Chem 152 Final Exam Review

Reaction Shift based on Q and K

1. Q < K = Shifts right

2. Q > K = Shifts left

3. Q = K = Equilibrium

What way does rxn shift if K is extremely large or small?

1. K is extremely large = Shifts right

2. K is extremely small = Shifts left

Le Chatelier’s Principle

1. Add reactant = Shift right

2. Add product = Shift left

3. Remove product = Shift right

4. Remove reactant = Shift left

Shifts with pressure/volume

1. Increase pressure = Shifts towards fewer gas moles

2. Decrease pressure = Shifts towards more gas moles

Shifts with Temp (Endo vs Exo)

1. Endothermic = Shifts right

2. Exothermic = Shifts left

Who accepts protons and who donates them?

Acid = Proton donor

Base = Proton acceptor

pH Relationship

pH + pOH = 14

Water Autoionization

Kw = [H+][OH-] = 1.0×10^-14

Relationship between Ka and Kb

Ka * Kb = Kw

What always makes a buffer?

weak acid + weak base

Can buffers have a strong base or strong acid?

Only if the strong thing (acid or base) is limiting

How are moles acid and moles base related at equivalence point in titrations?

moles acid = moles base

What happens at the midpoint on a titration graph:

At the midpoint, which is half of the equivalence point, pH = pKa

How to do titration problems for a strong acid/strong base?

1. Calculate the moles of the excess reactant

2. Divide by total volume

3. Calculate pH/pOH

What is left at the equivalence point?

Only the base is left, so:

1. Divide moles by total volume

2. ICE table

3. Find pH or pOH

When does a precipitate form?

1. Q > Ksp = Precipitate forms

2. Q < Ksp = No Precipitate

How does common ions affect solubility?

Common ions decrease solubility

When does entropy increase?

• solid → liquid

• liquid → gas

• more gas molecules

• larger volume

Relationship between Gibbs free energy and spontaneity

1. ΔG > 0 = Reverse rxn is spontaneous

2. ΔG < 0 = Spontaneous

3. ΔG = 0 = Equilibrium

Relationship between Gibbs free energy and equilibrium constant

If K > 1, then ΔG is negative

Relationship between redox half reactions and anodes and cathodes

Anode = Oxidation

Cathode = Reduction

Relationship between E∘ and spontaneity

If E∘ is positive, then spontaneous

Relationship between Nernst equation and Q

As Q increase, E decreases

Relationship between entropy and spontaneity

1. ΔSuniv > 0 = Spontaneous

2. ΔSuniv < 0 = Nonspontaneous

3. ΔSuniv = 0 = Equilibrium

Relationship between entropy of the surroundings and heat

1. If reaction releases heat → surroundings entropy increases

2. If reaction absorbs heat → surroundings entropy decreases

Difference between entropy and enthalpy

• enthalpy = energy change

• entropy = disorder change

• temperature determines which dominates

Relationship between entropy + enthalpy and spontaneity

1. ΔS < 0 and ΔH < 0 = Spontaneous at LOW temps

2. ΔS > 0 and ΔH > 0 = Spontaneous at HIGH temps

3. ΔS > 0 and ΔH < 0 = Spontaneous ALWAYS

4. ΔS < 0 and ΔH > 0 = Spontaneous NEVER

Relationship between temperature and enthalpy

1. If ΔH > 0 (endothermic) = increase T → shift right

2. If ΔH < 0 (exothermic) = increase T → shift left

Relationship between Ksp and solubility

Directly proportional

Relationship between Ka/pH and Kb/pH

Ka/pH is INVERSE and Kb/pH is DIRECT

What does pH/pOH tell us?

pH/pOH tells us about concentrations, NOT acid/base strength

What is Isobaric vs Isocaric?

Isobaric = Constant Pressure

Isocaric = Constant Volume