CHEM 162 EXAM 3 QUESTIONS AND
ANSWERS
How many of the following processes are nonspontaneous? climbing stairs dissolving
salt in water converting table salt to its elements 2 H₂O(l) → 2 H₂(g) + O₂(g)
A) 0
B) 1
C) 2
D) 3
E) 4 - Correct Answers -3
What must be true of a spontaneous process?
A) Enthalpy must increase.
B) There will be a flow of heat.
C) Entropy of the universe increases.
D) Entropy of the system increases.
E) Entropy of the surroundings increases. - Correct Answers -C) Entropy of the universe
increases.
What will the sign on ∆S be for the following reaction and why? 2 Mg (s) + O₂ (g) → 2
MgO (s) - Correct Answers -D) Negative, because there are more moles of gas on the
reactant side than the product side.
Which of the following processes has a negative ∆S?
A) CaCO₃(s) → CaO(s) + CO₂(g)
B) H₂O(g) → H₂O(s)
C) CO₂(s) → CO₂(g)
D) C₆H₁₂O₆(s) → C₆H₁₂O₆(aq)
E) ∆S cannot be negative - Correct Answers -B) H₂O(g) → H₂O(s)
If the Gibbs free energy for an equilibrium is a large, negative number, the equilibrium
constant is expected to be _____
A) a large, negative value
B) a large, positive value
C) a small, negative value
D) a small, positive value
E) Zero - Correct Answers -B) a large, positive value
, An unknown acid, HB, has a ∆G°rxn of 27.5 kJ/mol at 298 K. What is the pKa of HB? -
Correct Answers -4.820
For cyclohexane, the ∆H° of vaporization is 33.10 kJ/mol and the ∆S° of vaporization is
111.80 J/mol･K. At 1.00 atm, what is the boiling point of cyclohexane, in K? - Correct
Answers -296.1 K
Which of the following reactions would have the most positive ∆S° value?
A) SO₂(g) + Na₂O(s) ⟶ Na₂SO₃(s)
B) CO₂(s) ⟶ CO₂(g)
C) Fe³⁺(aq) + SCN⁻(aq) ⟶ FeSCN²⁺(aq)
D) N₂(g) + 3 H₂(g) ⟶ 2 NH₃(g)
E) 2 NO(g) + Cl₂(g) ⟶ 2 NOCl(g) - Correct Answers -B) CO₂(s) ⟶ CO₂(g)
A reaction which is endothermic and has an overall increase in entropy is
A) spontaneous only at high T
B) spontaneous only at low T
C) always spontaneous as written.
D) always spontaneous in the reverse direction. - Correct Answers -A) spontaneous
only at high T
A reaction which is exothermic and has an overall increase in entropy is
A) spontaneous only at high T
B) spontaneous only at low T
C) always spontaneous
D) spontaneous in the reverse direction. - Correct Answers -C) always spontaneous
A reaction will be spontaneous at all temperatures if _____
A) ∆H and ∆S are positive
B) ∆H and ∆S are negative
C) ∆H is positive and ∆S is negative
D) ∆H is negative and ∆S is positive - Correct Answers -D) ∆H is negative and ∆S is
positive
Which of the following pairs of substances has the species with the higher entropy listed
first?
A) Na(s), Na(l)
B) Mg(NO₃)₂(s), Mg(NO₃)₂(aq)
C) Ca(s), UF₆(g)
D) Ni(s), Br₂(l)
E) Ar(g), Hg(l) - Correct Answers -E) Ar(g), Hg(l)
in general gases have higher entropy than solids.
Which of the following is true for a perfect crystal at absolute zero? - Correct Answers -
C) S = 0
ANSWERS
How many of the following processes are nonspontaneous? climbing stairs dissolving
salt in water converting table salt to its elements 2 H₂O(l) → 2 H₂(g) + O₂(g)
A) 0
B) 1
C) 2
D) 3
E) 4 - Correct Answers -3
What must be true of a spontaneous process?
A) Enthalpy must increase.
B) There will be a flow of heat.
C) Entropy of the universe increases.
D) Entropy of the system increases.
E) Entropy of the surroundings increases. - Correct Answers -C) Entropy of the universe
increases.
What will the sign on ∆S be for the following reaction and why? 2 Mg (s) + O₂ (g) → 2
MgO (s) - Correct Answers -D) Negative, because there are more moles of gas on the
reactant side than the product side.
Which of the following processes has a negative ∆S?
A) CaCO₃(s) → CaO(s) + CO₂(g)
B) H₂O(g) → H₂O(s)
C) CO₂(s) → CO₂(g)
D) C₆H₁₂O₆(s) → C₆H₁₂O₆(aq)
E) ∆S cannot be negative - Correct Answers -B) H₂O(g) → H₂O(s)
If the Gibbs free energy for an equilibrium is a large, negative number, the equilibrium
constant is expected to be _____
A) a large, negative value
B) a large, positive value
C) a small, negative value
D) a small, positive value
E) Zero - Correct Answers -B) a large, positive value
, An unknown acid, HB, has a ∆G°rxn of 27.5 kJ/mol at 298 K. What is the pKa of HB? -
Correct Answers -4.820
For cyclohexane, the ∆H° of vaporization is 33.10 kJ/mol and the ∆S° of vaporization is
111.80 J/mol･K. At 1.00 atm, what is the boiling point of cyclohexane, in K? - Correct
Answers -296.1 K
Which of the following reactions would have the most positive ∆S° value?
A) SO₂(g) + Na₂O(s) ⟶ Na₂SO₃(s)
B) CO₂(s) ⟶ CO₂(g)
C) Fe³⁺(aq) + SCN⁻(aq) ⟶ FeSCN²⁺(aq)
D) N₂(g) + 3 H₂(g) ⟶ 2 NH₃(g)
E) 2 NO(g) + Cl₂(g) ⟶ 2 NOCl(g) - Correct Answers -B) CO₂(s) ⟶ CO₂(g)
A reaction which is endothermic and has an overall increase in entropy is
A) spontaneous only at high T
B) spontaneous only at low T
C) always spontaneous as written.
D) always spontaneous in the reverse direction. - Correct Answers -A) spontaneous
only at high T
A reaction which is exothermic and has an overall increase in entropy is
A) spontaneous only at high T
B) spontaneous only at low T
C) always spontaneous
D) spontaneous in the reverse direction. - Correct Answers -C) always spontaneous
A reaction will be spontaneous at all temperatures if _____
A) ∆H and ∆S are positive
B) ∆H and ∆S are negative
C) ∆H is positive and ∆S is negative
D) ∆H is negative and ∆S is positive - Correct Answers -D) ∆H is negative and ∆S is
positive
Which of the following pairs of substances has the species with the higher entropy listed
first?
A) Na(s), Na(l)
B) Mg(NO₃)₂(s), Mg(NO₃)₂(aq)
C) Ca(s), UF₆(g)
D) Ni(s), Br₂(l)
E) Ar(g), Hg(l) - Correct Answers -E) Ar(g), Hg(l)
in general gases have higher entropy than solids.
Which of the following is true for a perfect crystal at absolute zero? - Correct Answers -
C) S = 0
