Chapter 18 Practice
MULTIPLE CHOICE. Choose the one alternative that best completes the statement or answers the question.
1) A reaction that is spontaneous as written ________.
A) is also spontaneous in the reverse direction
B) is very rapid
C) is very slow
D) will proceed without outside intervention
E) has an equilibrium position that lies far to the left
1)
2) The entropy of the universe is ________.
A) zero
B) continually decreasing
C) the same as the energy, E
D) constant
E) continually increasing
2)
3) S is positive for the reaction ________.
A) 2N2 (g) + 3H2 (g) → 2NH 3 (g)
3)
B) C2H4 (g) + H2 (g) → C2H6 (g)
C) Mg (s) + Cl2 (g) → MgCl2 (s)
D) 2NO (g) + O2 (g) → 2NO2 (g)
E) C3H8 (g) + 5 O2 (g) → 3CO2 (g) + 4 H2O (g)
4) Which reaction produces a decrease in the entropy of the system?
A) Na (s) + 1/2 Cl 2 (g) → NaCl (s)
4)
B) 2 HgO (s) → 2 Hg (l) + O2 (g)
C) H2O (s) → H2O (g)
D) 4 NH3 (g) + 5 O2 (g) → 4 NO (g) + 6 H2O (g)
E) UF6 (s) → U (s) + 3F 2 (g)
5) Consider the reaction:
5)
Ag+ (aq) + Cl- (aq) → AgCl (s)
Given the following table of thermodynamic data,
Substance
Ag+ (aq)
Cl- (aq)
AgCl (s)
Hf° (kJ/mol) S° (J/mol ∙ K)
105.90
-167.2
-127.0
73.93
56.5
96.11
determine the temperature (in °C) above which the reaction is nonspontaneous under standard
conditions.
A) 432
B) 133
C) 1230
D) 1640
E) 150
A-1
6) Calculate △ S°rxn for the following reaction. The S° for each species is shown below the
6)
reaction.
S°(J/mol∙K)
P4(g) + 10 Cl2(g) → 4 PCl 5(g)
280.0
223.1
364.6
A) +171.3 J/K
B) -583.6 J/K
C) +307.7 J/K
D) -1052.6 J/K
E) +138.5 J/K
7) Which one of the following statements is true about the equilibrium constant for a reaction if
G° for the reaction is negative?
A) K > 1
B) K = 1
C) K = 0
D) K < 1
E) More information is needed.
7)
8) The standard Gibbs free energy of formation of ________ is zero.
8)
(a) H2O (l)
(b) O (g)
(c) Cl2 (g)
A) (a) only
B) (b) only
C) (c) only
D) (b) and (c)
E) (a), (b), and (c)
9) For a reaction to be spontaneous at low temperature, the signs of H° and S° must be ________
and ________, respectively.
A) –, +
B) –, –
C) +, 0
D) +, +
E) +, –
9)
10) Determine G°rxn using the following information.
10)
H2(g) + CO(g) → CH2O(g)
A) +41.5 kJ
B) +34.6 kJ
H°= +1.9 kJ;
C) -17.3 kJ
A-2
S°= -109.6 J/K
D) +30.8 kJ
E) +57.7 kJ
11) Calculate the G°rxn using the following information.
11)
4 HNO3(g) + 5 N2H4(l) → 7 N2(g) + 12 H2O(l)
G° f (kJ/mol)
-73.5
149.3
G° rxn = ?
-237.1
A) +110.7 kJ
B) -3.298 × 10 3 kJ
C) +3.298 × 10 3 kJ
D) -954.7 kJ
E) -312.9 kJ
12) Which of the following is NOT true for Grxn?
A) If G°rxn > 0, the reaction is spontaneous in the forward direction.
12)
B) Under equilibrium conditions, Grxn = 0.
C) If Q = 1, then DGrxn = G°rxn.
D) If G°rxn > 0, the reaction is spontaneous in the reverse direction.
E) If G°rxn < 0, the reaction is spontaneous in the forward direction.
13) Determine the equilibrium constant for the following reaction at 298 K.
Cl(g) + O3(g) → ClO(g) + O2(g)
13)
G° = - 34.5 kJ
A) 0.986
B) 5.66 × 10 5
C) 4.98 × 10 -4
D) 8.96 × 10 -7
E) 1.12 × 10 6
14) For a given reaction, H = -27.7 kJ/mol and S = -76.6 J/Kmol. The reaction will have G = 0
at _________ K. Assume that H and S do not vary with temperature.
A) 298
B) 2765
C) 362
D) 0.362
E) 2.77
14)
15) Calculate the G°rxn using the following information at 298K..
15)
2 HNO3(aq) + NO(g) → 3 NO 2(g) + H2O(l)
H°f (kJ/mol)
S°(J/mol∙K)
A) +85.5 kJ
-207.0
91.3
33.2
-285.8
146.0
210.8
240.1
70.0
B) +50.8 kJ
C) +186 kJ
G° rxn = ?
D) -222 kJ
E) -151 kJ
16) Calculate Grxn at 298 K under the conditions shown below for the following reaction.
SO3(g) + H2O(g) → H2SO4(l)
G°= -90.5 kJ
P(SO3) = 0.20 atm, P(H2O) = 0.88 atm
A) -86.8 kJ
B) -94.2 kJ
C) +94.2 kJ
A-3
D) -86.2 kJ
E) +86.8 kJ
16)
17) Calculate Grxn at 308 K under the conditions shown below for the following reaction.
Fe2O3(s) + 3 CO(g) → 2 Fe(s) + 3 CO2(g)
17)
G° = -28.0 kJ
P(CO) = 1.4 atm, P(CO2) = 2.1 atm
A) -24.9 kJ
B) -31.1 kJ
C) +24.9 kJ
D) +30.0 kJ
E) +31.1 kJ
18) Use the free energies of formation given below to calculate the equilibrium constant (K) for the
following reaction at 298 K.
2 HNO3(aq) + NO(g) → 3 NO 2(g) + H2O(l)
G° f (kJ/mol) -110.9
87.6
51.3
18)
K=?
-237.1
A) 8.71 × 10 8
B) 1.15 × 10 -9
C) 1.02
D) 0.980
E) 5.11 × 10 -4
19) Which of the three laws of thermodynamics states the criterion for spontaneity?
A) the second law of thermodynamics
B) both the second and third laws of thermodynamics
C) the third law of thermodynamics
D) the first law of thermodynamics
19)
SHORT ANSWER. Write the word or phrase that best completes each statement or answers the question.
20) Consider the following reaction
2 SO 2 + O2 ⇌ 2 SO3
20)
∆H˚ = -180 kJ/mol
K is measured to be 9.9×102 at 800 K, what temperature would the reaction need to be
run at to get an equilibrium constant of 1×10 6?
A-4
21) Given the following van't Hoff plot,
a) is the ∆S˚ positive or negative?
b) is the ∆H˚ positive or negative?
21)
22) Given the following: ∆S˚ = –30J/mol, ∆H˚ = –8.0 kJ/mol. At T = 200 K, find the K.
22)
A-5
Answer Key
Testname: CHAPTER 19 PRACTICE
1) D
2) E
3) E
4) A
5) D
6) D
7) A
8) C
9) B
10) B
11) B
12) A
13) E
14) C
15) B
16) D
17) A
18) B
19) A
20) 637.15 K
21) ∆S˚ = +; ∆H˚ = +
22) 3.33 (if you use 200 ˚C, K = 0.207)
A-6