AP Chemistry Review Questions - Spontaneity, Entropy, and Free Energy

For which of the following processes would ΔS° be expected to be most positive?
1. CO₂(g) → CO₂(s)
2. C₆H₁₂O₆(s) + 6 O₂(g) → 6 CO₂(g) + 6 H₂0(g)
3. Na⁺(aq) + Cl^-(aq) → NaCl(s)
4. H⁺(aq) + OH^-(aq) → H₂O(l)
5. Cl₂(g) + H₂(g) → 2 HCl(g)
Which of the following statements is true?
1. Exothermic reactions are always spontaneous
2. For a process to be spontaneous, the number of moles of product must exceed the number of moles of reactant
3. The entropy of the universe is increasing
4. A system at constant temperature cannot experience entropy changes
5. In a spontaneous process, DG has a positive value
Which of the following samples of oxygen has the greatest positional entropy?
1. 1 mole of O₂(g) at 1.0 atm and 273 K
2. 1 mole of O₂(g) at 0.5 atm and 273 K
3. 1 mole of O₂(g) at 2.0 atm and 273 K
4. 1 mole of O₂(s) at 15 K
5. 1 mole of O₂(g) at 2.0 atm and 200 K
It is determined that for a particular process, ΔH = +185 kJ and ΔS = +1.80 J/K. At what temperature does the reaction become spontaneous?
1. 333 K
2. 1.03 x 10⁵ K
3. 0.00973 K
4. 187 K
5. 376
The boiling point of compound X is 12.0°C, and the enthalpy of vaporization of compound X is 24.6 kJ/mol. What is the entropy of vaporization for compound X?
1. 295 J/(K·mol)
2. 11.6 J/(K·mol)
3. 0.0863 J/(K·mol)
4. 2.05 J/(K·mol)
5. 86.3 J/(K·mol)
A two bulbed flask contains four particles. What is the probability of finding all four particles in only one of the bulbs?
1. 6.25 %
2. 25 %
3. 11.3 %
4. 0 %
5. 0.0625 %
Which of these processes occurs with a decrease in entropy?
1. decomposition of liquid water
2. rusting of iron
3. combustion of methane
4. oxidation of glucose
5. melting of ice
Calculate ΔS° for the following reaction:
2 NH₃ → 3 H₂ + N₂.
Substance Sº J/(K mol)
NH₃(g)
193
H₂(g)
131
N₂(g)
192
1. -212 J/K
2. 130 J/K
3. 971 J/K
4. 199 J/K
5. -54 J/K
The lowest possible entropy achievable occurs:
1. only at very high temperatures
2. only in the vapor phase
3. when a liquid is converted to a solid
4. in a perfect crystal at 0 K
5. at the completion of an endothermic reaction
Which of the following statements are true for the reaction I₂(g) → 2 I(g)

I. ΔH is positive
II. ΔH is negative
III. ΔS is positive
IV. ΔS is negative
V. The reaction is spontaneous at any temperature
1. I only
2. I and III
3. II and IV
4. V only
5. IV only
The standard free energy of formation of NaBr(s) is -347 kJ/mol. Calculate ΔG° for the reaction

2NaBr(s) → 2Na(s) + Br₂(l)
1. -347 kJ
2. 347 kJ
3. 694 kJ
4. -694 kJ
5. -112 kJ
Which of the following liquids is likely to have the highest value for S°?
1. H₂O
2. C₂H₅OH
3. CH₃OH
4. N₂H₄
5. Hg
At 25°, the free energy of formation of gaseous water is -229 kJ/mol. Calculate ΔG for the following reaction if the hydrogen is supplied at 4.00 atm and the oxygen is supplied at 3.00 atm, while the water produced is at 1.00 atm pressure.
2H₂ + O₂ → 2H₂O
1. -239 kJ
2. -568 kJ
3. -10148 kJ
4. -9819 kJ
5. 453 kJ
Determine ΔG° for the weak acid HC₂H₃O₂ (acetic acid, K_a = 1.8 x 10^-5) at 25°C.
1. 27 kJ/mol
2. 14.1 kJ/mol
3. 356 kJ/mol
4. -11 kJ/mol
5. 211 kJ/mol

Substance	Sº J/(K mol)
NH₃(g)	193
H₂(g)	131
N₂(g)	192