Chem 2 exam 3
In thermodynamics, coupling reactions means:
"coupled reaction" is defined as "one that involves two separate processes that can be combined to give a single reaction. In most cases, a thermodynamically unfavorable reaction is combined with a thermodynamically favorable reaction to give an overall reaction that is thermodynamically favorable."
solubility vs solubility product
"solubility is referring to the value of X in change column. "solubility product" is referring to value of Ksp
Electrolytic cell problem equation
(ampers*seconds)/(96485*electrons)= mol substance
What do you do if a ligand name already includes a prefix
(e.g. ethyleneDIamine) use bis-, tris-, or tetrakis-, to indicate two, three. or four ligands. when doing this put the ligand name in parentheses: tris(ethylenediamine)
entropy and phase changes.
-Going from a liquid to a gas results in the greatest increase in entropy, due to the huge positional freedom that molecules of gas have vs. molecules of liquid. -Going from a solid to a liquid results in an increase in entropy, due to some molecules breaking free, but this change is small as compared to going from a liquid to a gas in which all of the molecules break free. -Heating the liquid results in an increase in entropy due to an increase in kinetic energy, rotational energy and vibrational energy, but this change is small as compared to going from a liquid to a gas. -Heating the gas results in an increase in entropy due to an increase in kinetic energy, rotational energy and vibrational energy, but this change is small as compared to going from a liquid to a gas. -Heating the solid results in an increase in entropy, due to an increase in kinetic energy, rotational energy and vibrational energy, but this change is small as compared to going from a liquid to a gas.
Key components of voltaic cell
-electrodes -anode -cathode -salt bridge
"A saturated solution contains 0.44 g dissolved in a total of 300.0 mL of solution. Calculate Ksp
-find molar weight of substance -convert mass given, using molae weight to mol. -divide by volume given to get M solve the problem as you would usually by making equation, ICE table and usuing found M as value for X
The entropy of a substance depends on what?
-molar mass -physical state (s,l,g,aq) -molecular complexity allotropes
naming and numbering negatively charged complex ions
-name the ligand and establish the charge of the central metal cation as before -name the central metal by dropping the ending of the metal and adding -ate followed by the oxidation state written in roman numerals -some metal names use their latin root (SEE NOTES)
naming and numbering positively charged complex ions
-name the ligand as stated previously -name the central metal: be sure to include the charge in the name using roman numerals if its a transition metal and has moe than one oxidation state. -charge of the cation must be established based on the charges of the ligands (and counterions) present
nonstandard free energy change (ΔG)
-partial pressure of gases are other than 1 atm -concentration of dissolved species are other than 1M
solubility relative to Ksp
-the smaller the KSp, the less soluble it is. (comparing compounds of same number of ions. -solubility: value of X -if X is big: greater solubility -the smaller the X: lower molar solubility.
formula that we dont need
-w=qE
standard free energy change (ΔG°)
-when all reactants and products are in their standard states -partial pressure of each gas is 1 atm -concentration of each dissolved species is 1M
steps for balancing a Redox Reaction under acidic conditions
1. assign oxidation numbers to all species 2. separate the overall reaction into an oxidation half and reduction half 3. for each half reaction balance all atoms except H and O 4. balance oxygen by adding H2O 5. balance hydrogen by adding H+ 6. balance the charge of the oxidation half by adding (e-) to the RIGHT so both sides of the equation have the same charge 7. balance the charge of the reduction half by adding (e-) to the LEFT so both sides of the equation have the same charge 8. multiply through one or both half-reactions by a necessary numbers so that the number of electrons in both half-reactions are the same 9. add up half reactions and cancel species appropriately
Two different approaches to determining E°cell
1. difference in electrode potentials between the cathode and the anode: Ecell= ecathode- eanode 2. alternatively Ecell can be thought of as the sum of the reduction potential of the reaction in the cathode and the oxidation potential of the reaction in the anode:𝐄𝐜𝐞𝐥𝐥= 𝐄𝐫𝐞𝐝+𝐄𝐨𝐱
steps of writing the formula of a complex ion from the name
1. list the metal first 2. list neutral ligands. if more than one type list alphabetically based on chemical symbol 3. list negatively charged ligands
Rules for assigning oxidation numbers
1. the sum of oxidation numbers for each atom or ion in a compound must equal the overall charge of the compound 2. Assign oxidation numbers of +1 to Group 1A metal cations and +2 to Group 2A metal cations 3. Assign fluorine an oxidation number of -1 4. Assign hydrogen an oxidation number of +1 unless otherwise dictated by previous rules 5. Assign oxygen an oxidation number of -2 unless otherwise dictated by previous rules 6. Assign Group 7A nonmetals (Cl, Br, I) oxidation numbers of -1 unless otherwise dictated by previous rules 7. Assign Group 6A nonmetals (S, Se, Te) oxidation numbers of -2 unless otherwise dictated by previous rules 8. Assign Group 5A nonmetals (P, As, Sb) oxidation numbers of -3 unless otherwise dictated by previous rules
Methods to calculate ΔG°rxn
1. using gibs equation 2. using standard free energies of formation (ΔGf°) 3. using Hess's law
Dont forget rules of using pH to find [OH] or [H]
14-pH then 10^-that for [OH], or for just pH 10^-pH
Voltage
1V=1J/C cell potential is a measure of a redox reaction's spontaneity • when Ecell = (+) the reaction is spontaneous in the forward direction • when Ecell = (-) the forward reaction is nonspontaneous (reverse reaction is spontaneous)
octahedral structures and optical isomerism
2 bidentate and 2 monodentate or 3 sets of 2 will be superimposable and not form optical isomers
Iron pipelines sometimes have blocks of Magnesium attached to them. The purpose of the magnesium is ______ A. to serve as a sacrificial cathode. B. to block the oxygen from access to the iron. C. to block water from access to the iron. D. to aid in detecting where corosion has occurred. E. to serve as a sacrificial anode.
A. False. Magnesium behaves as an anode. B. False. It's not a coating of magnesium. It's a piece of Mg, connected by a wire. This can't block anything. C. False. It's not a coating of magnesium. It's a piece of Mg, connected by a wire. This can't block anything. D. False. This is not the purpose of the magnesium. The purpose of the magnesium is to act as a sacrificial anode, i.e., to prevent the iron from oxidizing (rusting). E. True. Magnesium has a higher oxidation potential than iron. Hence, it acts as a sacrificial anode.
Oxidizing agent
Accepts electrons and becomes reduced.
The effect of pH on Solubility
Adding H30+ will decrease solubility. The solubility of a sparingly soluble compound containing a strongly basic anion or a weakly basic anion increases with increasing acidity. This is because the added H+ will bind to the anion causing the equation to shift more to the right, increasing solubility
CHAPTER 18
CHAPTER 18
CHAPTER 19
CHAPTER 19
CHAPTER 20
CHAPTER 20
CHAPTER 23
CHAPTER 23
In the compound Na[FeCl2(C2O4)(NH3)(CO)], which of the following is a lewis base, lewis acid, or a counter ion
Cl- is acting as a Lewis base. Fe3+ is acting as a Lewis acid. NH3 is acting as a Lewis base. Na+ is acting as a counterion. CO is acting as a Lewis base.
reducing agent
Donates electrons and becomes oxidized.
comparing Ecell and E°cell
Ecell is < E°cell when Q > 1, which means when the numerator is > the denominator and the reaction goes to the left
Relating equilibrium constant (K) to cell potential
Ecell=(0.0592V/n)log K
Reduction
Gain of electrons
Which of the following ligands are potentially capable of linkage isomerism? SCN- N3- NO2- NH2CH2CH2NH2 CN-
Linkage isomers differ in the donor atoms through which the ligands are bonded. SCN-can bond either with the S or the N electron pairs, so is capable of linkage isomerism. N3-can bond with either N terminal atom. However, this leads to the same structure, so N3- is not capable of linkage isomerism. NO2- can bond with either O terminal atom or the nitrogen atom, so it is capable of linkage isomerism. This is different then N3- because one of the NO bonds is double and the other is single. Ethylene diamine (NH2CH2CH2NH2) can bond with either or both N terminal atoms. However, this leads to the same structure, so ethylene diamine is not capable of linkage isomerism. CN- can bond either with the C or the N electron pairs, so is capable of linkage isomerism.
Oxidation
Loss of electrons
naming NO2 vs ONO
NO2: nitrito ONO: nitro
concentration and nonstandard cell potential
Nernst equation • when Q = 1, all species are at standard conditions and Ecell = E°cell • when Q < 1, Ecell > E°cell • when Q > 1, Ecell < E°cell • when Q = K, reaction is at equilibrium and Ecell = 0V
18. Which of the following compounds would have the greatest molar solubility? A. AgCl (Ksp = 1.8 x 10-10) B. AgBr (Ksp = 5.0 x 10-13) C. PbCO3 (Ksp = 7.4 x 10-14) D. BaSO4 (Ksp = 1.1 x 10-10) E. Ag2CrO4 (Ksp = 2.4 x 10-12)
The AgCl, AgBr, PbCO3, BaSO4 all have the same molar ratio of ions, that is, 1:1. Hence, the most soluble of these would be the one with the largest Ksp, which is AgCl. Now we just need to quantitatively compare AgCl to Ag2CrO4 you get [X] = 1.34x10-5 = solubility of AgCl and [X] = 8.44x10-5 = solubility of Ag2CrO4 so Ag2CrO4 has the greatest molar solubility
The second law of thermodynamics
The entropy of the universe must always either increase or remain the same. It can never decrease. For any spontaneous process the entropy of the universe increases.
tetrahedral structures and optical isomerism
The mirror images of tetrahedral structures having four different functional groups attached to the central atom are not superimposable. However, the mirror images of a tetrahedral structure, which has only two types of functional groups, are superimposable.
Complex-Ion Equilibria problems
This is going to give a quadratic equation. Since K is large, we won't be able to get around the quadratic equation by using the small K rule. Hence, use the large K rule. Bring the reaction to completion, and then back to equilibrium. This means you need to find the limiting reactant
"When solid barium fluoride, BaF2, is placed in enough water to make 2.0 L of solution, it is found that 0.015 moles of BaF2 dissolve before equilibrium is reached. Calculate Ksp for BaF2.
This tells you that the value of X for the change column is (.015mol/2l)= .0075M
The diagonal rule
Under standard - state condition, any species on the left of a given half-cell reaction will react spontaneously with a species that appear on the-right of any half-cell reaction located below it, diagonal rule In periodic table, upper right is easily reduced; lower left is easily oxidized. This provides a spontaneous reaction
Dissolving metals in acid
a metal will dissolve in acid (like HCl) when the potential for the reduction of H+(aq) to H2 (g) is greater than the reduction potential of the metal's cation
complex ion
a polyatomic molecule in which a central cation is bonded to electron pair donors called ligands. The central cation acts as a lewis acid (lone pair excerptor) and bonds with lewis base(s) (lone pair donor)
Selective Precipitation
a process involving the addition of a reagent to a solution that forms a precipitate with one of the dissolved ions but not the others
Non-spontaneous process
a process that needs ongoing outside intervention to occur.
microstate
a snapshot of a macrostate that gives the exact internal energy distribution of all components at a specific instance in time. the more possible microstates available in a system, the more entropy the system has.
amphoteric
a substance that can act as both an acid and a base. some metal hydroxides can also act as lewis acids under basic conditions. They usually contain transition metals.
concentration cell
a voltaic cell that employs the same half-reaction within the anode and cathode • a difference in concentration between the half-cells drives spontaneous electron flow from the anode to the cathode • anode is the half-cell with the lower concentration • cathode is the half-cell with the higher concentration • electron flow continues until the concentrations within both halfcells become equal • concentration within the anode increases and concentration within the cathode decreases • because the same half-reaction is used for both half-cells, 𝐄𝐜𝐞𝐥𝐥= 0V
determining spontaneity using change in free energy (ΔG)
all variables are now from the systems POV note that ΔG= -T(ΔSuniv) - when ΔG<0, process is spontaneous -when ΔG>0, the process is nonspontaneous -when ΔG=0 process is at equilibrium
dissociation stoichiometry: 2 ions
S= √(Ksp)
dissociation stoichiometry: 3 ions
S= ∛(Ksp/4)
summary of structural isomers
Structural isomers-Different bonding (i.e., which atom attached to which) - Coordination isomers > e.g., [MX+]Y-and [MY+]X- (switch of ligand and counterion) - Linkage isomers >M-N-O and M-O-N-O I O (different points of attachment of the ligands to the metal ion)
Entropy: allotropes
allotropes are when you have different structures of a given elements in the same state of matter. based on the arrangements determines entropy. Dimond has less entropy than graphite because its carbon atoms are more ordered and constrained by network covalent bonds. in graphite the carbon atoms are not as tightly bound.
Voltaic/Galvanic cell
an apparatuses that produces an electrical current from a spontaneous redox reaction. electron transfer between reducing agent and oxidizing agent occurs indirectly through a wire connecting the two half-cells electrons will spontaneously flow from the electrode of greater potential energy to the electrode of lower potential energy
Entropy: molecular comlexity
at a particular temp, physical state, and molar mass, a more complex molecule has greater entropy that a less complex molecule. A more complex molecule can have its energy dispersed in more ways then a less complex molecule.
Entropy: physical state
at a particular temp, the gas state has a larger entropy than the liquid state and the liquid state has a larger entropy than the solid state. dissolved solids generally have larger entropy, compared to the undissolved version, because particles can be distributed throughout the mixture. (S°aq > S°s)
linkage isomers
based on which atom of a ligand forms a bond with the central metal cation. ONO: nitrito NO2: nitro
stereoisomers: geometric isomers
bonds have different spatial arrangement about some fixed structural features.
breaking bonds vs forming bonds
breaking bonds: endothermic forming bonds: exothermic
Sparingly soluble ionic compounds
can dissolve in water to some extent. it occurs as a equilibrium process. The extent of dissolution can be quantified by an equilibrium constant
Which of the following compounds are more soluble in acid than in pure water? X. CaCO3 Y. Fe(OH)3 Z. AgCl
combine the anion with H3O and see if it reacts. if it does it is more soluble then it would be in pure water. mixing the conjugate base of a strong acid with H3O will lead to no reaction.
naming entire coordination compound
combine the name of the complex ion(s) with the name of the counterions. name counterions as you would for simple ionic compounds
Coordination compound
compound composed of complex ion and counter ions sufficient to give no net charge. counter ions balance the charge but are not covalently bonded. the formula for the complex ion is enclosed in brackets. the counter ions are always outside the bracket
Electrodes
conductive surfaces through which the electrons enter and leave the half-cells through an attached wire
Latin names for naming negative complex ions
copper- cuprate gold- aurate iron- ferrate lead- plumbate silver- argentate tin- stannate dont forget to ONLY use these names when naming a complex anion
half cell
each half cell is a place where either oxidation or reduction occur
What does spontaneity depend on
enthalpy (H): many exothermic (-) reactions are viewed as spontaneous. Entropy (S): it is a measurement of the disorder or randomness of a system.
Predicting entropy changes (ΔS) for phase transitions
entropy of a sample of matter increases as it changes from solid to liquid to gas. Gas has more ways of arranging its particles and dispersing its energy than either liquid or solid.
Standard state of a substance
for a gas: the pure gas at a pressure of exactly 1 atm for a liquid or solid: the pure substance in its most stable form at a pressure of 1 atm and the temperature of interest for a substance in solution: concentration of exactly 1M
steps for balancing a Redox Reaction under basic conditions
if balancing under basic conditions, add enough OH-s to the side of the equation with H+s to neutralize them into water. To keep the equation balanced, add the same # of OH-s to the opposite side. Re-cancel the appropriate number of H2Os
Reversible processes
if one process is spontaneous, the opposite process must be nonspontaneous and vise vera
given a list of reactions, which have ΔS>0
if you go up in mol number, ΔS>0, and vise-vera for if you go down. Increasing the temperature results in an increase in rotational, vibrational and translational energy. Therefore, ΔS > 0. going in the direction of solid-liquid-gas results in an increase of entropy. ΔS > 0.
What does ΔG being negative represent?
if ΔG is negative the change in free energy for a reaction theoretically represents the maximum amount of energy available to do work. In real reactions the amount of energy to do work is less than ΔG due to the loss of heat to the surroundings.
What does ΔG being positive represent?
if ΔG is positive, the change in free energy represents the minimum amount of energy required for a reaction to occur.
Under what conditions could a reaction with ∆S<0 be spontaneous?
if ∆H<0 -- ∆G = ∆H - T∆S If ∆S is negative (T is always positive), then -T∆S would be positive. The only way that ∆G could be negative would be if ∆H is negative enough to overcome the positive -T∆S term. Hence, ∆H must be < 0.
Which way will electrons flow in a voltaic cell?
in a voltaic cell, electrons will flow spontaneously from the electrode with the lower E° to the electrode with the higher E°
Entropy: molar mass
in general the larger the molar mass the greater the entropy.
what does E° values indicate
indicate the potentials of the half reactions to go in the direction of reduction • half-reactions with higher E° values have a greater tendency to undergo reduction than those with lower E° values
complex ion
ion composed of a central metal cation bonded to one or more ligands (i.e. lewis bases. some metal cations can act as lewis acids (electron excepter) and form complex ions with lewis bases (electron donor)
chelating ligand
is a polydentate ligand and has the non-bonding electron pairs far enough apart, so it can form a ring. A chelating ligand must have at least two non-bonding electron pairs for two attachments to the metal cation. Oxalate (-OOCOO-) ion is well known for forming a chelate. It is bidentate, and can form a stable five membered ring.
Spontaneity: Entropy (S)
it is a thermodynamic function that is related to the spreading out f energy within a system. greater dispersal=greater energy in system=more entropy. entropy is related to the number of energetically equivalent ways to arrange components of a system (microstates) to archive a particular macrostate.
square planar structures and optical isomerism
it is impossible to have have nonsuperimposable mirror images with square planar structures; therefore, impossible to have square planar optical isomers (enantiomers).
naming and numbering negatively charged ligands anion name ending in 'ate'
ligand name becomes 'ato' example: SO4^2- : sulfato, C2O4^2- : oxalato make sure to know charges
naming and numbering negatively charged ligands anion name ending in 'ite'
ligand name becomes 'ito' example: SO3^2- : sulfito, NO2- : nitrito (OR nitro)
naming and numbering negatively charged ligands anion name ending in 'ide'
ligand name becomes 'o' Example: Cl- : chloro, OH- : hydroxo, CN- : cyano
coordination isomers
ligands and counterions swap positions. coordinated ligands change places with uncoordinated (unbound) counterions
stereoisomers: geometric isomers: cis-trans
ligands have different spatial arrangement about the central metal cation cis: ligands on same side of central atom trans: ligands on opposite sides of central atom
For a spontaneous reaction, the Second Law of Thermodynamics states:
the entropy of the universe is increasing-- The Second Law of Thermodynamics says that for any spontaneous process, ∆Suniv>0.
ΔS surroundings formula
the higher the temp, the less the enthalpy impacts the surroundings entropy. releasing heat into an over vs freezer...
given two concentrations and asked which is anode and which is cathode
the lower one is anode because it is loosing electrons
When naming a complex cation
the metal is always listed at the end. example: [Co(NO2)2(en)2]NO3 is named bis(ethylenediamine)dinitrito-N-cobalt(III)nitrate also note the the Co group in a cationic complex ion is called "cobalt", not "cobaltate"; "Cobaltate" is ONLY used in an anionic complex ion. also More than one ethylenediamine is always preceded by bis, tris, tetrakis, etc, not di, tri,tetra.
The more negative the E°....
the more readily the indicated half-reaction goes in the reverse direction and undergoes oxidation
The more positive the E°....
the more readily the indicated half-reaction undergoes reduction
Dissociation stoichiometry
the number of ions formed upon dissolution BaSO4- 2 BaF2- 3 Ksp can be used directly to compare solubilities of compounds ONLY when the compounds have the same dissociation stoichiometry
coordination number
the number of ligands directly bound to the central cation of the complex ion. dictates shape of complex ion. can range from 2 to 12 but 4 and 6 and most common. It is the toal number of ligand bonds for example each (en) binds to the cation 2 times.
Which ion will precipitate out first?
the one with the smaller Ksp. You can only look at Ksp for which precipitates first if same mol ratio of ions. if not you need to find value of 's'
Ecell
the potential difference between the two half-cells in a voltaic cell. AKA voltage.
standard electrode potential
the potential of an electrode to attract/consume electrons • standard = standard state (1 atm pressure and 1 M concentrations) • by convention, standard electrode potentials are given as reduction potentials • the more positive the standard electrode potential, the greater the tendency of the electrode to draw electrons towards it for reduction to take place
Increasing solubility of a sparingly soluble solid
the solubility of a sparingly soluble compound can be increased (in relation to pure water) if the compound is added to a solution that already contains an ion that will react with one of the ions in the compound.
Macroscopic state
the state of a system defined by a given set of macroscopic conditions such as pressure, volume, and temperature.
Amperes
the unit for measuring electrical current; the abbreviation is amp.
naming and numbering neutral ligands
they are named as usual, EXCEPT for H2O (aqua), NH3 (ammine), CO (carbonyl)
when uses words like 'X amountdissolve before equilibrium'
this is referring to the value of that substance in the change column of the ICE table
when asked to determine temperature at which a reaction is at equilibrium...
this is when ΔG°=0, so set it to zero and solve for T
relating ∆G ̊ to K
∆G ̊ =0 - K=1 ∆G ̊>0 - K<1 ∆G ̊<0 - K>1
When a stable diatomic molecule spontaneously forms from its constituent atoms, what are the signs of ∆H°, ∆S°, and ∆G°?
A + A → A2 Two atoms becoming one molecule is a loss of positional freedom. Therefore, ΔS°= - Spontaneous means ΔG°= - Considering that ΔG°= ΔH°- TΔS°, and that ΔS° is negative, the only way that ΔG° could be negative would be if ΔH° is negative. Furthermore, bond formation releases energy. Therefore, the formation of one molecule from two atoms is an exothermic process (i.e., negative ∆H).
Current
A flow of electric charge.
ligands forces the reaction which way?
A ligand is a molecule that binds specifically to a receptor site of another molecule. to the right because it will bind to the cation
monodentate ligands
A ligand that binds to the metal ion via a single donor atom. It occupies one position in the coordination sphere.
Which one of the following coordination compounds will form a precipitate when treated with an aqueous solution of AgNO3? A. [Cr(NH3)6]Cl2 B. [Cr(NH3)3Cl3] C. [Cr(NH3)5Cl](NO3)2 D. Na3[Cr(CN)6] E. K3[CrCl6]
AgNO3 forms precipitates with halogen counter ions (which are weakly bound to the H2O solvent by way of an ion-dipole bond), not with halogen ligands (which are relatively tightly bound to the transition metal cation by way of a covalent bond). [Cr(NH3)6]Cl2 contains the only halogen counterion.
Electrolytic cell
An electrochemical cell that uses an external electric source to drive a nonspontaneous, unfavorable, redox reaction to proceed.
Oxidation potential
An electrode potential associated with the oxidation half-reaction. in order for something to be a sacrificial anode, and protect an element, it needs to have a higher oxidation potential than that element.
What is true for all elements at standard conditions
At standard state conditions, ∆G° and ∆H° of all elements are zero. The only time that the entropy of a substance is zero is when the temperature is at absolute zero.
isomers
Compounds with the same formula but different arrangement of atoms.
A saturated 1.00 L solution of PbI2 has [Pb2+] = 0.00152M. The solution is exposed to the atmosphere and evaporates down to 0.500 L. Assuming no change of temperature and no supersaturation, what is [Pb2+] at equilibrium in the evaporated solution?
Evaporation of water will result in precipitation of PbI2. No matter how much water evaporates, the saturated solution will always have a concentration of 0.00152M Pb2+
concentration cells
E° is always = to 0 it is a specialized form of a galvanic cell in which both electrodes are made of the same material, rather than a potential difference causing the movement of a charge it is the concentration gradient b/w the 2 solutions
what is the value of E° for: 2H + 2e -> H2
E° will always be 0V
recognizing words for E° and E
E°= standard cell potential E= measured
values at equilibrium...
E°cell=0
Coordinate covalent bond
a covalent bond in which the shared electron pair comes from only one of the atoms
What effect does hydrogen bonding in the liquid phase have on the entropy of vaporization?
Hydrogen bonding increases the entropy of vaporization.
Consider the following complexes: I. Ni(NH3)2Cl2 (square planar) II. Rh(en)3^2+ (en = H2N-CH2-CH2-NH2) III. CoCl2Br2^2- (tetrahedral) Which complexes have geometrical isomers but not optical isomers
I. Ni(NH3)2Cl2 (square planar) has geometrical cis-trans isomers, but not optical isomers. II. Rh(en)3^2+: does not have cis-trans isomerism. To have cis-trans isomerism requires the formation of a trans isomer. It is impossible to have a trans isomer with three identical bidentate ligands. This compound forms enantiomers (which are not superimposable) meaning an optical isomer. III. It is impossible for tetrahedral structures to form cis-trans isomers, but they can form enantiomers. However, for tetrahedral structures to form enantiomers they must have four different ligands. Hence, this molecule neither forms cis-trans isomers nor enantiomers.
What is the physical significance of ∆G?
IT is the maximum work that a system can do. ∆G=workmax
For a reaction in a galvanic cell both ∆H° and ∆S° are positive than....
If ∆H° is positive, and ∆S° is positive, then ΔG° will be negative when the T∆S° term is sufficiently large, i.e., ΔG° will decrease as T increases. Since ΔE° has the opposite sign of ∆G°, then ∆E° will increase as T increases.
Common Bi- and polydentate ligands
LOOK IN NOTES: must know names, charges and bond numbers
common monodentate ligands
LOOK IN NOTES: must know names, charges and bond numbers
bidentate ligands
Ligands that can donate 2 lone pairs of electrons to the central metal ion to form 2 coordinate bonds.
oxidation number
Positive or negative number that indicates how many electrons an atom has gained, lost, or shared to become stable
how do you name: K2[Fe(CN)4]
Potassium tetracyanoferrate(II) note that even though there are two potassium you still just say 'potassium', no di. you name counterions as you would for simple ionic compounds
Comparing Q to Ksp
Q>Ksp, the solution is above saturation and precipitation WILL occur Q<Ksp, the solution is unsaturation and precipitation will NOT occur Q=Ksp, the sollution is at equilibrium and saturated. Precipitation will just BEGIN to occur
What are the effects of ΔH and ΔS on spontaneity
Recall ΔG= ΔH -TΔS liquid to gas is not spontaneous at temps below 100C/boiling point
Voltaic cells vs. Electrolytic cells
Voltaic: -redox reaction➝ electrical current -anode (-) is source of electrongs -Cathode (+) draws electrons towards it -spontaneously occurs Electrolytic: -electrical current➝ nonspontaneous reaction -anode is attached to the (+) terminal of battery, electrons pulled out of anode by the battery -cathode is attached to the (-) terminal of the battery, electrons forced into the cathode by the battery Both -oxidation at the anode -reduction at the cathode -electrons flow from anode to cathode
The common ion effect
When a slightly soluble solid is dissolved in solution, and another salt with a common ion is added, equilibrium shifts left, causing precipitation
What is the relationship between ΔG° and K
WhenΔG° has a large magnitude and is negative, the value of K is relatively large-- both indicate spontaneous reaction when ΔG° has a large magnitude and is positive, the value of K is relatively small-- both indicate a nonspontaneous reaction
Consider the following two half reactions and the statements that follow: Ag+(aq) + 1 e- → Ag(s) 2 Ag+(aq) + 2 e- → 2 Ag(s) X. ΔG° is the same for both reactions Y. E° is the same for both reactions Z. Both reactions are oxidations
X. False. Gibbs free energy is an extensive property. Therefore, the value depends on the quantity. Since the second equation is double that of the first, the Gibbs free energy is double for the second reaction. Y. True. Voltage is an intensive property. Therefore, the value is unrelated to the quantity; i.e., doubling the equation doesn't change the voltage. Hence, the voltage of the second reaction is the same as the voltage of the first reaction. Z. False. Both reactions are reductions.
The solubility product, Ksp, of PbCl2 is 1.6 × 10-5. What mass of KCl(s) must be dissolved in 150.00 mL of 1.15M Pb(NO3)2 to produce a solution that is just saturated in PbCl2?
[Pb2+][Cl-]^2= Ksp 1.15 x (2X)^2= 1.6 x 10-5 X = 1.865 x 10-3 2X = 3.73 x 10-3M Cl- = 3.73 x 10-3 M KCl 3.73 x 10-3 mol/L x 0.150L = 5.595 x 10-4 mol KCl in 150.00 mL 5.595 x 10-4 mol KCl x 74.55 g/mol = 0.0417 g KCl
polydentate ligand
ligands that can fill TWO OR MORE coordination sites. This is a result of two or more atoms being able to donate a pair of electrons
The effects of temperature on the equilibrium constant
linearizer form: 2 point form:
line form... ln(K) = -∆H°/RT + ∆S°/R
ln(K) = -∆H°/RT + ∆S°/R Y-axis = ln(K) X-axis = 1/T Slope = -∆H°/R Y-intercept = ∆S°/R
optical isomerism in [Co(en)3]3+
look at notes
electroplating
metal cations are reduced at the cathode to form the nurtral metal The higher the electrical current, the more metal deposited at the cathode the longer the duration of current, the more metal deposited at the cathode
Inert electrodes
metals in each half reaction act as electrodes. if there is no metal present an inert electrode must be employed Conductors that do not react or take part in the reaction. Platinum or Graphite is an example.
Types of ligands
monodentate bidentate polydentate
molar solubility of a compound
number of moles of a compound that dissolves per liter of aqueous solution (M) is calculated usuing Ksp value Use ICE table and solve for 's'
stereoisomers: geometric isomers: fac-mer isomers
occurs in octahedral geometry where only three of the ligands are identical. fac: the ligands make up a face of the octahedron mer: the ligands lie along a meridian of the octahedron
Spontaneous process
occurs without any ongoing outside intervention
positive electrode potential
reflects a high tendency for reduction. In an electrolytic cell, negative ions move toward.
negative electrode potential
reflects a low tendency for reduction (and high tendency for oxidation).
Standard molar entropy of a substance (S°)
the energy dispersed into one mole of that substance in its standard state at a given temperature (usually 25C)
dissociation stoichiometry: 5 ions
s= 5√(Ksp/108)
dissociation stoichiometry: 4 ions
s= ∜(Ksp/27)
Stereoisomers
same formula and connectivity, but different spatial orientations of atoms -geometric isomers (cis-trans isomers and fac-mer isomers) -optical isomers
Structural isomers
same formula but diffrent order of connectivity -coordination isomers -linkage isomers
stereoisomers: optical isomers
species that are nonsuperimposable mirror images
Given a list of choices, which is the strongest reducing agent?
strong reducing agents are easily oxidized. Thestrongest reducing agents are in the lower left-hand corner of the periodic table.
Standard cell potential (E°cell)
the cell potential under standard conditions (solution at 1M and gages at partial pressure of 1 atm)
When an ideal, inert gas A is placed in a tank containing a different ideal, inert gas B, gas A spontaneously disperses throughout gas B because:
the dispersion of atoms produces an increase in entropy. Another way of explaining the spontaneous mixing of gas A and gas B is an increase in "positional freedom".
Anode
the electrode where oxidation occurs • acts as a source of electrons • designated by a negative sign (-)
Cathode
the electrode where reduction occurs • consumes the electrons formed at the anode • designated by a positive sign (+)
common ion effect forces the reaction which way?
to the left
Salt bridge
typically a U-shaped tube filled with a strong electrolyte used to prevent charge build-up and complete the circuit • as e -s flow, positive and negative charges builds-up in the anode and cathode, respectively • anions in the salt bridge migrate towards the anode • cations in the salt bridge migrate towards the cathode
ranking compounds in order of increasing solubility
use dissociation stoichiometry and Ksp to find S, molar solubility, based on number of ions. The greater the value of S the more soluble it is.
If given values and asked if precipitate form?
use given values and equation to find value of Q. compare it to Ksp and use rules above to check if it will precipitate. The reason why when Q<K it doesnt precipitate is because when Q is smaller than Ksp it means that the numerator is too small, which means that there are not enough product ions to reach K, which means that the solution is undersaturated. No precipitate will form
when does ΔG = ΔG°
when Q = 1 ΔG = ΔG°+ RT ln(Q) X = X + RT ln(Q) 0 = RT ln(Q) Q = 1
Entropy change of the surroundings
when a reaction is exothermic (ΔH(-)), the system releases its energy into the surroundings. this means ΔSsurr is (+) when a reaction is endothermic (ΔH(+)), the system absorbs energy from the surroundings. this means ΔSsurr is (-)
Precipitation
when ions in solution combine to form insoluble ionic compound, the compound precipitates out of the solution as a solid. Precipitation= 1/Ksp.... for this reason it is a very big number, so we can use a single headed arrow.
Which one of the following salts does not become more soluble, when the pH of the solution is lowered? A. ZnS B. BaF2 C. AgCl D. NiCO3 E. Al(OH)3
write out the equation of breaking apart the compounds given to its ions. make another equation mixing the anion with H3O. If the anion can mix with the H then the equation will fall further to the write, making the original compound more soluble.
Precipitation and Q
you have know concentration of two things before mixing. after mixing use M1V1=M2V2. Precipitations also begin when Q=K
Suppose 0.500 atm of H2S, O2, H2O, and SO2 are added to a 1.000L container at 25°C. Calculate ΔG for this reaction under these conditions. 2H2S(g) + 3O2(g) ⇌ 2H2O(g) + 2SO2(g) Kc = 3.0×105
ΔG = ΔG°+ RT ln(Q) At equilibrium, ΔG = 0 0 = ΔG°+RT ln(K) ΔG°= -RT ln(K) ΔG°= -8.314Jdeg-1mol-1 x 298K x (ln(3.0 x 105)) = -3.12e04J Under non-standard state conditions: ΔG = ΔG°+ RT ln(Q) Q = (([PH2O]2)([PSO2]2))/(([PH2S]2)([PO2]3)) Q = (([0.500]2)([0.500]2))/(([0.500]2)([0.500]3)) = 2.00 ΔG = (-3.12 x 104J) + ((8.314Jdeg-1mol-1) x (298K) x (ln(2.00))) = -2.95e4J = -29.5kJ
extensive and intensive
ΔG: extensive- changes with quantity E°: intensive- no change with quantity
What is the relationship between ΔG°rxn and ΔGrxn
ΔGrxn= nonstandard free energy change (kJ/mol) ΔG°rxn= standard free energy change (kJ/mol) R= .008314 kJ/molK T= temp (K) Q= reaction quotient (unitless)
If a reaction is spontaneous at all temperatures we can conclude that:
ΔH is negative and ΔS is positive. When ΔH is negative and ΔS is positive then ΔG will be negative, a requirement for a reaction to be spontaneous. (ΔG = ΔH - TΔS) ΔG will be negative (spontaneous) at all temperatures.
What happens with H2O(l)--> H2O (g) at 90C and a PH2O= 1atm?
ΔΗ: Bonds are broken in going from a liquid to a gas. Therefore, this is an endothermic reaction, ΔΗ = +. ΔS: The entropy increases in going from a liquid to a gas. Therefore, ΔS = +. ΔG: At 90°C, i.e., below the boiling point, H2O(g) → H2O(l) is spontaneous. H2O(l) → H2O(g) is notspontaneous. Therefore, ΔG = +.
Standard hydrogen electrode (SHE)
• half-reactions with a stronger tendency toward reduction than the SHE have a positive value for E°red • half-reactions with a stronger tendency toward oxidation than the SHE have a negative value for E°red • for an oxidation half-reaction, E° oxidation = −E°reduction
Free energy and cell potential
•ΔG°= standard free energy change (J) •E°cell= standard cell potential (V orJ/C) •n= number of moles of electrons transferred in the balanced redox reaction •F = Faraday's constant = 96 485 C/mol e-
given a reaction and asked in which will ∆G be > 0?
∆G would be > 0, i.e., spontaneous to the left, when Q is greater than K
