A)
+ + +
B)
+ – –
C)
– + +
D)
– – +
E)
– – –
Consider the reaction
2N2O5(g) 4NO2(g) + O2(g)
at 25°C for which the following data are relevant:
Hf°
S°
N2O5
11.289 kJ/mol
355.32 J/K mol
NO2
33.150 kJ/mol
239.90 J/K mol
O2
0 kJ/mol
204.80 J/K mol
69. Calculate S° for the reaction.
A)
809.08 J/K
B)
89.38 J/K
C)
453.76 J/K
D)
–265.94 J/K
E)
1164.40 J/K
70. Calculate H° for the reaction.
A)
110.022 kJ
B)
10.572 kJ
C)
121.311 kJ
D)
21.861 kJ
E)
155.178 kJ
71. Calculate G° for the reaction at 25°C.
A)
–1.35 105 kJ
B)
98.7 kJ
C)
–25.2 kJ
D)
135 kJ
E)
0
72. The reaction is allowed to proceed until all substances involved have reached their
equilibrium concentrations. Under those conditions, what is G for the reaction?
A)
–1.35 105 kJ
B)
98.7 kJ
C)
–25.2 kJ
D)
135 kJ
E)
0
73. Which of the following is true for this reaction?
A)
Both H° and S° favor the reaction’s spontaneity.
B)
Both H° and S° oppose the reaction’s spontaneity.
C)
H° favors the reaction, but S° opposes it.
D)
H° opposes the reaction, but S° favors it.
E)
The reaction cannot occur at room temperature.
74. Which of the following is not a state function?
A)
q
B)
G
C)
H
D)
E
E)
P
75. The standard free energy of formation of KCl(s) is –408.8 kJ/mol. G° for the reaction
2KCl(s) → 2K(s) + Cl2(g) is:
A)
–408.8 kJ
B)
817.6 kJ
C)
408.8 kJ
D)
–817.6 kJ
E)
none of these
76. Consider the following hypothetical reaction at 310 K. Standard free energies of formation
are given in parentheses.
B
→
G° = –32.6 kJ/mol
(?)
(176.4
kJ/mol)
Calculate the standard free energy of formation of compound B.
A)
209.0 kJ/mol
B)
–209.0 kJ/mol
C)
143.8 kJ/mol
D)
–143.8 kJ/mol
E)
none of these
77. For the reaction H° = 126.4 kJ/mol and S° = –74.9 J/K
mol.
At 361°C, what is G ?
A)
153.4 kJ/mol
B)
47.6 kJ/mol
C)
173.9 kJ/mol
D)
78.9 kJ/mol
E)
155.0 kJ/mol
78. Determine G° for the following reaction:
CH4(g) + 2O2(g) → CO2(g) + 2H2O(l)
Substance
Gf°(kJ/mol)
CH4(g)
–50.69
O2(g)
0
CO2(g)
–394.4
H2O(l)
–237.4
A)
–581.1 kJ
B)
–919.9 kJ
C)
–818.5 kJ
D)
–682.5 kJ
E)
131.1 kJ
79. Of S, Ssurr, Suniv, and G, which are state functions?
A)
S, Ssurr, Suniv, and G are all state functions.
B)
Only S, Suniv, and G are state functions.
C)
Only S and G are state functions.
D)
Only S, Ssurr, and Suniv are state functions.
E)
Only Suniv and G are state functions.
80. At 699 K, G° = –23.25 kJ for the reaction H2(g) + I2(g) 2HI(g). Calculate G for this
reaction if the reagents are both supplied at 10.0 atm pressure and the product is at 1.76 atm
pressure.
A)
–20.2 kJ
B)
20.2 kJ
C)
3.1 kJ
D)
–43.4 kJ
E)
43.4 kJ
81. The standard molar free energies of formation of NO2(g) and N2O4(g) at 25°C are 51.84 and
98.00 kJ/mol, respectively. What is the value of G for the reaction written as follows at
25°C if the pressures of both gases are 1.33 atm?
2NO2 N2O4
A)
–4.97
B)
4.97
C)
–6.39
D)
–5.68
E)
–5.74
82. Elemental sulfur exists in two crystalline forms, rhombic and monoclinic. From the
following data, calculate the equilibrium temperature at which monoclinic sulfur and
rhombic sulfur are in equilibrium.
Hf° (kJ/mol)
S° (J/K mol)
S (rhombic)
0
31.880
S (monoclinic)
0.30
32.552
A)
446 K
B)
202 K
C)
–202 K
D)
–446 K
E)
0 K
83. Given the following data (Hf, S°, respectively) for N2O4(l) -20. kJ/mol, 209.0 J/K mol, and
N2O4(g) 10. kJ/mol, 304.2 J/K mol. Above what temperature (in °C) is the vaporization of
N2O4 liquid spontaneous?
A)
Above –178 °C.
B)
Above –231 °C.
C)
Above 3 °C.
D)
Above 30. °C.
E)
Above 42 °C.
84. The reaction 2H2O(g) → 2H2(g) + O2(g) has a positive value of G°. Which of the
following statements must be true?
A)
The reaction is slow.
B)
The reaction will not occur. (When H2O(g) is introduced into a flask, no O2 or H2
will form even over a long period of time.)
C)
The reaction is exothermic.
D)
The equilibrium lies far to the right.
E)
None of these is true.
85. Given the following free energies of formation:
Gf°
C2H2(g)
209.2 kJ/mol
C2H6(g)
–32.92 kJ/mol
calculate Kp at 298 K for C2H2(g) + 2H2(g) C2H6(g)
A)
97.7
B)
1.10
C)
7.95 1030
D)
2.76 1042
E)
None of these is within a factor of 10 of the correct answer.
86. The acid dissociation constant for a weak acid HX at 25°C is 4.3 10–8. Calculate the free
energy of formation for X–(aq) at 25°C. The standard free energies of HX(aq) and H+(aq) at
25°C are –208.3 kJ/mol and 0, respectively.
A)
–205 kJ/mol
B)
250 kJ/mol
C)
0
D)
–166 kJ/mol
E)
–250 kJ/mol
87. The standard molar free energies of formation of NO2(g) and N2O4(g) at 25°C are 51.840
and 98.035 kJ/mol, respectively. What is the value of Kp (in atm) for the reaction written as
follows at 25°C?
2NO2 N2O4
A)
6.24 1011
B)
1.00
C)
9.76
D)
4.38 10–36
E)
7.99 10–9
88. Given that Gf° for NH3 = –16.668 kJ/mol, calculate the equilibrium constant for the
following reaction at 298 K:
N2(g) + 3H2(g) 2NH3(g)
A)
6.97 105
B)
8.35 102
C)
1.01
D)
4.51 1069
E)
5.82 108
89. Calculate Ksp for the salt NaCl at 25°C.
Substance
Gf°(in kJ/mol)
Na+(aq)
–262.0
Cl–(aq)
–131.0
NaCl(s)
383.8
A)
41
B)
1.7 1019
C)
9.2
D)
4.1
E)
0.41
90. Determine G° for the weak acid, HF, at 25°C. (Ka = 7.16 10–4)
A)
1.5 kJ
B)
177 kJ
C)
7.79 kJ
D)
1.77 kJ
E)
17.9 kJ
91. Assume that the reaction:
CO(g) + H2O(g) CO2(g) + H2(g)
occurs in an ideal mixture of ideal gases. At 700. K, Kp = 3.24. At this temperature, G°
equals:
A)
0 kJ
B)
6.84 kJ
C)
–3.42 kJ
D)
–6.84 kJ
E)
–2.97 kJ
92. Consider the reaction:
2SO2(g) 2SO3(g)
for which H° = –200. kJ and S° = –187.1 J/K at 25°C. Assuming that H° and S° are
independent of temperature, calculate the temperature where Kp = 1.
A)
969. K
B)
2069 K
C)
200. K
D)
1069 K
E)
none of these
93. For the following reaction, CO2(g) + 2H2O(g) CH4(g) + 2O2(g), H° = 803 kJ which
of the following will increase K?
A)
decrease number of moles of methane
B)
increase volume of system
C)
increase the temperature of system
D)
all of the above
E)
none of the above
94. For a particular reaction the equilibrium constant is 0.0122 at 370.°C and H° is +16.0 kJ at
25°C. Assuming H° and S° are temperature independent, calculate S° for the reaction.
A)
6.61 J/K
B)
–6.61 J/K
C)
–11.8 J/K
D)
11.8 J/K
E)
none of these
95. Calculate G° for at 600.1 K, using the following data:
H2(g) + O2(g) H2O2(g) Kp = 2.3 106 at 600.1 K
2H2(g) + O2(g) 2H2O(g) Kp = 1.8 1037 at 600.1 K
A)
141 kJ
B)
–501 kJ
C)
501 kJ
D)
–287 kJ
E)
287 kJ
96. Consider the following hypothetical reaction (at 307.8 K). Standard free energies in kJ/mol
are given in parentheses.
A B + C G° = ?
(-32.2) (207.8) (-237.0)
What is the value of the equilibrium constant for the reaction at 307.8 K?
A)
0.31
B)
1.0
C)
9.0 104
D)
273
E)
0.43
97. The equilibrium constant K for the dissociation reaction of a molecule X2
X2(g) 2X(g)
was measured as a function of temperature (in K). A graph of ln K versus 1/T for this
reaction gives a straight line with a slope of –1.352 104 and an intercept of 15.59 K. The
value of S for this dissociation reaction is:
A)
1.875 J/K mol
B)
259.2 J/K mol
C)
129.6 J/K mol
D)
64.81 J/K mol
E)
none of these
98. The following reaction has a G° value of 48.47 kJ/mol at 25°C.
HB(aq) + H2O(l) H3O+(aq) + B–(aq)
Calculate the Ka for the acid HB.
A)
0.981
B)
–19.6
C)
3.19 10–9
D)
4.85 10–5
E)
–233
99. The standard free energy of formation of nitric oxide, NO, at 1000. K (roughly the
temperature in an automobile engine during ignition) is 77.9 kJ/mol. Calculate the
equilibrium constant for the reaction
N2(g) + O2(g) 2NO(g)
at 1000. K.
A)
1.56 105
B)
8.53 10–5
C)
–14.7
D)
7.27 10-9
E)
0.948
100. Consider the reaction 2NO2(g) N2O4(g); H° = –56.8 kJ and S° = –175 J/K. In a
container (at 298 K) N2O4(g) and NO2(g) are mixed with initial partial pressures of 2.4 atm
and 0.42 atm, respectively. Which of the following statements is correct?
A)
Some N2O4(g) will decompose into NO2(g).
B)
Some NO2(g) will dimerize to form N2O4(g).
C)
The system is at equilibrium at these initial pressures.
D)
The final total pressure must be known to answer this question.
E)
None of these.
Consider the gas phase reaction NO + O2 NO2 for which H° = –56.91 kJ and
K = 1.46 106 at 25°C.
101. Calculate H° at 25°C for the following reaction:
2NO + O2 2NO2
A)
56.91 kJ
B)
–113.8 kJ
C)
–28.5 kJ
D)
3239 kJ
E)
none of these
102. Calculate K for the following reaction at 25°C:
2NO + O2 2NO2
A)
2.92 106
B)
2.13 1012
C)
7.30 105
D)
1.21 103
E)
1.46 106
103. Calculate G° at 25°C for the following reaction:
2NO + O2 2NO2
A)
–70.3 kJ
B)
–5.90 kJ
C)
–35.2 kJ
D)
5.90 kJ
E)
70.3 kJ
104. Calculate S° at 25°C for the following reaction:
2NO + O2 2NO2
A)
236 J/K
B)
–146 J/K
C)
–236 J/K
D)
–264 J/K
E)
264 J/K
105. For this system at equilibrium, how will raising the temperature affect the amount of NO
present?
A)
The amount of NO will increase.
B)
The amount of NO will decrease.
C)
The amount of NO will remain the same.
D)
Cannot be determined.
E)
Answer depends on the value of K.
106. What would be the effect on the amount of NO present of compressing the equilibrium
system to a smaller volume, while keeping the temperature constant?
A)
The amount of NO will increase.
B)
The amount of NO will decrease.
C)
The amount of NO will remain the same.
D)
Cannot be determined.
E)
Answer depends on the value of K.
107. Given CH3CO2H(aq) H+(aq) + CH3CO2–(aq) at 25°C, Ka = 1.84 10–5. What is G°
at 25°C?
A)
–27.0 kJ
B)
27.0 kJ
C)
2.27 kJ
D)
–2.27 kJ
E)
27.0 J
108. Given CH3CO2H(aq) H+(aq) + CH3CO2–(aq) at 25°C, Ka = 1.75 10–5. What is G at
25°C for a solution in which the initial concentrations are:
[CH3CO2H]0 = 0.10 M
[H+]0 = 4.8 10–8 M
[CH3CO2–]0 = 0.010 M
A)
–74.6 kJ
B)
74.6 kJ
C)
20.3 kJ
D)
–20.3 kJ
E)
27.1 kJ
109. The equilibrium constant of a certain reaction was measured at various temperatures to give
the plot shown below. What is S° for the reaction in J/mol K?
A)
0.20
B)
3.0
C)
25
D)
–50.
E)
–8.3 103
110. Consider a weak acid, HX. If a 0.10 M solution of HX has a pH of 5.64 at 25°C, what is
G° for the acid’s dissociation reaction at 25°C?
A)
–58.6 kJ
B)
4.92 kJ
C)
0
D)
–4.92 kJ
E)
58.6 kJ
111. For the reaction CO(g) + 2H2(g) CH3OH(g) G°700K = –13.462 kJ. The Kp for this
reaction at 700. K is:
A)
10.1
B)
1.00
C)
1.54
D)
2.31
E)
none of these
112. For the reaction 2HF(g) H2(g) + F2(g), G° = 38.3 kJ, at 1000 K. If, at this
temperature, 5.00 moles of HF(g), 0.500 moles of H2(g), and 0.75 moles of F2(g) are mixed
in a 1.00-L container:
A)
Some HF will decompose (to yield H2 and F2).
B)
The system is at equilibrium.
C)
Some HF will be formed (from H2 and F2).
D)
Not enough data are given to answer this question.
E)
None of these (A-D).
Consider the following system at equilibrium at 25°C:
PCl3(g) + Cl2(g) PCl5(g)
for which H° = –92.5kJ at 25°C.
113. If the temperature of the system is raised, the ratio of the partial pressure of PCl5 to the
partial pressure of PCl3 will
A)
increase
B)
decrease
C)
stay the same
D)
impossible to tell without more information
E)
none of these
114. When some Cl2(g) is added at constant volume and temperature, the ratio of the partial
pressure of PCl5 to the partial pressure of PCl3 will
A)
increase
B)
decrease
C)
stay the same
D)
impossible to tell without more information
E)
none of these
115. When the volume is decreased at constant temperature, the ratio of the partial pressure of
PCl5 to the partial pressure of PCl3 will
A)
increase
B)
decrease
C)
stay the same
D)
impossible to tell without more information
E)
none of these
116. Water gas, a commercial fuel, is made by the reaction of hot coke carbon with steam.
C(s) + H2O(g) CO(g) + H2(g)
When equilibrium is established at 844°C the concentrations of CO, H2, and H2O are
4.00 10–2, 4.00 10–2, and 1.00 10–2 mole/liter, respectively. Calculate the value of G°
for this reaction at 844°C.
A)
12.9 kJ
B)
–12.87 kJ
C)
55.64 kJ
D)
17.02 kJ
E)
none of these
The equilibrium constant Kp (in atm) for the dissociation reaction of Cl2 2Cl was
measured as a function of temperature (in K). A graph of ln Kp versus 1/T for this reaction
gives a straight line with a slope of –1.651 104 and an intercept of 14.51.
117. From these data, which of the following statements is true?
A)
The reaction is exothermic.
B)
The reaction is endothermic.
C)
The reaction rate is high
D)
The reaction is not spontaneous.
E)
None of these.
118. The value of H for this dissociation reaction is:
A)
–137.3 kJ
B)
137.3 kJ
C)
1.986 kJ
D)
–1.986 kJ
E)
none of these
119. For a certain process, at 300. K, G = –10.4 kJ and H = –7.0 kJ. If the process is carried
out reversibly, the amount of useful work that can be performed is
A)
–17.4 kJ
B)
–7.0 kJ
C)
–3.4 kJ
D)
–10.4 kJ
E)
3.4 kJ
120. For a certain process, at 300. K, G = –12.2 kJ and H = –7.0 kJ. If the process is carried
out so that no useful work is performed, G is
A)
12.2 kJ
B)
7.0 kJ
C)
0
D)
–7.0 kJ
E)
–12.2 kJ
121. Which statement is true?
A)
All real processes are irreversible.
B)
A thermodynamically reversible process takes place infinitely fast.
C)
In a reversible process, the state functions of the system are always much greater
than those of the surroundings.
D)
There is always more heat given off to the surroundings in a reversible process
than in an unharnessed one.
E)
All statements (A–D) are true.
Would you predict an increase or decrease in entropy for each of the following?
122. The freezing of water
123. He(g) at 3 atm → He(g) at 1 atm
124. 2H2(g) + O2(g) → 2H2O(g)
125. 2KClO3(s) → 2KCl(s) + 3O2(g)