keq, lowering the Ea-Lowering energy of activation impacts rate, NOT equilibrium stabilizing the transition state- same thing as EA addition of reactants/products- Does nothing to equilibirum, "temperature is the only thing that changes Keq."

Bond Energy

the energy stored in the bond. This is also the amount of energy that will be required to break the bond Don't confuse this; stable compounds such as N2 have the highest bond energies. Unstable compounds, such as ATP, have LOW bond energies. ATP- highly unstable= low energy bonds H2- Highly stable- high energy BONDS When something is said to be a "high energy" molecule that does NOT mean it has high bond energy. In fact, it means the very opposite. It is unstable and thus requires very little energy to dissociate the bond. ATP is high energy, thus highly unstable Bond energy is a measure of the strength of a chemical bond. The larger the bond energy, the stronger the bond HIGH ENERGY MOLECULE= LOW ENERGY BOND LOW ENERGY MOLECULE= HIGH ENERGY BOND

Hydration number

the number of water molecules an ion can bind via this solvation process, effectively removing them from the solvent and causing them to behave more like an extension of the solute the number of water molecules in a sphere of hydration

p-block

the p-block is the set of six columns starting with boron and ending with neon

pH Scale

the pH scale ranks solutions based not so much on the acids or bases themselves, but on how those acids or bases influence the equilibrium for the ionization of water.

Phase Diagram

o Lines on a phase diagram represent points where the two phases on either side of the line are in equilibrium. At the triple point all three phases are in equilibrium. Beyond the critical point, there is no distinction between liquid and gas and the phase is called a fluid.

Acid/Conjugate Acid and Base/Conjugate Base

the "conjugate base" of an acid is the acid minus its hydrogen (e.g., HCl = acid; Cl- = conjugate base). The "conjugate acid" of a base is the base plus a hydrogen (e.g., NH3 = base; NH4 + = conjugate acid). Which species you call the acid/base or the conjugate acid/base is arbitrary you could call HCl the acid and Cl- the conjugate base or call Cl the base and HCl the conjugate acid).

Salt of Weak Base

the "salt of a weak base" refers to the conjugate acid of that weak base combined with an anion to form a salt conjugate acid +Anion for weak bases NH3 = "weak base"; NH4+ = "conjugate acid"; NH4NO3 = "salt of a weak base" NO3- is the anion combining with the conjugate acid of NH4+ When the salts of weak acids or weak bases dissolve in water one of the ions will undergo hydrolysis to re-form the weak acid or the weak base: 1) NH4NO3 <-> NH4+ + NO3^2- 2) NH4+ + H2O <-> NH3 + H3O+

Pauli Exclusion Principle

the Pauli Exclusion Principles states that no two electrons can have the exact same four quantum numbers (i.e. occupy the exact same quantum state.) They can have up to three identical numbers, but then they must have opposite spins of +1/2 and -1/2.

d-block

the d-block is the entire set of transition metals in the middle of the table

normality

# of moles of equivalents/Liter solution. For example, a 1M solution of H2SO4 can be referred to as a "2 Normal" solution because it produces two moles of hydronium ions per Liter of solution. By the same token, a 2M solution of H3PO4 3- would be a "6 Normal" solution with respect to hydronium ions. This concept ignores the decreasing acidity of each proton. Some chemists discourage the use of this measure, but it has been used on the MCAT—albeit rarely. the concentration of a a solution given in equivalents of solute per liter of solution

Heating Curves

A graph of temperature (T) in Kelvin or Celsius vs. heat (q) in Joules. Occasionally, time is graphed on the x-axis instead of heat (if heat is added at a constant rate the temperature vs. heat graph and the temperature vs. time graph look approximately the same) the x-axis is usually a measure of the heat added/absorbed, but time can also be represented on the x-axis. The horizontal sections of the graph represent phase changes. The first flat section will represent the phase change between solid and liquid and the second will represent the phase change between liquid and gas. The graph remains flat during a phase change because changing the state of a substance requires energy. If heat is on the x-axis then the length of the first horizontal section represents the heat of fusion and the length of the second horizontal section represents the heat of vaporization. The slope of the lines between these horizontal sections represents the inverse (∆T/Q) of heat capacity (Q/∆T) for that particular phase of the substance. One should observe, therefore, that different phases of the same substance usually have different heat capacities—as indicated by the differing slopes of those sections of the following graph: THERE IS NO CHANGE IN TEMPERATURE DURING PHASE CHANGE, all the energy goes into breaking IM forces and none goes toward an increase in temperature

What two quantities are equal when a liquid boils?

A liquid boils when the vapor pressure of that liquid is equal to atmospheric pressure

Osmotic Pressure

A measure of the tendency of water to move from one solution to another across a semi-permeable membrane. Usually represented by the capital Greek letter pi, Π. It is the side that will receive the water via osmosis that has the higher osmotic pressure. In other words, more solute means more osmotic pressure. o Π = iMRT ; i = # of ions formed in solution, M is the solute molarity, R is the gas constant T is the absolute temperature.

∆G° = -nFE°

---n = number of moles of ELECTRONS transferred in a BALANCED redox reaction --- F= Faradays constant Faraday's Constant = the charge on one mole of electrons. ---F= ∆G°/(-nE°) ---Faraday's constant is the charge on one mole of electrons. ---One mole of electrons is 6.022 x 10^23 electrons. Each electron has a charge of 1.6 x 10^-19 C. ----Therefore, the charge on one mole of electrons is: (6 x 10^23 Moles)(1.6 x 10^-19 C) = 9.6 x 10^4 C/mol.

Alkali Metals

1A to the far left

Alkaline Earth Metals

2A just to the right of Alkali metals

Coordinate Covalent Bonds

: A covalent bond in which both electrons shared in the bond are donated by one atom. In most cases, more than one of these "donor" molecules surround and bind a single "recipient" molecule. The donor molecule must have a lone pair and the recipient molecule must have an empty orbital. ***If a molecule does not have a lone pair of electrons it CANNOT form coordinate covalent bonds with metals or other Lewis acids. The complex formed by the metal and the molecules forming coordinate covalent bonds with that metal, is called a "coordination complex." it typically happens when an atom donates it's electrons to the d the empy d orbital of another atom

Ionic Character

All bonds that are not between two atoms of the same element have some ionic character. It is basically a measure of the polarity of the bond. Ionic species such as NaCl have close to 100% ionic character. Covalent bonds between two non-metals of nearly identical electronegativity have close to zero ionic character. Ionic character is due to a difference in electronegativity between the two atoms in a bond. So, a C-C bond, for example, would have zero ionic character. Theoretically, the greatest possible ionic character would exist in francium fluoride.

Acid-Base Equilibria:

All equilibrium constants (Keq, Ka, Kb. Kw or Ksp) are written via the law of mass action, with pure liquids (l) and solids (s) OMITTED think of Ka or Kb just as you do Keq. A large Ka (or a small pKa) indicates that at equilibrium there are far more products than reactants. For an acid dissociation, this would mean a lot of dissociation (i.e., a lot of H+ formed) and thus a very strong acid. -aka large Ka or small pKa, ALOT OF DISSOCIATION Similarly, a large Kb (or a small pKb) indicates a very strong base (i.e., a lot of OH- formed—either from dissociation of a hydroxide base such as NaOH, or from deprotonating water). The acid-base equilibrium constant, Ka, is a constant (as the name suggests) for a given reaction at a given temperature, and therefore the negative log of that constant would also be a constant.

Strong Base

All strong acids and strong bases dissociate 100% in water (making them good electrolytes). There is obviously a continuum of strength, not a hard, fast line, but for the MCAT we will consider a species "strong" only if it is included in the following lists Group IA hydroxides (NaOH, KOH, etc.), NH2- , H-, Ca(OH)2, Sr(OH)2, Ba(OH)2, Na2O, CaO.

Strong Acids

All strong acids and strong bases dissociate 100% in water (making them good electrolytes). There is obviously a continuum of strength, not a hard, fast line, but for the MCAT we will consider a species "strong" only if it is included in the following lists HI, HBr, HCl, HNO3, HClO4, HClO3, H2SO4, H3O+

Base Dissociation

A- + H2O <-> OH- + HA Kb = [OH- ][HA]/[A- ] Ka*Kb = Kw = 10^-14 (at 25°C); because ([H+][A- ]/[HA])*([OH- ][HA]/[A- ]) = [H+][OH- ] = Kw Kw = Ka*Kb that Kb and Ka are inversely related, and therefore recognize that the smaller Kb represents the stronger acid (because Ka and acid strength are directly related

Raoult's Law

AS the solute is dissolved the vapor pressure of the solvent decreases. P(A) = X(A)P(A Vapor Pressure w/ a Non-Volatile Solute = (mole fraction of the pure solvent, X)*(Vp of the pure solvent, Vp°) Vp = XVp° Total Vapor Pressure w/ a Volatile Solute = (mole fraction of solvent* Vp° of the solvent) + (mole fraction of the solute* Vp° of the solute). Vp,total = Vp,solvent + Vp,solute = (Xsolvent Vp°solvent) + (Xsolute Vp°solute)

Double Displacement (Metathesis reaction)

A double displacement reaction, also known as a double replacement reaction or metathesis reaction, is a type of reaction that occurs when the cations and anions switch between two reactants to form new products.

Lewis

Acids accept a pair of electrons bases donate a pair of electrons AlCl3 and BF3 are two common examples of Lewis acids. The electrophiles in all organic chemistry reactions are acting as Lewis Acids. NH3, OH- and anything else with an electron pair to donate will act as a Lewis base.

Bronsted-Lowry

Acids donate protons (H+) bases accept protons (H+)

Arrhenius

Acids produce H+ ions in solution; bases produce OH- ions in solution.

Important Terminology Regarding Covalent Bonds:

BOnd length, bond energy, bond dissociation energy, heat of combustion

solution formation

For a solution to form, the intermolecular forces between the solute particles must first be broken, any intermolecular forces between the solvent particles must be broken to make room for the solute. New intermolecular forces are formed between the solute particles and the solvent particles: -If the new intermolecular forces formed are greater, more stronger/stable, than the sum of the intermolecular forces that had to be broken, the net energy is released and the solution is exothermic and has a negative Heat of Solution ΔHsolution < 0. Heat will be evolved -If the new IM forces are NOT more stable than the old ones, the solution has a positive ΔHsolution. The positive heat of solution means that energy must be added to the system to make the solute dissolve Entropy increases when a solution forms

C = q/∆T

C= heat capacity q= heat or energy ∆T= Change in temperature

Cyanide

CN-

Carbonate

CO3^2-

Use a rxn coordinate diagram to explain why the heat of combustion is greatest for the most unstable molecules

Carbon dioxide and water, compared to most other reactants or products, are very stable. Therefore, whenever you graph a combustion reaction you will expect the products to be very low on the y-axis (Energy). The heat of combustion, ∆Hcombustion, for the reaction will be equal to the difference in height between the products and reactants. So, the more unstable the starting products are, the higher they will be on the graph, and therefore the greater will be the difference in height between products and reactants.

Cations vs Anions

Cation- atom with fewer electrons than protons Anion- Any atom that has more electrons than protons Metals form Cations but non metals form anions Cations are smaller than their neutral counterpart and anions are larger than their neutral counterpart This size difference between anions, cations, and neutral atoms is due to the following: Cations are smaller because the relative charge in the electron cloud and nucleus increase by 1 unit, causing the electron cloud to suck in. Another reason on the differences in size is due to the fact that most cations form due to losing electrons to match electron configuration of nearest noble glass. This means they lose an entire shell and therefore volume. Anions are larger because those additional electrons take up additional space in the electron cloud, and repel one another, thus making electrons larger.

Standard Temperature and Pressure

For the MCAT, unless told otherwise, assume all gases are ideal and start out at STP --- At STP, the variables in the Ideal Gas Law are defined as follows: • P = 1 atm • V = 22.4 L • n = 1 mole • R = 0.0821 L*atm/mol*K or 8.31 J/mol*K • T = 273 K (0°C) STP is NOT Standard conditions: standard conditions is a set of agreed-upon conditions and are NOT interchangeable --- ex- STP is 0°C and temp in standard conditions is 25°C

Nitrite

Formula: NO2-

Fourth Quantum Number

Fourth Quantum Number: a.k.a. "ms" or "the electron spin quantum number" Gives the spin, which is either +½ or -½. Positive spin is represented by an up arrow in an electron configuration diagram and negative spin is represented by a down arrow. Electrons can "spin" two possible ways, thus two possible values So there is ms= +½, which is spin up and ms=-½, which is spin down.

Freezing Point Depression:

Freezing point of a liquid depressed when a non-volatile solute is added according to: ∆T = kfmi ; where kf is a new constant, different than kb above. --∆T = kbmi ; - kf is a constant - m is molality (NOT molarity) - i is the number of ions formed per molecule one can think of freezing point depression and boiling point elevation as being a function of not just moles of solute, but moles of solute particles

Gamma Emission

Gamma rays are usually emitted as a byproduct of the types of decay outlined above. Gamma decay does not change the number of nucleons!

Inorganic Nomenclature

General Ionic Compunds: Name the cation first, then the anion (i.e., calcium sulfate is CaSO4, not SO4Ca, and is not called "sulfate calcium") Transition Metals: When written in words, compounds that include transition elements must have a roman numeral showing the oxidation state of the metal (e.g., iron(II)sulfate vs. iron(III)sulfate) Monatomic Ions: Named by replacing the last syllable with "-ide." (e.g., sulfide ion, hydride ion, chloride ion, etc. Acids: Follow the "ate-ic - ite-ous" convention. If the ion name ends in "-ate," replace that ending with "-ic" as in: Nitrate Nitric Acid. If the ion name ends in "-ite," replace that ending with "-ous" as in: Nitrite Nitrous Acid. If the parent is a single ion rather than a polyatomic ion, replace the "ide" ending with "-ic" and add "Hydro-" as a prefix, as in: Iodide Hydroiodic Acid. Binary Compounds: Name the element furthest down and to the left on the periodic table first; use poly prefixes as necessary (e.g., Nitrogen Trioxide, Carbon Monoxide, Sulfur Dioxide, etc.). Some have common names such as ammonia and water.

Heat Capacity vs Specific Heat Capacity

Heat capacity is general and can change depending on the values we have. A 400 mL vessel of water vs a 100 mL vessel of water, the 400 mL will have a higher heat capacity than the 100 mL. Specific heat capacity is always specific for substances, example, 1.33 cal/gC for water will always be the same.

Ionization Energy

Ionization energy is the energy required to remove an electron from a neutral atom in its gaseous phase. Conceptually, ionization energy is the opposite of electronegativity. The lower this energy is, the more readily the atom becomes a cation. Generally, elements on the right side of the periodic table have a higher ionization energy because their valence shell is nearly filled. Elements on the left side of the periodic table have low ionization energies because of their willingness to lose electrons and become cations. Thus, ionization energy increases from left to right on the periodic table. Another factor that affects ionization energy is electron shielding. Electron shielding describes the ability of an atom's inner electrons to shield its positively-charged nucleus from its valence electrons. When moving to the right of a period, the number of electrons increases and the strength of shielding increases. As a result, it is easier for valence shell electrons to ionize, and thus the ionization energy decreases down a group.

Spectator Ions

Ions that may be dissolved into a solution but have no effect on the equilibrium. Addition of a common ion will cause precipitation. If a spectator ion is added no precipitation will result.

Isobaric vs Isothermal

Isobaric means constant pressure. Isothermal means no heat exchange (i.e., constant temperature).

Diffusion (Graham's Law)

It is the process by which gas molecules spread from areas of high concentration to areas of low concentration due to random motion imparted to them as a result of their kinetic energy and collisions with other molecules E1/E2=√MW2/√MW1

Kinetics

Kinetics is the study of reaction rate. how quickly the reaction proceeds. This is usually measured in terms of how fast the reactants disappear by tracking changes in the concentration of the reactants as a function of time (i.e., Molarity/second ; M/s) think of rate as depending on how fast the reactant molecules are moving (how much KE they have) and the relative height of the Energy of Activation "hill" that they must surmount in order to turn into products. The reactant molecules must also collide with the right orientation to one another. At any given time molecules in the mixture of reactants will have a variety of different energies. Some will have enough to react while others will not. Because temperature is a measure of the average KE of the molecules, increasing temperature will cause a greater fraction of the molecules to have sufficient energy to overcome the barrier and therefore more of them will react. if the reactants have more KE (higher temperature) they will be moving more quickly and collide more often, increasing the probability two reactants will strike one another with the correct orientation needed to react It is IMPERATIVE that students understand that the rate of a reaction is independent of its thermodynamic properties. It is trying to confuse you with the fact that solids and liquids are always left out of the formula for the equilibrium constant (Keq).

Ammonia

NH3

Ammonium

NH4+

Nitrate

NO3-

COlloids

NOT SOLUTIONS Colloids are solvents containing UNDISSOLVED solute particles that are too small to be separated by filtration Larger than solute particles in true solution Scatter light, while true solutions do not examples: Paint, dust

Hydroxide

OH-

Oxidation and Reduction

Oxidation- Loses Electrons, Loses H+ REduction- Gains electrons, gains H+

Phosphate

PO4^3-

Pressure Volume Graph

PV Work = P∆V (requires constant pressure, any change in volume tells you there is pv work) On a pressure vs. volume graph, the area under the curve is pv work.

Calculating Percent Mass:

Percent Mass = (mass of one element/total mass of the compound)(100%) Q20. What is the percent mass of carbon in glucose? What is the percent mass of hydrogen in water? The total MW of glucose is 180g. The weight of the six carbon atoms in glucose is 72g. Therefore, 72/180*100 = 40%. The total mass of water is 18g. The mass of the two hydrogen atoms is 2g. Therefore, 2/18*100 = 11%.

Phase Changes

Phase is distinguishing between a solid, liquid, and gas forms or states of a substance. When molecules are of the same phase: a) same state b) same chemical composition c) structurally homogeneous (same structure) example- carbon can be diamond or graphite, same state and chemical composition, but is structurally different.

Triple Point

Point on a phase diagram, shows only point where substance can exist in equilibrium as a solid, liquid, and a gas. precise temperature and pressure at which all three phases (i.e., states) exist simultaneously in equilibrium with each other

First Quantum Number

Principle Quantum Number n It gives the shell, valence e= are in outermost shell, and represents the relative energy of electrons in that shell Tells us the main energy level or the type of shell it is in As n increases, a higher energy level is associated it, example n=2 > n=1

Third Law of Thermodynamics

Pure crystalline substances at absolute zero have an entropy of zero. The crystal must be perfect, or else there will be some inherent disorder. It also must be at 0 K; otherwise there will be thermal motion within the crystal, which leads to disorder." the entropy of a perfect crystal approaches zero as its temperature approaches absolute zero.

Dalton's Law of Partial Pressure

Dalton's law states that the sum of partial pressures equals the total pressure If we add more of gas at P1 to an existing mixture of three gases, we increase the total pressure and the partial pressure of only gas 1. It has not effect on the partial pressures of the other gases. What does happen is when we add to P1 or any other parts, it doesn't decrease other partial pressures, but it does decrease the mole and mass fraction of other gases.

Calorimeters

Device used to calculate enthalpy change (∆H). We are assuming that q (which is what the calorimeter actually measures) is equal to ∆H. This is true at constant pressure. The assumption behind the science of calorimetry is that the energy gained or lost by the water is equal to the energy lost or gained by the object under study. So if an attempt is being made to determine the specific heat of fusion of ice using a coffee cup calorimeter, then the assumption is that the energy gained by the ice when melting is equal to the energy lost by the surrounding water. It is assumed that there is a heat exchange between the ice and the water in the cup and that no other objects are involved in the heat exchanged. This statement could be placed in equation form as Qice = - Qsurroundings = -Qcalorimeter which in essense is the following: q=∆H Coffee Cup Calorimeter: use q=mc∆T Bomb Calorimeter: Solve using: q = C∆T. This does NOT give enthalpy, but change in internal energy, ∆U or ∆E. Use heat capacity (big C) instead of specific heat capacity (little c). -

Radiation

Electromagnetic waves emitted from a hot body into the surrounding environment Charged particles being accelerated, they release electromagnetic acceleration. There is acceleration of charged particles and that releases electromagnetic radiation. The light you see from the fire is electromagnetic radiation that you can see. Light colors radiate and absorb less Dark colors radiate and absorb more A black body radiator- A thermal electromagnetic radiator that is within or surrounding a body in thermodynamic equilibrium with its environment. It has a specific spectrum and intensity that depends only on the body's temperature- theoretically perfect body that absorbs all energy incident upon it (or produced within it) and then emits 100% of this energy as electromagnetic radiation

Electron Configuration

Electron configurations are a list of quantum numbers and the number of electrons in each Energy level diagrams are the stair-step diagrams you drew in general chemistry with lines representing orbitals and up and down arrows representing electrons Orbitals are filled from low to high, always in order, so 1st to 2s, so on and so forth example- Carbon- 1s^2,2s^2,2p^2 hydrogen- 1s^1, Helium is 1s^2 Li- 1s^2, 2s^1 N=1s^2,2s^2,2p^3 Si=1s^2, 2s^2, 2p^6, 3s^2, 3p^2 NOble gas config example- Si=1s^2, 2s^2, 2p^6, 3s^2, 3p^2= [Ne] 3s^23p^2 Ni=1s^2,2s^2,2p^6,3s^2,3p^6, 4s^2, 3d^8: noble gas config= [Ar] 4s^2, 3d^8 -The 4s^2 is the valence electrons... The only remotely difficult MCAT question you'll face regarding electron configuration is to provide the configuration for cations and anions. For cations, move back one box in the periodic table for each electron missing. Ca^2+= [Ar] For anions, move forward one box for each extra electron.

Use the Fundamental Thermodynamic Relation to predict the answer to MCAT questions such as:

Q12. If ∆H is positive and entropy change is negative, what will the sign of ∆G be? Q13. If the change in entropy is positive, and enthalpy is negative, the reaction is: a) spontaneous, b) non-spontaneous, c) can be either spontaneous or non-spontaneous depending on temperature. Q14. If a reactant is dissolved in solution, causing the temperature of the reaction vessel to increase, the G for this reaction must be a) positive, b) negative, or c) cannot be determined.

Energy Levels

Energy levels represent the energies of the electrons in an atom. They are quantized! In other words, they look like stair steps, and do NOT look like a ramp. Electrons can be in energy level 1 or energy level 2, but never anywhere in between. The need more energy when they go higher in steps, when they then leave down the state, they show a color Ground state is most stable state of atom, excited state is any state other than the ground state of an atom. Electrons in atoms can only change to discrete energy levels

Galvanic Cells cont.

Reduction always happens at the cathode Oxidation always happens at the anode this ALWAYS happens for ALL electrochemical cells Cathode= + Anode= - This is only for galvanic cells, NOT electrolytic cells Cell Potential is ALWAYS positive for galvanic cells, NOT electrolytic cells A functioning Galvanic cell can be created using ANY two metals, regardless of their reduction potentials: this means that a current will always be produced between two species and the e- flow will occur from the lower reduction potential to the species with higher reduction potential

Farad

Farad= A unit of capacitance: it is a summary unit similar to newton, it is similar saying 1 Newton instead of saying 1 Kg*m/s²: we can say 1 farad instead of saying 1 C² * s²/m²*kg A farad is the amount of capacitance necessary to hold 1 C of charge on a capacitor with a potential difference of 1 Volt

Faraday vs. Farad

Faraday= obsolete unit of charge equal to thecharge on ONE mole of electrons, so Faraday's constant= 1 faraday Farad= A unit of capacitance: it is a summary unit similar to newton, it is similar saying 1 Newton instead of saying 1 Kg*m/s²: we can say 1 farad instead of saying 1 C² * s²/m²*kg A farad is the amount of capacitance necessary to hold 1 C of charge on a capacitor with a potential difference of 1 Volt

Examples of Nomeclature

Fe2O3= Iron (II) Oxide Ammonium Nitrate- NH4NH3 MgCl2- Magnesium Chloride Sodium Bicarbonate-NaHCO3 CaCO3= Calcium Carbonate Mercury (II) Sulfide= Hg2S Good practice sites: http://www.wbu.edu/academics/schools/math_and_science/chemistry/resources/inonomen/quiz.htm http://chem.libretexts.org/Core/Inorganic_Chemistry/Chemical_Compounds/Nomenclature_of_Inorganic_Compounds

Convection

Fluid movement caused by the hotter portions of a fluid rising and the cooler portions of a fluid sinking. Air currents and convection currents in water are examples. When temperature of wall or door from the air are in contact, convection occurs. When a material is hotter, heat rises, and the cold air goes down. cold air is more dense, falls to the bottom, hot air is less dense, thus rising.

Ideal Gas Law Assumptions

Focus on Following ideal conditions for the MCAT: 1) Gas molecules themselves are of negligible volume compared to the volume occupied by the gas. 2) All inter-molecular forces between gas molecules are negligible. Focus on the first two assumptions; they are responsible for most of the differences between what PV = nRT predicts, and how real gases actually behave. • To simplify things even further: THINK OF IDEAL GAS MOLECULES AS HAVING NO volume and NO inter molecular forces! Other Ideal Gas Assumptions: 3) All collisions between gas molecules are perfectly elastic 4) Gases are made up of a large number of molecules that are very far apart from one another 5) Pressure is due to collisions between gas molecules and the walls of the container 6) All molecular motion is random 7) All molecular motion follows Newton's laws of motion 8) The average kinetic energy (KE) of gas molecules is proportional to temperature --- types of gases don't matter, all gas in terms of ideal gas behavior are indistinguishable, ex- Cl2 same V has H2 gas --- # of moles of gas is the only measurement of molecules themselves we consider --- Gas molecules do not dissipate energy because of the assumption that all of their collisions— whether with each other or with the walls of the container—are perfectly elastic. As we recall from Physics 2, energy is conserved in a perfectly elastic collision.

Calculating pH for Strong Acids/Base

For Strong Acids/Bases: (e.g., pH of a 1 x 10-3M HCl solution) The pH or pOH = -log[strong acid or base] example= -log (1 X 10^-3)= pH=3

Heating curve of water

For a heating curve of water the phase change from solid to liquid should be shorter than the phase change from liquid to gas. This is because to change phases from solid to liquid only some of the intermolecular forces must be broken. Recall that hydrogen-bonding (the strongest type of intermolecular attraction) is prevalent in liquid water. In order to change phase from liquid to gas, all of these intermolecular hydrogen bonds must be completely broken (because no intermolecular forces exist between molecules in water vapor)

Collisions cause Reactions to Occur

For a reaction to occur: 1) The reactants must collide with enough energy to overcome the energy of activation 2) The reactants must be in the correct spatial orientation o Rate is measured as the change in molarity (M) of the reactants per second (M/s) How does the following affect reaction rate: Reactants- Increases rxn rate as long as reactants are in rate law Products- no effect Catalysts- Increase rate Energy of Activation- decreases reactions at constant temp. Energy of Transition State-decreases reactions at constant temp Energy of the reactants- Closer to Ea, thus increasing rxn rate Temperature-Increase KE, thus increasing rxn rate

Volatile

Liquids that evaporate quickly a term used to describe the relative tendency of a substance to form a vapor. How readily a substance vaporizes is primarily a function of its vapor pressure. Therefore, if one substance is said to be "more volatile" than another, this indicates that the former has a higher vapor pressure than the later at the same temperature

How to fill electron orbitals

Make sure students are familiar with the traditional order of progressing through the periodic table to fill orbitals. 1) between the s-block and d-block, where they need to know that the first d-block row is a 3d even though the orbital filled just prior to it was a 4s, 2) between the s-block, f-block, and d-block in rows 6 and 7; where they need to know that the lanthanide and actinide series are filled before proceeding with rows 6 and 7 respectively

Metals vs Non Metals

Metals: larger atoms, loosely held electrons, more likely to lose electrons form positive ions. Lustrous, ductile, malleable, conductors of heat and electricity. Ionic bonds with non metals Non-metals: smaller atoms with tightly held electrons. Nonmetals "like" to gain electrons and form negative ions. They have lower melting points than metals, and form covalent bonds with non-metals.

Permangate

MnO4-

Manganate

MnO4^2-

Conduction

Molecular collisions carry heat along a conduit, only with solids Recall that temperature is a reflection of the average kinetic energy of the molecules. High energy molecules collide with their neighbors, which in turn collide with their neighbors until eventually the energy is spread equally throughout KE is spread through higher temp. or Energy of molecules increase with higher Temp. Heat conduction is roughly analogous to current flow through a wire Conduction heat transfer occurs when there is two materials with different temperatures in contact with each other. Heat from high temp to low temp side. With

Moles of Oxygen Needed for COmbustion

Moles of Oxygen Needed for Combustion: You will occasionally be asked to predict the species that will require the most oxygen to combust. Here is a simple ranking system to make such predictions quickly: Add 1.0 for each carbon and subtract 0.5 for each oxygen. The higher the resulting number the more oxygen necessary for full combustion. This is NOT, however, the actual number of moles required—this is only a ranking system. The only way to determine the exact moles of oxygen required for a combustion reaction is to write out and balance the combustion equation.

Henry's Law

Most important: The solubility of a gas in a liquid is directly proportional to the partial pressure of that gas over that liquid. Primarily used to describe the solubility or partial vapor pressure of gases dissolved in liquids. There can be some confusion here, because Henry's Law is defined in multiple forms; Vapor Partial Pressure of solute = (mole fraction of solute)*(Henry's Law Constant) Vapor Partial Pressure of solute = (concentration of solute)*(Henry's Law Constant) Vapor Partial Pressure of solute = (concentration of solute)/(Henry's Law Constant) You must look up the constant that is specific to 1) the solute involved, and 2) the form of the equation you are using. Because of this complexity and potential for confusion, if Henry's Law shows up on the MCAT they will define it for you and give you the appropriate constant. We recommend you treat this section as background information only and focus on the following principle illustrated by Henry's Law above ↑↑↑

A pan of water is placed upon an electric heating element on a stove. Describe all types of heat exchange expected to occur in this scenario

Most students will assume the pan of water is cold. However, this is a good reminder that more careful thinking is usually rewarded on the MCAT. If the pot and water happened to be at the same temperature as the heating element then no heat exchange would occur. If the pan was hotter than the element (say the element wasn't even turned on yet), then heat flow would occur in the opposite direction to that most students will propose.

Electrical Potentials (E°)

Moving electrons can transfer energy E° show how much a species wants e-'s or wants to be REDUCED, aka gain e- These following potentials are given in volts and will ALWAYS BE PRESENTED IN WHAT IS CALLED A HALF REACTION ---Half Reaction The only half-rxns you will likely to are the following in the picture, that an aqueous metal is being reduced to form the associated solid metal. These are the most common ones that do not begin with metal cations: O₂, H₂O, H⁺

Avogadro's number

Avogadro's number of anything. Just as a dozen is defined as 12 of anything, a mole is 6.022 x 10^23 of anything. You can have a mole of atoms, molecules, cars, monkeys, whatever

Indicators Weak Acids

Indicators are weak acids that change color as they dissociate from HA into H+ and A- To set up a titration, you must know beforehand the approximate pH of your equivalence point; you then select an indicator that will change color at that approximate pH The dissociation of the indicator and the acid/base reaction we are analyzing run simultaneously in the same beaker but are otherwise unrelated. The amount of indicator is so small compared to titrant and analyte that we can assume it has no impact on pH.

The Common-Ion Effect:

The Common Ion Effect is a specific application of Le Chatelier's principle to solution chemistry. Consider the dissolution of Iron(III)Chloride in water: FeCl3(s) ↔ Fe3+(aq) + 3Cl- (aq). Suppose that enough solute is added to saturate the solution. If sodium nitrate is then added to this solution it would have no effect. However, if NaCl were added, the presence of extra chlorine ions from NaCl would—according to LeChatelier's Principle—drive the reaction to the left resulting in precipitation. In this example, chloride is considered a "common ion" and the precipitation as a result of its addition is what is referred to as the "Common Ion Effect." Other ions, such as sodium and nitrate—that do not shift the equilibrium—are considered "spectator ions."

The Reaction Quotient

The Equilibrium Constant can only be calculated at equilibrium. The reaction quotient Q is defined as the ratio of the concentration of the reacting species at any point of time other than the equilibrium stage. If you make the exact same calculation using concentration values taken at any point other than equilibrium the result is called the Reaction Quotient, Q. o If Q > K, the reaction will proceed to the left or reactants. o If Q < K, the reaction will proceed to the right or products. 1) Nature of reactants and products taking part in the reaction 2) Temperature 3) Stoichiometry of the equilibrium reaction

Heat Capacity

The amount of energy (Joules or Calories) a system must absorb to give a unit change in temperature (J/K or cal/˚C). THIS IS FOR A SYSTEM think of heat capacity as "the amount of energy we can add before the system increases by one temperature unit," So when something can hold more energy before Temperature change, it means that it has a higher heat capacity C = q/∆T C= heat capacity q= heat or energy ∆T= Change in temperature q>0 If heat is added to the system q< If heat leaves the system

ΔHvaporization

The amount of energy in Joules/mole required to go from liquid to gas OR the energy that must be removed to go from gas to liquid. Again, it describes both evaporation and condensation. the enthalpy change associated with the transition between liquid and gas. Solid -> Gas = Sublimation Gas -> Solid = Deposition

ΔHfusion

The amount of energy in Joules/mole required to go from solid to liquid or the energythat must be removed to go from liquid to solid. This describes the transition in both directions (i.e., melting and freezing). Solid to liquid= melting liquid to solid= freezing

Atomic Weight

The average mass, measured in amu, of all the isotopes of a given element as they occur naturally. Atomic weight (actually a mass; it cannot be a weight because it is not multiplied by gravity) is usually defined as the mass of one mole of any atom. however, just think of atomic weight/molar mass/molecular weight as the "g/mol" measurement given in the periodic table for individual elements, or in the case of molecular weight, the sum of those measurements for all of the atoms in a molecule. It is the number you will use to convert grams of any substance into moles

Oxidation State

The charge on an element after it gains or looses a certain number of electrons via bonding. It is the apparent charge an atom takes on while in a molecule The sum of oxidation states for all of the atoms in a molecule must equal the net charge on that molecule The oxidation states in the list is highest to lowest priority Always begin with the highest atom in the list and give it priority over the other ones, assigning the charge of the other atoms as needed to match the net charge on the molecule The oxidation state of monatomic ions is always equal to the charge on the ion

Half Life Problems

The half-life of a substance (t1/2) is the amount of time required for exactly one-half of the mass of that substance to disappear due to radioactive decay.

Q5. Beakers 1 and 2 contain 0.25 L of water and 0.5 L of water, respectively. How does the heat capacity of the water in Beaker 1 compare to that of the water in Beaker 2? How do the specific heat capacities compare?

The heat capacity of Beaker 2 will be greater than that of Beaker 1 because there is more water available to absorb heat in Beaker 2. However, the specific heat capacity of water in both beakers will be identical - specific heat capacity is an intensive property.

Alpha Decay

The loss of one He nucleus, which has a mass number of 4 and atomic number of 2 Mass accounts for protons

Q38. Why can you usually ignore the rate law for the uncatalyzed reaction?

The uncatalyzed reaction usually proceeds at a rate that is much slower than the catalyzed reaction. Therefore, the products from the reaction will be almost exclusively result from the catalyzed pathway. We can ignore the parallel uncatalyzed reaction because even though we know it is occurring simultaneously, its contribution to the progress of the reaction is negligible.

Lanthanides

The upper row in the f-block

Saturated Solution

a solution that contains the maximum amount of dissolved solute it can hold. For a saturated solution the ion product equals the Ksp.

Vapor Pressure

Vapor Pressure (Vp) is the partial pressure of the gaseous form of a liquid that exists over that liquid when the liquid and gas phases are in equilibrium. Vapor Pressure Elevation/Depression: 1)temperature- --- ↑ Temp,= ↑ Vp due to ↑ in KE, thus higher avg KE with ↑ Temp 2) non-volatile solute- ---↑ non-volatile= ↓Vp 3) Volatile Solute- --- ↑ V.S.= ↓ Vp: if Vp of V.S. < Vp of pure solvent ---↑ V.S.= ↑ Vp: if Vp of V.s. > Vp of pure solvent,

ΔHvaporization

When a liquid vaporizes, the liquid must absorb heat from it's surroundings to replace energy taken by the vaporizing molecule-s in order for the temperature to remain constant. This heat required to vaporize the liquid is called the enthalpy of vaporization. The enthalpy value associated with the phase change from liquid to gas. The reverse process (condensation) simply interchanges products and reactants and thus the sign is just changed.

How does the addition of a volatile solute affect vapor pressure?

When a volatile solute is added to a solvent it usually decreases vapor pressure for the same reason that a non-volatile solute decreases vapor pressure. As long as the vapor pressure of the solute is LESS THAN the vapor pressure of pure solvent, addition of the volatile solute will decrease vapor pressure. However, if a solute is added that has a vapor pressure greater than that of the pure solvent, then the vapor pressure of the solution will actually be higher than that of the pure solvent. This can be seen by simple examination of the formula for calculating the vapor pressure of a solution containing a volatile solute: Vp = (Xsolute*Vpsolute) + (Xsolvent*Vpsolvent).

Pressure-Volume (PV) Work

Work is energy transfer via a force (physics), or via a change in volume at constant pressure (chemistry). PV Work = P∆V (requires constant pressure, any change in volume tells you there is pv work) On a pressure vs. volume graph, the area under the curve is pv work. Q7. Which of the calorimeters described above allows for pv work? - Coffee calorimeter, because it utilizes constant pressure and utilizes a change in volume.

Periodic Table Trends

Size Matters, families are similar, Zeffective Size Matters refers to the trend that is depend on atomic size. Smaller atom's nuclei are closer to their valence electrons and are held more tightyl to positively charged nucleus. Greater force causes atoms to be more electronegative, having higher ionizatione nergy, greater electron affinity, and less metallic character than a larger atom. Larger atoms are better at stabilizing charges, don't form pi bonds and have d orbitals where they can house extra electrons. They won't form pi bonds because they are weak due to decrease in overlap of p orbitals Families are elements in the same column that have similar properties chemically and physically, like SiH4 is similar to CH4

Specific Heat Capacity

Specific Heat Capacity, however, describes energy absorption for one individual substance only and is defined per unit mass. Little "c" is used instead of big "C". The amount of heat needed to increase the temperature of one gram of a substance by one degree is the specific heat capacity Specific heat capacity is SPECIFIC FOR EACH SUBSTANCE! It doesn't change Heat capacity can change c = q/m∆T ; often re-written as: q = mc∆T Specific Heat of Water = 1.0 cal/g˚C or 4.18 J/g˚C

Entropy (∆S)

a measure of the randomness or disorder in a system. Reactions and other processes will be more likely to be spontaneous if they increase entropy. Entropy is measured by Joules/K As rxn proceeds forward, if randomness increases, energy is released and energy can do work If randomness decreases, energy is needed to increase/create order, thus that energy is unavailable to do work. positive ∆S = increased randomness, and thus more energy available to do work. -With increased randomness, the energyc an focus on doing work negative ∆S = decreased randomness, and thus less energy available to do work. -The energy is being used to create order, which requires energy, thus taking away energy to do work. Reactions at equilibrium are at maximum entropy.

Decomposition Reaction

a reaction in which a single compound breaks down to form two or more simpler substances

Precipitate

a solid produced during a chemical reaction in a solution a solid formed inside of a solution as the result of a chemical reaction, such as the common ion effect. Precipitates only form when the ion product exceeds the solubility product constant, Ksp. For example, given the dissolution of iron(III)chloride in water- [Equation: FeCl3(s) ↔ Fe3+(aq) + 3Cl- (aq)], if NaCl is added to the solution Le Chatelier's principle predicts that the reaction will shift to the left, reforming the solid.

Cell Potential

aka Cell EMF or E° cell The cell potential or E° cell is the SUM of E° potentials for two half rxns that make up an electrochemical cell Remember the following: 1) Half rxns ALWAYS come in pairs- one reduction half rxn + one oxidation half-rxn ---When one species is reduced, the other must be oxidized 2) Normally, reduction half rxns are given in tables. The oxidation half rxn is the REVERSE of the REDUCTION half-rxn --- E° for any oxidation halfrxn is simply the negative of E° for the associated reduction half rxn --- example- if a two species compared were -.32V vs -.5V, due to -.32V being greater, it is the reducing half rxn and -.5V is oxidation, thus its -.32V + .5V= .28V for the E° cell 3) You CANNOT add two E° values directly of a half-rxn table, all the reduction half rxn, thus you need one reduction and one oxidation: REVERSE the half rxn of the species with the LOWEST reduction potential and take the sum to get cell potential (E°cell) 4) DO NOT USE STOICHIOMETRY, one mole of Cu²⁺ has the same reduction potential (E° potential) as two moel-s of Cu²⁺ A strong oxidizing agent has a HIGH reduction potential, it is going another agent to be oxidized, and the oxidizing agent itself is gaining e-

Combination Reaction

also known as a synthesis reaction in chemistry is when two or more substances, or reactants, combine with each other to form a new product. The product will always be a compound.

Know how to convert Celsius to Kelvin

always use Kelvin in formulas, unless Celsius is specified.

Hydrate

an inorganic compound in which water molecules are permanently bound into the crystalline structure. The nomenclature of a hydrate is altered to reflect the presence of water molecules. For example, anhydrous cobalt(II)chloride contains no water, but cobalt(II)chloride hexahydrate [CoCl2∙6H2O] contains six water molecules complexed with each cobalt

Electron Orbitals

an orbital equates to a room and each room has two beds to be occupied by a maximum of two persons/electrons. There is only one room in an s subshell (studio apartment) and it can hold two electrons. There are three bedrooms in a p subshell and each bedroom can hold two electrons for a total of six. There are five bedrooms in a d subshell and each bedroom can hold two electrons for a total of ten. There are seven bedrooms in an f subshell and each bedroom can hold two electrons for a total of fourteen. Much like teenagers, electrons do NOT like to share rooms. Therefore, they will always fill empty orbitals first and only pair up inside the same orbital once it becomes necessary.

Aqueous

any solution for which water is the solvent.

Unsaturated Solution

any solution that contains less than its maximum amount of dissolved solute. For unsaturated solutions the Ksp is greater than the ion product. A super-saturated solution is a solution that contains more dissolved solute than predicted by the solubility product constant—in other words, the ion product exceeds the Ksp without a precipitate forming

Half-Equivalence Point

midpoint of the nearly horizontal section of the graph At this point, pH = pKa For example- [HA] = [A-] at the half-equivalence point. HA will continue to be deprotonated until at the equivalence point the solution contains 100% A- and 0% HA. This isn't true of SB and SA titrations- this is due to both SB and SA dissociating 100%, thus only having the Equivalence point and NO half-equivalence point The analyte will ALWAYS equal the titrant at equivalence points, but the moles of OH- vs H+ WONT always be the same, UNLESS it is for a SA with SB

molality

moles solute/Kg solvent Molarity (M) changes w/ temperature, but molality (m) does not.

molarity

moles solute/Liter solution Molarity (M) changes w/ temperature, but molality (m) does not.

mole fraction

moles solute/total moles solution (solute + solvent)

Second Law of Thermodynamics

o Heat cannot be changed completely into work in a cyclical process. o Entropy in an isolated system can never decrease- the disorder will never decrease -Heat will never flow spontaneously from colder object to a hotter object. example- when we have an ice cube on our hand, we don't feel the cold, but we feel heat loss from our hand because heat is being transferred into the ice cube.

Zeroth Law of Thermodynamics

o If object A is in thermal equilibrium with object B, and object C is also in thermal equilibrium withobject B, then objects A and C must be in thermal equilibrium with each other. For the MCAT, Just Remember This: Everything tends to move toward thermal equilibrium with everything else. Objects with higher temperatures will always equilibrate over time with their surroundings, including other objects with which they are in contact. Finally, if two objects are in thermal equilibrium, by definition they have the same temperature. NO NET HEAT IS TRANSFERED KE = 3/2kBT

Rates of Multi-Step Reactions:

o If there is a slow step, the slow step always determines the rate. o If the slow step is first, the rate law can be written as if it were the only step. o If the slow step is second (based on a few assumptions that are beyond the MCAT) the rate law is the rate law of the slow step—which will include an intermediate as one of the reactants.

∆G = ∆H - T∆S

enthalpy is basically the change in bond energy from reactants to products. If there were no change in randomness during the reaction, the amount of energy available to do work (ΔG) would be exactly equal to enthalpy (∆H). As described above, if randomness increases (positive ΔS), energy will be released and that energy (in addition to ΔH) will also be available to do work (creating a larger, more negative ΔG). if randomness decreases, energy will be "used" to create this order, decreasing the amount of energy available to do work The "T" term in the equation converts entropy into joules (J/K*K = J). You may recall that energy can also be used to increase temperature or to expand the volume (PV work), but neither occurs here because the system is both isothermal and isobaric.

Equivalence Point vs. End Point

equivalence point is where [titrant] = [analyte] -(that doesn't necessarily mean though that moles are equal to each other, especially with WB with SA or WA with SB The end point is simply the point when the indicator causes the color change. There is no causal relationship whatsoever between the solution reaching the equivalence point and the indicator changing color

First Order

ln[A] vs. time is linear with slope =-k A first order reaction depends on the concentration of only one reactant (a unimolecular reaction). Other reactants can be present, but each will be zero order. The rate law for a reaction that is first order with respect to a reactant A. It is only linear if it is the ONLY REACTANT or IF ONLY ONE REACTANT MATTERS. If it is non linear, it means it isn't first order

mass percent

mass solute/total mass of solution * 100

ppm

mass solute/total mass solution * 10⁶ (for ppb multiply by 10⁹) Parts per million (ppm) is NOT a measure of how many solute particles there are per 1 million total particles. Although that is how most students erroneously think of it. It is nothing more than mass percent multiplied by 10^4, or "mass fraction" multiplied by 10^6. The purpose of multiplying by 1 million is to make very, very small concentrations easier to work with. ppm = mg/Kg = mg/L (since 1 L of water has a mass of 1 Kg)

Acid Dissociation

HA + H2O <->H3O+ + A- (H3O+ is the same as H+) Ka = [H+][A-]/[HA]

Bicarbonate

HCO3-

Anyhydrous

a compound that can form complexes with water to differentiate molecules that do not contain water from those that do A compound with all water removed, especially water of hydration. For example, strongly heating copper(II) sulfate pentahydrate (CuSO. 5H2O) produces anhydrous copper(II) sulfate (CuSO4).

Actinides

actinides are the lower row in f- block

Buffers

A buffer solution contains a weak acid and weak base, often the conjugates of each other. In a buffer there is an equilibrium between a weak acid and its conjugate base, or between a weak base and its conjugate acid. The nearly horizontal area surrounding the half-equivalence point is called the "buffer region." Adding a relatively large amount of titrant at this point in the titration will have little effect on pH

Electron Capture

A proton is changed into a neutron via capture of an electron.

Positron Emission

A proton is changed into a neutron, with expulsion of a positron. We are doingP+N and P-1, we are reducing a number of protons. similar to electron capture

Reducing Agent

An atom or molecule that donates e- to another atom or molecule and is itself oxidized in the process ELECTRON DONATOR

Solution Chemistry

A solution is a homogenous mixture of two or more compounds in the same phase. (We usually think of all solutions as being in the liquid, or "aqueous" phase; however, a homogenous mixture of gases is also called a "solution".) Solvent vs SOlute: - Solute is the substance dissolved into solvent - solvent is more abundant than solute

Titration Curves: Weak Acid with Strong Base

As with the strong acid titration, this one will start at a pH below 7, but since the weak acid only partially dissociates, the pH will be higher than it is for a strong acid, or usually around 3 to 5. For WA w/ SB: pH > 7 As strong base is added, the pH will increase slowly through the buffer region and then go vertical at the equivalence point. The equivalence point won't cover as many pH units as it did for the strong acid titration and leading up to it and after it, the pH will more quickly rise than it did for the strong acid. The half way pH of the equivalence point will not be 7 as it is for a strong acid, it will be higher than 7. This is because the conjugate base of the weak acid is now present, creating a basic solution. After the equivalence point, the pH will slowly rise as more base is added.

Oxidizing Agent

Atom or molecule that accepts e- and is REDUCED in the process ELECTRON ACCEPTOR

What increases or decreases as you go across a period or down a group of the period table

Atomic size decreases going across the table or up any column. Fluorine is the smallest atom, except for hydrogen and helium (the noble gases are actually larger in size than the group 7A elements). From this we can intuit anything Electron Affinity: greatest for the smallest atom and least for the largest atom. Electronegativity: greatest for the smallest atom and least for the largest atom. Ionization Energy: very small for a very large atom and larger for a smaller atom Atomic Radius: Atomic size decreases going across the table or up any column Metallic Character: Metallic character will increase with the size of the atom do NOT want students to memorize these trends. ONLY to learn the patterns for changes in atomic radius and then use intuition to quickly determine the pattern for whatever characteristic they are evaluating.

Atomic Radius

Atomic size gradually decreases from left to right across a period of elements. This is because, within a period or family of elements, all electrons are added to the same shell. The effect of increasing proton number is greater than that of the increasing electron number; therefore, there is a greater nuclear attraction. This means that the nucleus attracts the electrons more strongly, pulling the atom's shell closer to the nucleus. The valence electrons are held closer towards the nucleus of the atom. As a result, the atomic radius decreases.

Boiling Point Elevation:

Boiling point of liquid is elevated when a non-volatile solute is added according to: ---∆T = kbmi ; - kb is a constant - m is molality (NOT molarity) - i is the number of ions formed per molecule (a.k.a., The Van't Hoff Factor; i.e., for NaCl i = 2; for CaCl2 i = 3).

Titration Curves: Strong Acid titrated with a Strong Base

A strong acid in the flask will result in the pH being low, around 1 to 2 depending on the [SA]. As strong base is added, the pH will stay low and slowly rise until the equivalence point is reached and then it will go straight vertical for around 6 pH units. The middle of the equivalence region will be pH 7. After the equivalence point, the plot will slowly go to higher pH as more strong base is added

Super-saturated Solution

solutions usually form only when a solution is held at a higher temperature during dissolution (at which Ksp would be larger) and then slowly cooled to a temperature at which Ksp is smaller.

Calorie and other values

1 kcal=1 kg water x 1'C 4.184 J/1 cal 1 Kg/1L 1 kcal/kg water x 1'C 1Kg/L = density of water Convert liters into grams using 1 Kg/L

Amphoteric

substances can act as either an acid or a base (e.g., H2O).

Super critical Fluid

super-critical fluid cannot be compressed back into the liquid phase by increasing pressure, nor can it be turned into a gas by increasing temperature

Specific Heat of Water

1.0 cal/g˚C or 4.18 J/g˚C ALSO REMEMBER ROOM TEMPERATURE IS (25°C).

s-block

the s-block is the first two columns

Second Order

1/[A] vs. time is linear with slope = k A second order reaction depends on the concentrations of one second order reactant, or two first order reactants.

Nernst Equation

E= E° - (.06/n) * log [lower]/[higher] n= Moles of e- transferred example- Fe³⁺ (aq) → Fe(s) = 3 moles of e- being transferred, or if it is Ag⁺ (aq)→(Ag(s), then 1 mole of e- is transferred. Remember that E°Cell for a concentration cell, will ALWAYS equal 0, because you are using the same species for both the anode and cathode, for the reduction and oxidation half equation

Calculating ΔH from a heating curve:

ΔHfusion = The change in q (x-axis) during the phase change from solid to liquid. ΔHvaporization = The change in q (x-axis) during the phase change from liquid to gas.

Bond Length

distance between the nuclei of the atoms forming the bond the shorter the bondlength, the higher the bond energy, more stability, thus more energy

Sulfate

SO4^2-

Second Quantum Number

"ℓ" or "the azimuthal quantum number" or "the angular momentum quantum number" ℓ n-1= # of subshells Gives the subshell or orbital; has values of 0, 1, 2 or 3, and from this we know the shape: 0 = s ; 1 = p ; 2 = d ; 3 = f The shape of the orbital, ℓ can equal 0, 1, 2, -1, so when n=1, ℓ=0, this refers to s orbital that is shaped as a sphere n=2, ℓ=0,1 thus we have 2 allowed values, so when ℓ is equal to 0, we get a sphere, if ℓ=1, then we get a p orbital (dumbell)

Rate Order Graphs

These graphs will only be linear when the reaction has only a single reactant, OR when it is part of a multiple-reactant reaction where the rate is independent of ALL the other reactants (e.g., the other reactant is zero order, or is in excess) Zero Order, First Order, Second Order. Something is ONLY LINEAR when there is ONE reactant, and it's the only one that has an effect.

Bond Dissociation Energy

it is the same as bond energy, the amount of energy required to break or "dissociate" the bond.

Q26. How many equivalents of base can be neutralized by one equivalent of H2SO4?

Two equivalents of base can be neutralized by one equivalent of H2SO4 because each sulfuric acid produces two equivalents of hydrogen ions in solution. Look to the H+ ratio to the base ratio, so 2:2

pH = pKa + log[A-]/[HA]

or pH = pKa - log[HA]/[A-] At the half-equivalence point the concentrations of HA and Aare equal. Therefore, the ratio of [A-]/[HA] must be one. When we plug this into the H-H equation we get: pH = pKa + log(1). The log of one is zero, so this term falls out, demonstrating that pH = pKa at the half-equivalence point.

pH = -log[H+]

pH of pure H2O at 25°C = 7.0, and the [H+] = [OH-]; pH > 7 = basic, and the [H+] < [OH-]; pH < 7 = acidic, and the [H+] > [OH-]; pH = 7 is defined as "neutral" and the [H+] = [OH-]

pOH = -log[OH-]

pH of pure H2O at 25°C = 7.0, and the [H+] = [OH-]; pH > 7 = basic, and the [H+] < [OH-]; pH < 7 = acidic, and the [H+] > [OH-]; pH = 7 is defined as "neutral" and the [H+] = [OH-]

∆E = q + w

E= Change in Temp in a system or the total change in internal energy of a system q= THe heat exchanged between a system and it's surroundings w=work done by or on the system

Ionization of Water:

(H3O+ is the same as H+) Kw = [H3O+][OH-] = 10^-14 pKw = pH + pOH = 14 pKa + pKb = 14 If we are at 25°C, we know that Kw will be exactly 10-14 and the concentrations of H+ ions and OH- ions will both be 10^-7M.

The Solubility Product Constant (Ksp)

(Ksp) 1) Leave out pure liquids and pure solids (this will make all Ksp equations only have a numerator - if you have something in the denominator of a Ksp equation, you've made a mistake). 2) Temperature is the only thing that changes Ksp (the MCAT does not include activity coefficients). 3) Ksp can only be observed in a saturated solution. This is because saturation is the point at which the dissolution reaction has reached equilibrium. In other words, it's just like all other equilibrium constants—you cannot measure them anywhere other than at equilibrium.

Calculating pH for Weak Acids

(e.g., pH of a 1 x 10-4M CH3COOH solution) 1) Write out the equilibrium equation (HA <-> H+ + A-). 2) Use x to represent the concentration of each of the two products (or 2x, 3x etc. depending on the coefficients in the balanced equation).- AKA BALANCE OUT THE EQUATION 3) Use "[HA] - x" for the concentration of the original acid. 4) Solve for x from the resulting equation: Ka = (x)(x)/[HA - x]. 5) If this results in a quadratic equation, assume that x is much smaller than [HA] (in step #3 above) and omit it. 6) Use -log[H+] to solve for the pH.

Bonding and Anti-Bonding Orbitals:

1) Anti-bonding orbitals are higher in energy than bonding orbitals. 2) Bonding orbitals contain electrons that are "in phase" and are said to be "attractive"; anti-bonding orbitals contain "out of phase" electrons that are said to be "repulsive." 3) Know what drawings of bonding and anti -bonding orbitals look like.

Step-by-Step Instructions for Balancing a Reaction:

1) Balance the number of carbons 2) Balance the number of hydrogens 3) Balance the number of oxygens 4) Balance the number of any remaining elements 5) If necessary, use fractions. For example, if you have seven oxygens on one side of the reaction and one O2 on the other side, put 7/2 in front of the O2. 6) Multiply all of the species on both sides of the reaction by the denominator of any fractions. 7) Double check your work by counting the number of atoms of each element found on each side of the reaction. One of the most common errors is failure to multiply by a coefficient. For example, you might accidentally count 2CO2 as 2 oxygens when there are actually 4 oxygens present. THE MCAT WILL GO YOU UNBALANCED REACTIONS..

Deriving a formula from percent mass

1) Change the percent mass for each element into grams (i.e., 15% = 15g), always do it out of 100g, its the easiest 2) Convert the grams of each element into moles by dividing by molar mass. 3) Look at the element with the lowest number of moles. Calculate approximately how many times it will divide into each of the other molar amounts for each of the other elements—this number will be the subscript for each element in the empirical formula. If the subscripts are not at their lowest common denominator, reduce to get the empirical formula. An empirical formula is all you can get from percent mass alone. To get the molecular formula, you must be given the MW of the unknown compound. If you have the molecular weight of the actual compound, simply divide that MW by the MW of the empirical formula. You should get a whole number. Multiply each subscript by that number to get the molecular formula.

To calculate the "order" of each reactant using experimental data:

1) Find two trials where the [reactant] in question changed, but all other parameters did NOT (i.e., the concentrations of the other reactants, temperature, pressure, etc., all remained constant). 2) Note the factor by which the reactant concentration changed. 3) Note the factor by which the rate changed across those same two trials. 4) Solve for Y in the following equation: XY = Z ; where X = the factor by which the [reactant] changed, Z = the factor by which the rate changed, and Y = the order of the reactant. Recall that any number raised to the zero power is equal to one.

Recognizing Buffer Problems:

1) Watch for equimolar amounts. -The maximum buffering strength occurs when the [HA] is equal to the [A- ]. This is the ratio one would start with if making a buffer in the lab. Therefore, be on the lookout for equimolar amounts of a weak acid and its conjugate base, or a weak base and its conjugate acid. 2) Watch for conjugates. -To be a buffer, the two equimolar substances are often conjugates of each other, such as: NH3 and NH4, CH3COO- and CH3COOH, or HCO3 - and CO3 2-. 3) Watch for WEAK acids or bases. - The equimolar pair must be a weak base or a weak acid and its conjugate. -Strong acid or strong base conjugate pairs do NOT form buffers. 4) Watch for resistance to pH change. -Any time an acid or base is added to a solution and the pH does not change "very much," or "changes slightly," this should be a dead giveaway that the solution is a buffer. -Anytime the chart shows a near horizontal line 5) Watch for the half-equivalence point. -Remember that only solutions of weak conjugate acid/base pairs have a buffer region, and therefore they are the only solutions that have a half-equivalence point. 6) Watch for pH = pKa. - Many students memorize this principle, but fail to recognize that what it is really saying is that pH = pKa at the midpoint of the buffer region. This is another unmistakable clue that you are dealing with a buffer. -THIS IS AT THE HALF-EQUIVALENCE POINT 7) Watch for the ratio of [HA]/[A- ] or [A- ]/[HA]. -One particular problem on the CBT practice exams seems to stump the majority of students. -The question stem asks about the ratio of an acid to its conjugate base. Those who recognize it as a buffer problem usually answer it correctly. Those who do not guess. -At the half-equivalence point the concentrations of HA and A are equal. Therefore, the ratio of[A-]/[HA] must be one. When we plug this into the H-H equation we get: pH = pKa + log(1). The log of one is zero, so this term falls out, demonstrating that pH = pKa at the half equivalence point.

Entropy increases with increasing:

1) number of items/particles/etc. Caveat: The number of moles of gas trumps the number of moles of species in any other phase. Thus, even if a reaction turns two moles of reactants into one mole of product, if that one mole of product is a gas, and the reactants are not, entropy has increased; and ∆S will therefore be positive. So anytime something becomes a gas, ∆S has increased. 2) volume, more space for molecules to move 3) temperature or increase KE, 4) disorder (e.g., S is greater for an amorphous material than for a crystal) 5) complexity (e.g., S is greater for C2H6 than for CH4) -With more moles, more complexity, there is more disorder, thus higher ∆S

How is vapor pressure affected by temperature?

1)temperature- --- ↑ Temp,= ↑ Vp due to ↑ in KE, thus higher avg KE in molecules with ↑ Temp

Hydrogen Half Cell

2H⁺ + 2e₋ → H₂ E° = 0.00 Volts E° values assigned to each half-rxn represent the relative reduction potential, aka the potential to gain e-, of that species compared to the E° of two H ions to gain 2 e- to form H gas This standard, the Hydrogen half-cell, is the standard which ALL other half rxns are compared, and it's E° is defined as E°= 0.00 V. Always compare half rxns to E°= 0.00 V. --- A species with + E° is more likely to gain e-, aka be reduced, than hydrogen ions --- A species with negative E° is less likely to gain e- than Hydrogen ions. It is all about what is compared to: a - reduction potential can be reduced as long as long it has a greater reduction potential than the species it is compared with: ex- -1.5v vs -1.8v, species -1.5v is reduced and species -1.8V is oxidized, so thus you do -1.5 + 1.8 and you get .3V, showing the cell potential, which is positive in this situation, would proceed spontaneously in a galvanic cell. FOr the MCAT, remember cations Cu⁺, Fe⁺,etc get reduced to form solid metals Cu (s), Fe(s), etc and solid metals get oxidized to form cations, but solid metals are NOT reduced

Catalysts:

A catalyst is any substance that increases reaction rate without itself being consumed in the process. Rate Laws for Catalyzed Reactions: Technically, the rate law is the sum of the rate law for the uncatalyzed reaction and the rate law for the catalyzed reaction. This fact, however, can usually be ignored, and you can assume that the rate law for the reaction is exactly equal to the rate law for the catalyzed reaction alone. Under such an assumption, write the rate law in the same way as normal, with the concentration of the catalyst added in as a reactant. The rate constant, k, is sometimes replaced with kcat. What do catalysts change?-They don't change Ea, but provide an alternate route that has a lower Ea What do they not change? -They do NOT change the equilibrium, Keq, enthalpy change, entropy change, Gibbs free energy, or any other thermodynamic properties.

A certain mixture has a large negative heat of solution. Describe the relative strength of a) the intermolecular forces between solvent molecules, b) the intermolecular forces between solute molecules and c) the intermolecular forces between solute and solvent molecules. Would you expect such a solution to have a higher or lower vapor pressure compared to a mixture with a positive heat of solution?

A negative heat of solution tells us that the dissolution releases heat. In order for this to occur, the solvent-solute bonds must be relatively stronger than the solvent-solvent and solute-solute bonds that had to be broken in order to dissolve the solute into the solvent. We would expect such a solution to have a lower vapor pressure than a solution with a positive heat of solution because—as stated at the outset—the negative heat of solution indicates strong solvent-solute interactions. It is these very intermolecular forces that must be overcome in order for solvent molecules to escape into the vapor phase. For a solution with a positive heat of solution, these attractions are relatively weaker, and therefore (at the same temperature) more of the molecules should have enough energy to enter the vapor phase.

Beta Decay

A neutron is changed into a proton with the ejection of an electron. The neutron is changed to a proton to help keep it at the correct atomic mass number. THat is why the neutron converts to a proton

Example of a Coffee Cup Calorimeter

A physics class has been assigned the task of determining an experimental value for the heat of fusion of ice. Anna Litical and Noah Formula dry and mass out 25.8-gram of ice and place it into a coffee cup with 100.0 g of water at 35.4°C. They place a lid on the coffee cup and insert a thermometer. After several minutes, the ice has completely melted and the water temperature has lowered to 18.1°C. What is their experimental value for the specific heat of fusion of ice? The basis for the solution to this problem is the recognition that the quantity of energy lost by the water when cooling is equal to the quantity of energy required to melt the ice. In equation form, this could be stated as Qice = -Qcalorimeter (The negative sign indicates that the ice is gaining energy and the water in the calorimeter is losing energy.) Here the calorimeter (as in the Qcalorimeter term) is considered to be the water in the coffee cup. Since the mass of this water and its temperature change are known, the value of Qcalorimeter can be determined. Qcalorimeter = m•C•ΔT Qcalorimeter = (100.0 g)•(4.18 J/g/°C)•(18.1°C - 35.4°C) Qcalorimeter = -7231.4 J The negative sign indicates that the water lost energy. The assumption is that this energy lost by the water is equal to the quantity of energy gained by the ice. So Qice = +7231.4 J. (The positive sign indicates an energy gain.) This value can be used with the equation from the previous page to determine the heat of fusion of the ice. Qice = mice•ΔHfusion-ice +7231.4 J = (25.8 g)•ΔHfusion-ice ΔHfusion-ice = (+7231.4 J)/(25.8 g) ΔHfusion-ice = 280.28 J/g ΔHfusion-ice = 2.80x102 J/g (rounded to two significant figures)

Galvanic Cells

Also known as Voltaic Cells Galvanic cells convert chemical energy into electrical energy. A current can be generated by using the reduction potentials (E° potential) between two metals, and generate a current along a wire that connects two metal electrodes submerged in solutions that contain metal ions. Why a salt bridge is necessary: ---In the cell above notice that over time there will be a buildup of negative charge in the copper vessel due to continual loss of copper cations, and a buildup of positive charge in the zinc vessel due to the continual production of zinc cations. This polarity resists the flow of electrons and would eventually shut down the cell if a salt bridge were not present. Within the salt bridge sodium ions can flow toward the copper vessel and nitrate ions can flow toward the zinc vessel, neutralizing the buildup of charge and allowing electron flow to continue. The metal cations themselves, as well as any other ions in the solutions, can also flow through the salt bridge. In an electrical sense, the salt bridge connects the circuit, allowing continual flow of electrons from electrode to electrode and then back through the salt bridge via ion diffusion.

The Ion Product

Also referred to as the "Solubility Product." The ion product has the same relationship to Ksp as Q does to Keq. Plug in the values for the actual concentrations of each species at some point other than equilibrium (i.e., for an unsaturated or supersaturated solution). If the product is greater than Ksp, you know a precipitate will form. If it is less than or equal to Ksp, then you know that no precipitate will form. If the ion product happens to be exactly equal to Ksp, then the solution must be exactly saturated (i.e., at equilibrium).

Energy Levels & Photon-Light Emission

Because energy levels are quantized, you cannot cause an electron to move up one energy level unless you add an amount of energy equal to the difference in energy between the current energy level and the higher energy level. If an electron is struck by a photon with an energy that is lower than the difference in energy between two energy levels in that atom the photon will pass through the atom without being absorbed. If an electron drops to a lower energy level, energy is released as a photon (i.e., as electromagnetic radiation). The energy released will be EXACTLY equal to the difference between the two energy levels. IN ORDER FOR THE ELECTRON TO BE FREED FROM THE NUCLEUS, IT NEEDS TO BE HIT WITH ENOUGH ENERGY THAT IS NOT ONLY EQUAL TO THE ELECTRON ENERGY LEVEL, BUT MUST BE IN EXCESS FOR TEH ELECTRON TO BE FREED. IT'S ALL ABOUT USING ENOUGH ENERGY FOR THE DIFFERENCE BETWEEN 2 ENERGY LEVELS, AND WHEN IT DOES HAPPEN, A PHOTON IS SHOT OUT WITH ENERGY REPRESENTING THAT DIFFERENCE.

The Work Function in Energy Levels

Bombarding certain metals with energy can cause the ejection of an electron from their outermost shell (i.e., valence electron). The amount of energy required to do this is called the "work function," and is usually given the variable φ. This may sound similar to "Ionization Energy." However, they are NOT the same. Ionization energies are measured for lone atoms in a gaseous state. The work function refers specifically to valence electrons being ejected from the surface of a solid metal. If the energy added is less than the work function, the electron won't be ejected. If it is greater than the work function, the excess energy will be transferred into the kinetic energy of the ejected electron. KE = E - φ ; where E is the amount of energy added and KE is the kinetic energy of the ejected electron. Because energy is usually added via bombardment with photons, E can be replaced with hf, the formula for the energy of a photon. E = hf ; where E = the energy of a photon, h = Planck's Constant (which is always given) and f = frequency.

Other Derivations of the Ideal Gas Law:

Boyle's Law: P1V1 = P2V2 (assumes constant temperature) Charles' Law: V1/T1 = V2/T2 (assumes constant pressure) Note: We find the two laws above to be of limited value for the MCAT because the relationships they demonstrate can be intuited from either the Ideal Gas Law or the Combined Gas Law.

Hypochlorite

ClO-

Chlorite

ClO2-

Chlorate

ClO3-

Perchlorate

ClO42-

Reaction Types:

Combination Decomposition Single Displacement Double Displacement (a.k.a. "metathesis reaction")

Good vs. Poor Electrolytes

Covalent compounds that dissociate 100% in water, such as strong acids and strong bases, make good electrolytes. Strong Acids, strong bases Other covalent compounds are usually poor electrolytes. Ionic compounds that are soluble in water always make good electrolytes Salts

Covalent vs. Ionic:

Covalent: formed between two non-metals and involve sharing of electrons within the bond. This sharing need not be equal, and is in fact usually not due to differences in electronegativity. ex- HCl, CO2 Ionic: Ionic bonds are usually formed a between a metal and a non-metal and are due to an electrostatic attraction ex- NaCl, cation + anion, solid at room tempreature They can be conceptualized in two ways. First, you can visualize the two species as previously formed ions. For example, Na+ and Cl-. It is fairly obvious that these two species will be strongly attracted to one another by an electrostatic force. Alternatively, you can also visualize it as if the two atoms came together in their ground states (not as ions) and the more electronegative atom (Clin this case) pulled one electron completely away from sodium. This would result in essentially the same result, a sodium cation and a chloride anion

Titrations

Drop by drop mixing of an acid and a base with an indicator Titrant vs Anylate One "equivalent" = the amount of acid or base necessary to produce or consume one mole of [H+] ions. Pay special attention to where the titration curve starts. Strong acids titrated with anything (strong or weak base) should start low on the y-axis Strong bases titrated with anything should start high on the y-axis. The end of the titration curve should correlate with the pH of the titrant. For example, if you're titrating with a strong base, near the end of the titration the curve should flatten out at a point high on the y-axis. If titrating with a weak base, however, the curve should end much lower due to the base not being as basic as the strong base

E=hf

E- Energy of a photon h= Plank's constant f=frequency v = f (lambda), f=v/lambda, which you can then plug into the energy equation for E=hv/lambda

E1/E2=√MW2/√MW1

E1 and E2 can represent either the effusion rate or the diffusion rate of gases 1 and 2 respectively RATE OF EFFUSION or DIFFUSION is INVERSELY proportional to the molecular weight of gas --- The lighter the gas, the faster the rate is --- The heavier the gas, the slower the rate is

Electronegativity

Electronegativity can be understood as a chemical property describing an atom's ability to attract and bind with electrons From left to right across a period of elements, electronegativity increases. If the valence shell of an atom is less than half full, it requires less energy to lose an electron than to gain one. Conversely, if the valence shell is more than half full, it is easier to pull an electron into the valence shell than to donate one. Electronegativity measures an atom's tendency to attract and form bonds with electrons. This property exists due to the electronic configuration of atoms. . Because elements on the left side of the periodic table have less than a half-full valence shell, the energy required to gain electrons is significantly higher compared with the energy required to lose electrons. As a result, the elements on the left side of the periodic table generally lose electrons when forming bonds. Conversely, elements on the right side of the periodic table are more energy-efficient in gaining electrons to create a complete valence shell of 8 electrons. The nature of electronegativity is effectively described thus: the more inclined an atom is to gain electrons, the more likely that atom will pull electrons toward itself.

Empirical vs Molecular Formula

Empirical formulas represent the lowest possible number of moles of each element that can be present in a compound while still maintaining the same mole-to-mole ratio between the elements. A molecular compound is the actual number of moles of each element found in a specific compound. For example, CH2O is the empirical formula for glucose, and C6H12O6 is the molecular formula for glucose. However, CH2O is also the empirical formula for all other carbohydrates. The subscripts for a molecular formula and its empirical formula will always differ by a factor of some whole integer. The two formulas can be the same. For example, the empirical formula for water is also the molecular formula.

First Law of Thermodynamics

Energy neither be created nor destroyed IMPORTANT NOTE: By convention, work done on the system is positive, work done by the system is negative (chemistry definition); o Two Common Ways to Define the First Law of Thermodynamics: 1) The total energy of an isolated system is always constant-An isolated system is a system for which neither mass nor energy can be exchanged with the surroundings 2) The energy change in a closed system is equal to the heat absorbed by that system plus any work done on that system by its surroundings.- A closed system is a system that can exchange energy with its surroundings but not mass. Definitions1 and or 2 are essentially saying the same thing: in definition 2, the surroundings and the closed system are considered an isolated system. Therefore, heat or work can be transferred back and forth between parts of the system and the total energy of the entire isolated system would not change. To further illustrate, let's say that 10J of heat were transferred to the system and 10J of work were also done on the system by the surroundings. -Any work or heat that goes into or out of a system changes the internal energy. However, since energy is never created nor destroyed (thus, the first law of thermodynamics), the change in internal energy always equals zero. If energy is lost by the system, then it is absorbed by the surroundings. If energy is absorbed into a system, then that energy was released by the surroundings: ∆E = q + w

Enthalpy ΔH

Enthalpy = the energy contained within chemical bonds we can calculate ∆H for a reaction (i.e., the change in enthalpy) by finding the difference in total bond energy between the products and the reactants Enthalpy is a state function which depends entirely on the state functions T, P, U. U is internal energy, T is temperature, P is pressure. If temperature and pressure remain constant, enthalpy is given in this state: ΔH=ΔU+PΔV MUST BE DONE AT A CONSTANT PRESSURE The units of Enthalpy is done in Joules Standard State: A set of specific conditions chosen as the reference point for measuring and reporting enthalpy, entropy, and Gibbs free energy Elements in their standard state have ∆Hformation° = zero. -This is because elements in their standard state are used to define the enthalpy scale and thus there is no change in energy to create them from themselves. Do NOT confuse standard state with STP

Equilibrium

Equilibrium is the state reached in the progress of a reversible reaction wherein there ceases to be any additional NET progress in either the forward or reverse direction. The reaction is still proceeding to a very small degree in both directions, but these movements cancel one another out Equilibirum is the rate going in the forward direction is the equal in the rate going backwards, but this doesn't mean the concentrations are the same, it just means concentrations wont' change anymore When a chemical reaction has attained the equilibrium state, the concentrations of reactants and products remain constant over time, and there are no visible changes in the system. However, there is much activity at the molecular level as the reactant molecules continue to form product molecules while product molecules react to yield reactant molecules. Chemical equilibrium is achieved when the rates of the forward and reverse reaction are equal and the concentrations of the reactants and products remain constant Under those exact conditions the entropy for that reaction is at its maximum possible value. Those conditions are also the lowest possible energy state for that reaction. Gibbs Free Energy will be exactly zero at equilibrium. This makes complete sense because the reaction would not proceed spontaneously in either direction because it is already at its most favorable state Students frequently confuse equilibrium with rate. For many students it seems intuitive (BUT IS ABSOLUTELY WRONG) that if a reaction has a large Keq this means the reaction "really wants" to reach equilibrium and will therefore proceed toward it quickly. You should be drilling into your students the conviction that equilibrium and reaction rate describe totally different things. Many reactions have high Keq values, but proceed very, very slowly. A high number for Keq simply tells us that at equilibrium there will be a lot more products than there are reactants. This tells us the reaction is spontaneous and will strongly favor the products side of the reaction, but tells us nothing about how fast it will get there. 1) At equilibrium, the rate of the forward reaction is equal to the rate of the backward reaction. 2) Since both reactions take place at the same rate, the relative amounts of the reactants and products present at equilibrium will not change with time. 3) The equilibrium is dynamic, i.e., the reactions do not cease. Both the forward and reverse reactions continue to take place, although at equal rates. 4) A catalyst does not alter the position of equilibrium. It accelerates both the forward and backward reactions to the same extent and so the state of

Titration of a WA w/ SB or WB w/ SA:

Equivalence Point/Stoichiometric Point = midpoint of the nearly vertical section of the graph at this point [titrant] = [analyte] However, because the acid and base are not both "strong" (i.e., dissociate 100% in water) the [H+] does NOT equal [OH-]. This also tells us that the pH does NOT equal 7 An MCAT question will simply ask: "What is the pH of the solution at the equivalence point?" or an answer choice will say "The concentration of hydroxide ions equals the concentration of hydrogen ions at point B." You will need to remember that the first thing you must do on such a question is decide which type of titration is being performed. For WB w/ SA: pH < 7 For WA w/ SB: pH > 7 For SA w/ SB: pH = 7

Titration of a SA w/ SB or SB w/ SA:

Equivalence Point/Stoichiometric Point = midpoint of the nearly vertical section of the graph. At this point [titrant] = [analyte]. For example, for a solution of NaOH being titrated with HCl, at the equivalence point [HCl] = [NaOH] in the flask. Put another way, the moles of HCl in the beaker = the moles of NaOH in the beaker. Because HCl and NaOH are both considered "strong" (i.e., dissociate 100% in water), they will both produce the same amount of ions per mole. Thus, for titrations involving a SA and a SB, [H+] = [OH- ] at the equivalence point (this is NOT true if a WA or WB is involved, as we'll discuss below). By definition, if [H+] and [OH- ] are exactly equal, pH = 7 at the equivalence point.

Quantum Mechanics

Every electron in an atom has a unique "address" or "location." Electron addresses consist of four numbers. One could think of the first number as giving the street name (i.e., shell), the second as giving the house or apartment (i.e., subshell), and the third as giving the room within that apartment (i.e., orbital). Electrons can come in pairs, with two electrons sharing one orbital. They are like two siblings sharing the same room. They are differentiated by their "spin." Quantum numbers 1, 2, 3, and 4 n, orbitals, # electrons in orbital, #electrons in shell so n=1, then ℓ=0, which there is 1 s orbital, and mℓ=0, and the fourth quantum number there are 2 max electrosn in 1s, and 2 electrons in the shell (2n^2) If n=2, ℓ=0,1 thus have 1 s orbital, mℓ= -1,0,+1, thus 3 different orientations, 3 different p orbitals, 2 electrons in 1s, and 6 electrons in 3p orbitals, and thus (2*2^2)=8 electrons in the shell n=3, ℓ=0,1,2, thus 1s, 3p, and 5d orbitals, mℓ= -2,-1,0,+1,+2=5 d orbitals, thus we have 18 electrons

Q34. For a reaction with two reactants, A and B, a graph of ln[A] vs. time is linear. How many of the following statements are true? 1) Reactant A must be first order, 2) Reactant B could be first order, 3) Reactant B cannot be impacting rate, 4) Reactant B must be in excess.

Getting a positive result (i.e., a line for one of the graphs) gives us much more information. Because the graph of ln[A] is linear we know that statement 1 is true, reactant A is indeed first order. We also know, however, that no other reactants are impacting rate. Statement 2 is NOT known. Reactant B could be first order; however, if it is first order then we know it MUST be in excess because only reactant A is impacting rate. Reactant B could also not be first order. It could be zero order and not impacting rate at all—an alternative explanation for why only reactant A is impacting rate. Statement 3 is known for this exact moment and set of conditions. Reactant B cannot be impacting the rate; if it were, the graph of ln[A] would not have been linear. Statement 4 is NOT known but could be true. We know that reactant B is not impacting rate, but that could be either because it is in excess or because it is zero order.

halogens

Halogens are the group 7A elements just to the left of the noble gases

Ion's in SOlution

Hydroxide, nitrate, nitrite, chlorate, chlorite, hypochlorite, perchlorate, carbonate, bicarbonate, ammonium, sulfate, phosphate, manganite, permanganate, and cyanide. OH⁻, NO₃⁻, NO₂⁻, ClO₃⁻², ClO⁻, ClO₄⁻, CO₃⁻², HCO₃⁻, NH₄⁺, SO₄⁻², PO₄⁻³, MnO, MnO₄⁻, CN⁻

Writing Rate Laws:

Know how to write a rate law, how to determine one from a table of experimental values, how to predict experimental results based on a given rate law. Rate laws assume the following: 1) Reactions only proceed forward (we ignore the reverse reaction) 2) We only consider the first few seconds of the reaction, when there is a high concentration of each reactant and any catalysts (e.g., enzymes). o Rate Law Exponents: Students often get the false idea that the exponents in the rate law are given by the coefficients in the balanced equation. The exponents equal the "order" of each reactant. Only if you are specifically told that the reaction is "elementary" do the coefficients equal the exponents in the rate law. For the MCAT, always assume that they do NOT. TEMPERATURE MATTERS, if temprature is given, you can only get a rate law from concentrations that have similar tempreature.

PV=nRT

R = 0.0821 L*atm/mol*K or 8.314 J/mol*K P= Pressure n= Moles V= Volume T- Temperature

R=K[A]^x[B]^y

R = Rate of rxn K= rate constant Orders determined experimentally by data. [A]^x= [B]^y= Overall order =3 https://www.khanacademy.org/science/chemistry/chem-kinetics/reaction-rates/v/rate-law-and-reaction-order

Radioactive Decay & Half Life

Radioactive decay is the process by which unstable atoms change their chemical composition over time The nucleus sometimes loses or gains electrons, lose bundles of protons and neutrons called "alpha particles," or even transforms one subatomic particle into another With the different types of DECAY- THINK OF NEUTRONS AS: neutron = a proton + an electron THINK OF PROTONS AS: proton = neutron + a positron

Oxidation Reduction Reactions

Redox rxns Any reaction where one or more e- are transferred from one atom to another The atom that LOSES e- is OXIDIZED and the atom that GAINS e- is REDUCED Example: Fe(s) + H₂O(l) -> H₂ (g) + FeO (s) --- Fe loses 2 e- and 2 H gain e-, Iron is thus the reducing agent and water is the oxidizing agent

Titration Curves: Strong Base with Strong Acid

With strong base present, the pH will start high. As strong acid is added, it will slowly go to lower pH and then sharply drop when the equivalence point is reached. Again, the middle of the pH region will be pH 7. It will then slowly go to lower pH as more strong acid is added. For SA w/ SB: pH =7

Solubility of Common Compounds

Remembering the following general rules will give you a quick shortcut to the right answer on several problems. 1) All compounds containing the following are SOLUBLE: nitrate, ammonium, and all alkali metals (Group IA). 2) All compounds containing the following are INSOLUBLE: (unless paired with something from the "always soluble" list above) carbonate, phosphate, silver (Ag), mercury (Hg), and lead (Pb).

Bohr Model of An Atom

Size of Components: A nucleus is made up of protons and neutrons held together by a strong residual force. Protons are positively charged, neutrons neutural, and about same size and mass. Electrons are much smaller, to the point that the electron cloud is mostly dead space. Charges: Protons are +, neutrons are neutral, electrons are - orbital filling corresponds to modern electron configuration diagrams—specifically to the number of electrons that can be held in an s, p, d and f orbital: 2, 6, 10 and 14. These numbers also match perfectly with the periodicity seen in the periodic table. Electrons can and do jump from one level to another if they receive the exact quantum of necessary energy and will release a photon equal in energy to the difference between two energy levels when they "relax" back to a lower energy level Electrons have both wave like and particle like nature, similar to light Electrons do not orbit the uncleus in circular patterns like rings Electrons have S, p d, and f orbitals with unique shapes

Solubility vs Solubility Product Constant

Solubility is a measure of "how much" of a solute can be dissolved in a given solute. For example, the solubility of iron(III)chloride in water is 74.4g/100mL The solubility product constant, or Ksp, is defined as the product of the dissolved ions in a saturated solution (i.e., at equilibrium) raised to their coefficients in the balanced equation. Ksp and solubility are directly related to one another (i.e., a large Ksp indicates a large solubility), but are not the same thing. An analogous comparison would be to ask "how much" of a strong acid will dissociate in 100mL of water and then compare that to the Ka of that acid. Because Ksp and solubility are not identical, a ranking of Ksp values for various substances may or may not match the order of a ranking of solubilities for those same substances. As an example, the solubility of NaCl is approximated by the square root of the Ksp (i.e., Ksp = [x][x]), but the solubility of CaCl2 is approximated by the cube root of one fourth of the Ksp (i.e., Ksp = [x][2x]2 = 4x3 ). Finally, the two quantities have different units.

SOlubility

Solute's tendency to dissolve in a solvent The amount of a solute that will dissolve in a given solvent at a given temperature. Temperature is usually specified because for most solids dissolved in liquids, solubility is directly related to temperature. On the MCAT, solubility is usually measured in either g/mL, g/100mL, or mol/L. "Like dissolves like:" This phrase refers to the fact that polar substances are soluble in polar solvents and non-polar substances are soluble in non-polar solvents. Polar and non-polar substances do NOT form solutions.

Bomb Calorimeter

Solve using: q = C∆T. This does NOT give enthalpy, but change in internal energy, ∆U or ∆E. Use heat capacity (big C) instead of specific heat capacity (little c). -utilizies constant volume, The bomb calorimeter is a sealed steel container, meaning volume cannot change. However, because volume is constant any gases produced or consumed during the reaction will change the pressure. bomb calorimeter is used to measure heat flows for gases and high temperature reactions. In a bomb calorimeter, the reaction takes place in a sealed metal container, which is placed in the water in an insulated container. Heat flow from the reaction crosses the walls of the sealed container to the water. The temperature difference of the water is measured, just as it was for a coffee cup calorimeter. Analysis of the heat flow is a bit more complex than it was for the coffee cup calorimeter because the heat flow into the metal parts of the calorimeter must be taken into account

Concentration Cell

Special type of Galvanic Cell A concentration cell is a limited form of a galvanic cell that has two equivalent half-cells of the same composition differing only in concentrations. One can calculate the potential developed by such a cell using the Nernst Equation. Same electrodes and solutions are used in both breaks One beaker, the metal is oxidized via oxidation half reaction Other beaker, it is reduced via reduction half-reaction The beakers use the SAME metals, thus E° cell is always E°cell = 0.00 V. Remember that E°Cell for a concentration cell, will ALWAYS equal 0, because you are using the same species for both the anode and cathode, for the reduction and oxidation half equation Based on this cell potential, it appears that nothing would happen. However, all E° values are given for standard conditions (the reason for the naught symbol). You do NOT need to know those conditions for the MCAT, but one aspect of standard conditions happens to be 1M concentrations for both solutions. Concentration cells are therefore nonstandard conditions by definition. They have a positive reduction potential E (no naught symbol, signifying nonstandard conditions) if there is a difference in the molarities of the two solutions. The Nernst equation is used to calculate the cell potential based off of the E˚ of the species and the concentrations of the two solutions. Yes, you do need to know the Nernst equation—it has shown up on the MCAT at least twice before.

Le Chatelier's Principle

Systems already at equilibrium, that experience change, will shift to the left or to the right to reduce the effects of that change and re-establish equilibrium. When you disrupt the equilibrium, creating a "shift" according to Le Chatelier's principle, what happens to Keq? Does it change? -Keq doesn't change, the value of equilibirum constant for the rxn does not change. Predict the effects of doing each of the following to a reaction at equilibrium: 1) adding/removing reactants- adding shifts right/ removing shifts left 2) adding/removing products- Adding shifts left, removing shifts right 3) increasing/decreasing pressure- Increasing pressure shift rxn to side with fewer moles of gas, decreasing pressure shift rxn toward side with more moles of gas 4) increasing/decreasing temperature.- Increasing temp changes Keq and shifts the rxn: -exothermic increase temp shift rxn to left and Keq decreases -endothermic rxn increasing temperature, shifts to the right and Keq increase -decreasing temp will have the exact opposite for each.

Constant Volume vs. Constant Pressure Heat Capacities

Systems can be confined by rigid walls (constant volume) or can be open to the atmosphere like water in a beaker (constant pressure Q3. What happens when heat enters a system? Does the temperature always increase? Is any increase in temperature always exactly proportional to the heat absorbed by that system? (Hint: Think of adding energy to a sealed steel container vs. adding energy to a balloon; remember that temperature is the average kinetic energy of the molecules.) PV work is the work necessary to produce an increase in volume. For example, when a sealed balloon is heated, the gases inside the balloon will expand and must do work on the rubber walls of the balloon and the air around it to accomplish this expansion. Because some of the heat energy added to the balloon was used for pv work, only the remaining portion of the heat will go toward increasing the average kinetic energy of the molecules (i.e., temperature). So, when heat enters a system, if the system is capable of volume change, heat can go to pv work, increased temperature, or both. For this reason, the addition of a certain amount of heat will NOT necessarily be exactly proportional to the resultant increase in temperature. Some of the temperature which is energy, is doing work or PV, thus energy is lost, the remaining energy goes directly to increasing temperature, but it has lost some of the energy due to work. If the system is not capable of changing volume then no pv work can be done, so all of the added heat will go toward an increase in temperature Q4. For the same system, which heat capacity will be greater, the constant volume heat capacity or the constant pressure heat capacity? If the volume is held constant, then 100% of the energy added will go toward an increase in temperature. If the pressure is held constant the volume can still change and therefore some of the added heat will go toward pv work. If we think of heat capacity as "the amount of energy we can add before the system increases by one temperature unit," it is fairly easy to see that the system capable of pv work will be able to absorb more heat before increasing by one degree Celsius or Kelvin. It is much like asking how many gallons of water can be added to Tank A vs. Tank B? Tank A and Tank B are both 5-gallon tanks, but Tank B is connected via a hose to a reserve tank that holds 2 gallons. So, you can add 5 gallons to Tank A before it is "full" (analogous to a one unit increase in temperature). However, you can add 7 gallons to Tank B before it is full (the reserve tank being analogous to pv work). We would therefore say that Tank B has the higher "water capacity" in terms of our analogy. This indicates that the constant pressure heat capacity (allows for pv work; i.e., includes the 2-gallon reserve tank) will be more than the constant volume heat capacity (does not allow for pv work; i.e., no reserve tank) for the same system.

Condosity:

The "condosity" of a solution is the concentration (molarity) of an NaCl solution that will conduct electricity exactly as well as the solution in question. For example, for a 2.0 M KCl solution, we would expect the condosity to be something more than 2.0. Why would we expect it to be above 2.0? Because potassium is more metallic than sodium. Thus, we know that it will be a better conductor. This means the NaCl solution will have to be slightly more concentrated in order to conduct electricity as well as the KCl solution. (look at metallic character, more metallic character, it's a better conductor... ALWAYS COMPARING TO SODIUM CHLORIDE Q16. What is the expected condosity of a 3.0 M LiCl solution? Sodium is more metallic than lithium, so we would expect an NaCl solution to conduct electricity better than an equimolar LiCl solution. This means the NaCl solution would need to be less concentrated in order to conduct equally as well. This predicts a condosity of something less than 3.0 for a 3.0M LiCl.

Real Gases

THe Greatest Deviation between ideal gas behavior and real gas behavior occurs when: a) temperature is extremely low--- produce smaller pressure than predicted by ideal gas law b) the pressure is extremely high--- gas molecules occupy greater volume At very high pressure, the molecules are pushed really close together, and their actual size becomes comparable to 0, meaning there is no distance between them. At every low temperature- the interaction of gas molecules becomes more important. Both cases result in deviations from ideal gas low 2) Increase inter-moleculer attractions decreases pressure in real gases, aka large a' = small P --- If PV/nRT > 1 it is due mostly to the molecular volume assumption 3) Increased molecular volume, increases volume in real gases --- If PV/nRT < 1 it is due mostly to the inter-molecular forces assumption In real gases volume is MORE than would be predicted by the ideal gas law because real molecules do occupy some volume. Notice that this is an INCREASE. By contrast, in real gases pressure is LESS than predicted by the ideal gas law. This is because real molecules do experience intermolecular attractions—forces that tend to slow down the molecules as they collide with the walls of the container and therefore pressure. Notice that this is a DECREASE. Looking at the ratio PV/nRT, we see that both pressure and volume are in the numerator. As a result, the "real" deviations just described that increase volume will cause PV/nRT to increase to greater than one, and "real" deviations that decrease pressure will cause PV/nRT to decrease to less than one. Thus use Van der Waals Equation, but not important for MCAT

Group/family

THe Vertical column

Critical Pressure

THe pressure at the critical point the highest vapor pressure that a liquid can have (the vapor pressure of a liquid at the critical temperature)

To calculate the "order" of each reactant using experimental data:

The "overall order" of a reaction = the sum of the exponents in the rate law

Salt of Weak Acid

The "salt of a weak acid" refers to the conjugate base of that weak acid combined with a cation to form a salt Conjugate base + cation for weak acids HCO3- = "weak acid"; CO3^2- = "conjugate base"; Na2CO3 = "salt of a weak acid" Na2+ is the cation forming the salt with the conjugate base When the salts of weak acids or weak bases dissolve in water one of the ions will undergo hydrolysis to re-form the weak acid or the weak base: 1) Na2CO3 <-> 2Na+ + CO3^2- 2) CO3^2- + H2O <-> HCO3- + OH-

Period

The HOrizontal row

Heisenberg Uncertainity

The Heisenberg Uncertainty Principles states that the more we know about an electron's position, x, the less we know about its momentum, p.

Kinetic Theory of Gases

The MCAT authors have shown a clear affinity for test questions that address the contrasts between "ideal" behavior and real behavior We compare ideal behavior vs real behavior KNOW THE FOLLOWING: - cALCULATING A PROJECTICLE'S MOTION IGNORING AIR RESISTANCE but also how it is changed uner real conditions - THis is similar when dealing with ideal fluids vs real fluids - Ideal gases vs real gases

Effusion (Graham's Law)

The diffusion of gas particles through a pin hole A pin hole is defined as a hole smaller than the average distance a molecule travels between collisions E1/E2=√MW2/√MW1

ΔHsolution

The enthalpy value associated with the dissolution of a species into solution The enthalpy change of solution is the enthalpy change when 1 mole of an ionic substance dissolves in water to give a solution of infinite dilution.

ΔHfusion

The enthalpy value associated with the phase change from liquid to solid. The sign changes for the reverse process (melting). the energy that must be supplied as heat at constant pressure per mole of molecules melted (solid to liquid).

ΔHcombustion

The enthalpy value for the combustion of a compound with O2 to form CO2 and water. The standard enthalpy change of combustion of a compound is the enthalpy change which occurs when one mole of the compound is burned completely in oxygen under standard conditions, and with everything in its standard state. A high heat of combustion is associated with an unstable molecule a low heat of combustion with a stable molecule.

ΔHformation

The enthalpy value for the formation of a compound from its elements in their standard states. If the number is negative, formation is an exothermic process, if it is positive, the process is endothermic.

Molar mass

The mass in grams of 1 mol of a substance.

Metallic Character

The metallic character of an element can be defined as how readily an atom can lose an electron. From right to left across a period, metallic character increases because the attraction between valence electron and the nucleus is weaker, enabling an easier loss of electrons. Metallic character increases as you move down a group because the atomic size is increasing. When the atomic size increases, the outer shells are farther away. The principle quantum number increases and average electron density moves farther from nucleus. The electrons of the valence shell have less attraction to the nucleus and, as a result, can lose electrons more readily. This causes an increase in metallic character.

. For a reaction with two reactants, A and B, a graph of 1/[A] vs. time is non-linear. Which of the following is known? 1) The reaction cannot be second order in A and independent of B, 2) Reactant B must be involved in the rate law, 3) Reactant B cannot be in excess.

The observation that a graph of 1/[A] is non-linear is somewhat inconclusive. The graph could have been non-linear because both reactants are impacting the rate (violating the rule that these graphs will only be linear if only one reactant species is impacting rate). However, it could also be non-linear if reactant A is the only reactant impacting rate, but reactant A is not second order. For example, suppose that reactant A is actually first order; the graph of 1/[A] would not be linear, but the graph of ln[A] would be. Statement 1 is the best choice because if reactant A was second order and reactant B did not impact rate, we would expect a linear plot. Statement 2 is NOT known. Reactant B could be in the rate law and that is why the graph is not linear; however, it is equally plausible that reactant B is NOT in the rate law and the graph of 1/[A] is not linear because A is first order, not second order. Statement 3 is NOT known either. As we have already explained, the graph could be linear either way. If reactant B is in excess then the graph could be non-linear because reactant A is actually first order, not second order. If reactant B is not in excess (and is in the rate law) then the graph could be non-linear because both A and B are impacting rate.

Impact of Salts on the Dissolution of Weak Acids and Weak Bases

The percent dissociation of benzoic acid (weak acid) decreases in a sodium benzoate solution. -In case one, sodium benzoate dissociates to release benzoate ions, which shift the acid dissociation equilibrium for benzoic acid to the left. The percent dissociation of ammonium hydroxide (weak base) decreases in an ammonium chloride solution -Similarly, ammonium chloride dissociates to release ammonium ions, which shift the base dissociation equilibrium for ammonium hydroxide to the left. SO basically, Ammonium chloride is already dissociating, thus shifting the solution to make it more basic, so ammonium hyrdoxide won't have an effect.

Gas Solubility

The solubility of gases in liquids follows a trend that is exactly the opposite of the solubility of solids in liquids. For gases dissolved in liquids, increased temperature decreases solubility and decreased temperature increases solubility. o Increasing the vapor pressure of gas X over a liquid increases the solubility of gas X in that liquid (This is why they pressurize soda pop cans with excess CO2). o Polar and non-polar gases easily form homogenous mixtures.

Molecular Weight

The sum of an atomic weight of a molecule's component atoms

Boiling Point

The temperature at which boiling occurs; the temperature at which the liquid and vapor phases of a substance are in equilibrium. the temperature at which a substance changes state from liquid to gas. Liquids boil when the vapor pressure of the liquid equals atmospheric pressure.

Enzyme vs Catalyst

The word catalyst is a more general term for any substance that increases the rate of a reaction without being altered or consumed during the process. An enzyme is one type of biological catalyst. Enzymes are long protein chains folded into complex tertiary structures that feature an active site that is unusually specific to the reactants and/or transition state of the reaction it catalyzes It could be said that all enzymes are catalysts, but there are many catalysts that are not enzymes. In fact, the catalysts you will encounter in general chemistry are almost always inorganic compounds or solid metals. Some texts define "catalyst" as being inorganic molecules that catalyze reactions, and enzymes as being organic molecules that catalyze reactions. However, because an enzyme is still "catalyzing" a reaction, we think the use of the term "catalyst" as a more categorical term makes the most sense.

Theoretical Yield

Theoretical Yield: the amount of product in grams that would be produced if the reaction ran 100% to completion. In other words, you take your limiting reagent, do a mole-to-mole conversion to get moles of product, and then convert that to grams. Actual Yield: Actual yield is just what it sounds like, the amount of product in grams you obtain at the end of the actual experiment in the lab Percent Yield: The percent yield is just the ratio of the actual yield over the theoretical yield multiplied by 100. Remember that yield is a function of reactants and equilibrium, NOT rate, FOCUS ON THESE TWO WAYS TO INCREASE YIELD: 1) Start with more reactants 2) Shift the equilibrium to the right using one of the actions described by Le Chatelier's Principle The most common method of shifting the equilibrium in this way is to remove products as they are formed. By doing so, you force the reaction into a constant state of "catch up." The reaction continually produces more product in an attempt to reach equilibrium. CAVEATS: Action 1) above will increase overall quantity of yield, but NOT percent yield. Furthermore, it will only work if you add more of the limiting reagent. Adding more of any non-limiting reagent (i.e., a reagent that is in excess) will have no effect. Moles of Oxygen Needed for Combustion: You will occasionally be asked to predict the species that will require the most oxygen to combust. Here is a simple ranking system to make such predictions quickly: o Add 1.0 for each carbon and subtract 0.5 for each oxygen. The higher the resulting number the more oxygen necessary for full combustion. This is NOT, however, the actual number of moles required—this is only a ranking system. The only way to determine the exact moles of oxygen required for a combustion reaction is to write out and balance the combustion equation.

Solving Half-Life Problems

There are three variables involved in half-life problems: half-life, t1/2, time elapsed, t, and the amount of the substance in grams, g. You are usually given two of those three and asked to solve for the third. Try to do this conceptually in your head—do not use a formula. For example, one question may tell you that we currently have 500 g of element Z, and that the half-life of element Z is 10 years. It then asks how much of element Z will remain 40 years from now. The half-life tells us that every 10 years the substance is cut in half. Thus, in 40 years it will be cut in half four times. Write 500 g on your scratch paper, then cut it in half four times to get the correct answer: 31.25 g. Another question may give you the initial and final mass of the substance plus the amount of time elapsed, and ask you to calculate the half-life. In such a case: -first decide how many times the substance had to be cut in half to go from the initial value to the final value (i.e., the number of half-lives). - Divide the total time elapsed by the number of half-lives to get the length of each half-life Always take notes when counting half-lives. Many students make silly errors because they miscalculate the number of half-lives. Write it down and you won't mess up! This is yet another application of the Altius mantra: Write it Down and Draw it Out!

ΔH RXN the enthalpy change for a reaction:

This is usually calculated by adding reactions (and their associated enthalpy changes) from a table. You must select the reactions from the table that—when added together—will produce the net reaction for which you are calculating ∆HRXN. To calculate ∆HRXN you will add all of the values given for each of the reactions you use, paying careful attention to signs and stoichiometry. If the reaction proceeds in the same direction as it would in the net reaction, use the value given directly. If it proceeds in the opposite direction, change the sign of the value given. You MUST multiply the number given in the table by the coefficient in the balanced net reaction. For example, suppose one of the reactions given was the formation of liquid water from the elements hydrogen and oxygen: 1/2O2 + H2 -> H2O ∆H° f = -285 kJ/mol, but in your net reaction water is a reactant rather than a product. You would need to change the sign of ∆H° to be positive and combine it with the enthalpy changes from the other reactions used. If your balanced net reaction contained two moles of water, you would need to double the value given, and so forth.

Equilibrium Constant

This situation we call "equilibrium" is described mathematically by the ratio of products over reactants present at that exact point. We calculate that ratio using the law of mass action and the resulting number we call Keq. We like students to think of Keq as exactly that—a mathematical number used to define/describe/label equilibrium. This works nicely because this state of maximum "happiness" for the reaction in terms of energy and entropy is dependent on a certain ratio of reactants to products. If the amount of either of these changes, the number we calculate for Keq will also change and then we will know that we are no longer at that ideal set of conditions (In fact, the minute that number changes we don't even call it Keq anymore, we call it Q instead).

Titration Curves: Weak Base with Strong Acid

This will look like the strong base/strong acid titration except the pH will not start as high, the equivalence region won't last for as many pH units, and the equivalence point will be at a pH below 7. For WB w/ SA: pH < 7

Q35. Describe how you could use the rate order graphs to determine the order of each reactant in a multi-reactant reaction experimentally in the lab: What would you need to measure? What would you do with the data?

To determine the order of each reactant experimentally you would only need to ensure that all other reactants were in excess and measure the concentration of the limiting reactant as a function of time. You would then use the measured concentration of the reactant in question in each of the types of graphs. If all other reactants are in excess, one of these graphs should be linear. You may be tempted to think that you wouldn't get a positive result if the reactant you were testing was NOT impacting rate. However, that would produce a line for [A] vs. time (i.e., the reaction would zero order in that species). Remember that zero order reactants are not included in the rate law!

Transition Metals

Transition metals are the elements in the four middle rows

Hydration

Water molecules attached to ionic units in a solid

Mole-to-mole Conversion:

We have found that students perform much better on these problems if they have a map already in their head of where they can go. We do not want you to memorize the flowchart shown below. However, if you can internalize it naturally you will always be able to plan out exactly how to move from what you are given to what you need to calculate

Weak Acids

Weak acids and bases do not dissociate readily in solution. As a general rule, an acid with a pKa greater than zero, or a Ka less than one, can be considered a weak acid. Similarly, a base with a pKb greater than zero, or a Kb less than one, can be considered a weak base. Examples of Weak Acids: Anything NOT on the strong acid list. - H2O, H2S, NH4+, HF, HCN, H2CO3, H3PO4, acetic acid, benzoic acid, etc.

Weak bases

Weak acids and bases do not dissociate readily in solution. As a general rule, an acid with a pKa greater than zero, or a Ka less than one, can be considered a weak acid. Similarly, a base with a pKb greater than zero, or a Kb less than one, can be considered a weak base. Examples of Weak Bases: Anything NOT on the strong base list. H2O, NH3, R3N, pyridine, Mg(OH)2, etc.

Acid/Base Clarification

When we add an acid or base to water, the equilibrium of that acid or base will directly impact the equilibrium for the ionization of water according to Le Chatelier's Principle Notice that the addition of either an acid or a base shifts the equilibrium for the ionization of water to the left! The equilibrium for the ionization of water is always present in aqueous solutions. Adding an acid shifts the reaction to the left, and increases the relative [H+] Adding a base shifts the reaction to the left, and increases the relative [OH-] Kw, Ka and Kb are used to describe these three equilibriums. At 25°C, Kw = Ka*Kb; this should make sense because 1) we demonstrated above that this is mathematically true, and 2) if we always remain at 25°C the Kw for the ionization of water should never change—per our rule that temperature is the only thing that changes Keq.

Solving Ideal Gas Law Problems

Whenever you see more than one of the above variables together in the same problem (i.e., T, P, n and/or V), you are most likely dealing with an Ideal Gas Law problem. There are two ways you can approach these problems: 1) Manipulating Equations- PV=nRT 2) P1V1/T1 = P2V2/T2 (combined gas Law --Because PV/T = nR, and R is a constant, given the same number of moles of gas, the ratio of PV/T must remain constant, regardless of the changes made to the system. -- You can choose the first set of data as being STP, or as any other point where P, V and T are known. The second set of data will be different, but the ratio will always be the same. --- Plug in the data and solve for the unknown. Conceptually, you're probably better off if you understand and can apply the first method.

Calculating Solubility

Write out the Ksp expression. Substitute into the expression the value given for Ksp. Substitute a factor of x into the equation for the concentration of each ion, using 2x, 3x, etc., if more than one mole of each ion is produced (Hint: Ask yourself, "If x moles of the reactant are dissolved, how many moles of each ion will be produced?"). Solve for x. Your answer, "x" is the "solubility" of that particular specie.

Calculating ΔHRXN Using Bond Energies:

You can also calculate the enthalpy change of a reaction using bond energies To do so, simply add up the bond energies of all of the products and reactants. If a bond is broken during the reaction, energy is required, so the bond energy should be given a positive sign. If a bond is formed, energy is released, so the bond energy should be given a negative sign Bonds made= - Bonds broken= + Once again, multiply all bond energy values by their coefficients in the balanced equation.

Activation Energy (Ea)

You can think of the activation energy as a barrier to the reaction. Only those collisions which have energies equal to or greater than the activation energy result in a reaction. Remember that for a reaction to happen, particles must collide with energies equal to or greater than the activation energy for the reaction

The Atom

Z= Atomic number, the number of protons, this is what defines an element A= mass number, which is protons + neutrons

Zero Order

[A] vs. time is linear (i.e., yields a straight line) with slope = -k zero order is not included in the rate law, so if [A]^0, then the rate law would only be be shown as R=K Putting it in excess makes it effectively zero order under those conditions and any effect remaining must be due solely to only ONE reactant

Van Der Waal's equation

[P + a'(n/V)² X [(V/n)-b']= RT a' is a constant that represents the actual strength of intermolecular attractions b' is a constant that represents the actual volume of molecules The Van der Waals equation has never been on the MCAT and it should NOT be memorized. We present it here because it demonstrates a few important principles you should know for the MCAT: 1) Rules for manipulating Equations, you cannot use manipulating equation skills we presented on an equation that involves addition or subtraction 2) Increase inter-moleculer attractions (a') decreases pressure in real gases, aka large a' = small P 3) Increased moleculer volume (b') increases volume in real gases

Non-volatile

a substance that has no measurable vapor pressure the substance does not form a vapor, or has an extremely low vapor pressure, at room temperature. This usually refers to solutes such as sodium chloride that do not contribute to the vapor pressure of a solution when dissolved in a solvent. By contrast, something like methanol would have its own vapor pressure that would add to the vapor pressure of the solvent into which it is dissolved.

Absolute Temperature

a temperature measured from absolute zero in Kelvins An absolute temperature is any temperature measured relative to absolute zero. The Kelvin scale is measured relative to absolute zero, where absolute zero is defined as 0 degrees Kelvin—therefore all Kelvin temperatures are absolute. Absolute zero is a theoretical temperature limit where all molecular motions cease ABSOLUTE TEMPERATURE= NO MOLECULE MOTION

Entropy

a thermodynamic quantity representing the unavailability of a system's thermal energy for conversion into mechanical work, often interpreted as the degree of disorder or randomness in the system.

Single Displacement Reaction

a type of oxidation-reduction chemical reaction when an element or ion moves out of one compound and into another-that is, one element is replaced by another in a compound.

f-block

d the f-block is the lanthanides and actinides which actually occur in order between the s-block and d-block elements on rows 6 and 7 respectively.

How does the addition of a non-volatile solute affect vapor pressure?

decreases. it occupies a portion of the surface area available for vaporization 2) non-volatile solute- ---↑ non-volatile= ↓Vp due to n.v. occupies portion of limited surface area for vaporization. This causes liquid molecules unable to exit due to non-volatile solutes stopping the exit ports. ---Vp = XVp° ---Vp + n.v.s= some fraction of vapor pressure for pure solvent, X= mole fraction, Vp equal actual Vp, and Vp°= Pure solvent Vp

Isotopes

each of two or more forms of the same element that contain equal numbers of protons but different numbers of neutrons in their nuclei, and hence differ in relative atomic mass but not in chemical properties; in particular, a radioactive form of an element. Isotopes of an element will contain the same number of protons and electrons but will differ in the number of neutrons they contain. In other words, isotopes have the same atomic number because they are the same element but have a different atomic mass because they contain a different number of neutrons An isotope is one of multiple versions of the same atom that have differing numbers of neutrons. All isotopes must have the same Z number because it is the number of protons that defines the atom as a specific element (carbon, hydrogen, etc.). If you know the Z number you know the element. All isotopes do not have an odd mass number (carbon-14), although many do (iron-57). For example, carbon is normally present in the atmosphere in the form of gases like carbon dioxide, and it exists in three isotopic forms: carbon-12 and carbon-13, which are stable, and carbon-14, which is radioactive.

Electrolytic Cell

electrolysis is a technique that uses a direct electric current (DC) to drive an otherwise non-spontaneous chemical reaction. Electrolysis is commercially important as a stage in the separation of elements from naturally occurring sources such as ores using an electrolytic cell. It is a galvanic cell to which an external voltage is applied, forcing the electrons to flow in the OPPOSITE direction Oxidation still occurs at the anode and reduction at the cathode The species with the LOWER reduction potential will be REDUCED, unlike the galvanic cell- ex= .32V vs .88V, .32V has lower reduction potential is thus reduced and .88V is oxidized The cell potential E° cell will ALWAYS be negative The sum of the externaly applied voltage (V battery) and the negative cell potential (-E° cell), in volts, must be positive Cathode= (-) Anode= (+) reduction still ALWAYS happens a the cathode This is different compared to galvanic cells

Electron Affinity

electron affinity is the ability of an atom to accept an electron Electron affinity generally decreases down a group of elements because each atom is larger than the atom above it With a larger distance between the negatively-charged electron and the positively-charged nucleus, the force of attraction is relatively weaker. Therefore, electron affinity decreases. Moving from left to right across a period, atoms become smaller as the forces of attraction become stronger. This causes the electron to move closer to the nucleus, thus increasing the electron affinity from left to right across a period.

Noble Gases

noble gases are the group 8A elements on the far right of the table

Limiting Reagent

o You must have a balanced equation. o You must convert to moles first. o Compare the number of moles you have to the number of moles required to run one cycle of the reaction, as indicated by the coefficients. The reactant you will run out of first is the limiting reagent. o The reactant you have the least of, in either grams or moles, is NOT necessarily your limiting reagent. For example, suppose for the combustion of methane you have 1.5 moles of O2 and only 1.0 mole of methane. Because you need two moles of O2 to react with one mole of methane, you will run out of O2 first and it is therefore your limiting reagent—even though you have more moles of O2 than you do methane. https://www.khanacademy.org/science/chemistry/chemical-reactions-stoichiome/limiting-reagent-stoichiometry/v/limiting-reactant-example-problem-1

Third Quantum Number

o a.k.a. "mℓ" or "the magnetic quantum number" o Gives the orbital orientation; has a value of -ℓ to ℓ (from the azimuthal quantum number) Designates the orientation of the subshell where an electron is most likely to be found (i.e., which "dumbbell" of a p subshell) The orientation of the orbital around the nucleus mℓ= -ℓ to +ℓ So if ℓ=0, then mℓ=0, means there is only one orientation around the nucleus, and a sphere only has one orientation around the nucleus ℓ=1, mℓ= -1, 0, +1, 3 possible values, this tells us that there are 3 possible orientations. We have 3 possible orientations for the p orbital, or the dumbbell shape.

∆G° = - RTlnKeq

relates the equilibrium constant to the Gibbs free energy (Note: Remember that the ln of any positive number less than 1 is negative). A useful rearrangement of the above equation: Keq = e^-ΔG/RT Q15. If the value of Keq is known, what can we infer about ΔG°? If a reaction is spontaneous, what can we infer about the rate of that reaction? If the value of K is greater than one then the reaction will be spontaneous. To be more precise, if we are starting at the standard state conditions, then we know the reaction will proceed spontaneously. We know this because the natural log of a number greater than one is positive, which will result in a negative Gibbs Free Energy per the equation given. If the value of K is less than one then the reaction will not proceed spontaneously from standard state conditions. We know this because the natural log of a number less than one is negative. This negative will counteract the existing negative in front of the equation and therefore the sign of Gibbs Free Energy will be positive. If K = 1, then ∆G = 0 because the natural log of one is zero. Again, a key principle in this section is that kinetics is "walled off" from thermodynamics: the value of K will not tell us anything at all about the rate of the reaction.

Heat of Combustion

the amount of energy released when a molecule is combusted with oxygen. All covalent bonds are broken and reformed in a radical reaction. The higher the energy of the molecule (i.e., less stable) the higher the heat of combustion. LESS STABLE BONDS=LOW ENERGY BONDS=HIGH ENERGY MOLECULE=HIGHER HEAT OF COMBUSTION Why do bonds form? Is energy required or released when a bond is formed? -Atoms are without feelings and don't "want" to form bonds. They only do so in situations where the resulting bond is a lower energy state than was the unbonded form (or than the previous bonds they were engaged in with other atoms) As a result, FORMING BONDS ALWAYS RELEASE ENERGY. This is a major point of confusion for students. ATP is often the molecule that exacerbates this confusion. The transition from ATP to ADP does release energy, but only because the forming of the new bonds in ADP releases more energy than was required to break the bonds in ATP—NOT because breaking the bonds in ATP released energy. FORMING BONDS RELEASE ENERGY

Critical Point

the precise temperature and pressure above which liquid and gas phases become indistinguishable. At this point liquid and gas phases cease to exist, merging into a single phase called a super critical fluid liquid and gas phases cease to exist, merging into a single phase

Solvation

the process of surrounding solute particles with solvent particles to form a solution process wherein solvent molecules surround a dissolved ion or other solute particle creating a shell. Hydration is a specific kind of solvation wherein water is the participating solvent. Water molecules, being polar, can surround both negatively and positively charged solutes by directing either their partially-negative oxygen, or partially positive hydrogen, moieties toward the ion.

Critical Temperature

the temperature at the critical pont temp at the critical point; above this temp the vapor can't be liquified at any pressure

Melting Point

the temperature at which a solid changes into a liquid the temperature at which a substance changes state from solid to liquid. However, it is very important to realize that melting point and freezing point are exactly the same thing. You might think of freezing point as the temperature at which a liquid changes into a solid, but the value measured for mp or fp is simply a temperature, which indicates no direction of progress. For any substance, mp = fp.

Thermodynamics

the thermodynamics of a reaction reflect the potential reactivity (for example, given infinite reaction time) and includes all measurements of energy flow and relative stability. ∆H ∆G ∆S Keq A simple, but effective conceptual approach to thermodynamics is to think of it as differences in energy across a reaction. If the bond energies of the reactants are lower than the bond energies of the products, then the products are by definition more stable. We would expect therefore, that as the molecules transform from a less stable state to a more stable state there would be a release of energy (i.e., an exothermic process). If the reverse is true we would expect that energy would be required (i.e., endothermic) to drive the molecules from a more stable state (higher BE) to a less stable state (lower BE). Entropy works in a similar way, but it is a measure of randomness or disorder and has the units of energy/temperature (J/K). It requires energy to create order. Conversely, there is an energy release associated with going from a more ordered state to a less ordered state. Gibbs free energy combines these concepts and represents the total free, available energy either produced or required by a reaction as a function of BOTH changes in the bond energies (∆H) and changes in the entropy state (∆S). It is IMPERATIVE that students understand that the rate of a reaction is independent of its thermodynamic properties.

Coffee Cup Calorimeter

use q=mc∆T c= specific heat capacity NOT HEAT CAPACITY - When a chemical reaction occurs in the coffee cup calorimeter, the heat of the reaction if absorbed by the water. The change in the water temperature is used to calculate the amount of heat that has been absorbed (used to make products, so water temperature decreases) or evolved (lost to the water, so its temperature increases) in the reaction. -Utilized constant pressure, The coffee cup calorimeter allows for an increase in volume of the solution inside the coffee cup, but remains at atmospheric pressure throughout -A coffee cup calorimeter is a constant pressure calorimeter. As such, the heat that is measured in such a device is equivalent to the change in enthalpy. A coffee cup calorimeter is typically used for solution based chemistry and as such generally involves a reaction with little or no volume change. A coffee cup calorimeter is great for measuring heat flow in a solution, but it can't be used for reactions which involve gases, since they would escape from the cup.

KE = E - φ

where E is the amount of energy added or photon energy KE is the kinetic energy of the ejected electron The amount of energy required to do this is called the "work function," and is usually given the variable φ, or the work function of the metal E can be replaced with hf, the formula for energy of a proton One of the most important take-home messages is that more INTENSE light [i.e., same wavelength, but more photons striking the metal per second] does NOT increase the KE of ejected photons, but DOES increase the number of photons ejected. Meanwhile, changing to a higher frequency light [i.e., blue light replacing red light] DOES increase the KE of the ejected electrons [as long as the work function has been exceeded].) Light intensity or wavelength does not increase KE, only increases # photos ejected Higher frequency DOES affect speed or KE of photons being ejected ex- 700J at a rate vs 1 X 10^5 protons vs 350J and a rate of photos at twice the first rate, means that the second source will eject twice as many electrons as the first. The left energy will be KE, which can be used to solve for velocity using 1/2mv^2=KE

w=−pΔV

where P is the external pressure on the system, ΔV is the change in volume. This is specifically called "pressure-volume" work

KE = 3/2kBT

where kB is Boltzmann's constant; this shows the direct relationship between temperature and kinetic energy) Temperature = The average kinetic energy of the molecules. Many questions, for example, substitute a phrase such as "an increase in the average kinetic energy of the molecules" for the phrase "increase in temperature." Most students who read that phrase will not immediately recognize it as another way of saying "temperature." Increase in Avg KE= Increase in tempreature

Gibbs Free Energy (∆G)

∆G = the amount of "free" or "useful" energy available to do work (excluding pv work ΔG can predict the direction of the chemical reaction under two conditions: constant temperature and constant pressure. If energy is available and the system can do work, Gibbs Free Energy is negative If energy must be added to the reaction (e.g., heat must be added to the system) to make it proceed, Gibbs Free Energy is positive. o Units: Joules Spontaneous - is a reaction that is consider to be natural because it is a reaction that occurs by itself without any external action towards it. Non spontaneous - needs constant external energy applied to it in order for the process to continue and once you stop the external action the process will cease negative ∆G = Spontaneous process; free energy available to do work. -ΔG<0 : reaction is spontaneous in the direction written (i.e., the reaciton is exergonic) positive ∆G = Non-spontaneous process; no free energy available; energy is required. -ΔG>0: reaction is not spontaneous and the process proceeds spontaneously in the reserve direction. To drive such a reaction, we need to have input of free energy (i.e., the reaction is endergonic)

Important signs of Enthalpy, Entropy, Temperature, Gibbs

∆G = ∆H - T∆S +∆S = increased randomness, and thus more energy available to do work. becoming less ordered -∆S = decreased randomness, and thus less energy available to do work., becoming more ordered -ΔG<0 : reaction is spontaneous in the direction written (i.e., the reaciton is exergonic) (ΔG is negative) +ΔG>0: reaction is not spontaneous and the process proceeds spontaneously in the reserve direction. To drive such a reaction, we need to have input of free energy (i.e., the reaction is endergonic) (ΔG is positive) +ΔH>0: Endothermic reaction -ΔH<0: Exothermic Reaction When temperature is high, entropy is favored When temperature is low, entropy isn't favored

Relationship between Free energy and Chemical Energy

∆G° = -nFE° ---n = number of moles of ELECTRONS transferred in a BALANCED redox reaction --- F= Faradays constant Faraday's Constant = the charge on one mole of electrons. positive E˚ = negative ∆G = spontaneous reaction A positive Cell potential means that a species will WANT to be reduced, it is more spontaenous towards a redox reaction, this looking at the equation, that is why a + E˚ = -∆G, which a -∆G is a spontaneous rxn.