Ch 10 Practice Problems
1.
Consider the process A(l)
A(s). Which direction favors positional randomness?
A) to the right
B) to the left
C) neither
D) It depends on the temperature.
2.
Consider the process A(l)
A(s). An increase in temperature favors which direction?
A) to the right
B) to the left
C) neither
D) More information is needed.
3.
A mixture of hydrogen and chlorine remains unreacted until it is exposed to ultraviolet light from a burning magnesium strip.
Then the following reaction occurs very rapidly.
H2(g) + Cl2(g)  2HCl(g)
G = –45.54 kJ
H = –44.12 kJ
S = –4.76 J/K
Select the statement below that best explains this behavior.
A)
B)
C)
D)
E)
4.
The reactants are thermodynamically more stable than the products.
The reaction has a small equilibrium constant.
The ultraviolet light raises the temperature of the system and makes the reaction more favorable.
The negative value for S slows down the reaction.
The reaction is spontaneous, but the reactants are kinetically stable.
Consider the dissociation reaction of the acid HF
HF(aq)
H+(aq) + F-(aq)
Why is S negative?
A)
B)
C)
D)
E)
5.
Each HF molecule produces two ions when it dissociates.
The ions are hydrated.
The reaction is expected to be exothermic, and S thus should be negative.
The reaction is expected to be endothermic, and thus S should be negative.
none of these
Which of the following result(s) in an increase in the entropy of the system?
I. (See diagram.)
II. Br2(g)  Br2(l)
III. NaBr(s)  Na+(aq) + Br–(aq)
IV. O2(298 K)  O2(373 K)
V. NH3(1 atm, 298 K)  NH3(3 atm, 298 K)
A)
B)
C)
D)
E)
I
II, V
I, III, IV
I, II, III, IV
I, II, III, V
6.
Calculate S when One mole of an ideal gas is compressed isothermally at 607.4 K from 5.60 atm to 8.90 atm. If the
process is carried out in two irreversible steps (intermediate step at P = 7.00 atm).
A) 2.34 J/K
B) -2.34 J/K
C) -3.85 J/K
D) 3.85 J/K
E)
0 J/K
Use the following to answer questions 7-8:
One mole of an ideal gas expands isothermally and reversibly at 0°C. The pressure on 1 mol of an ideal monatomic gas changes
from 100.0 atm to 1.00 atm.
7.
Calculate w.
A) 225 kJ
B) -225 kJ
C) 10.5 kJ
D) -10.5 kJ
E)
0
8.
Calculate q.
A) 225 kJ
B) -225 kJ
C) 10.5 kJ
D) -10.5 kJ
E)
0
Use the following to answer questions 9-15:
A gas expands isothermally and irreversibly.
9.
10.
11.
12.
13.
14.
w is
A) less than zero.
B) equal to zero.
C) greater than zero.
D) More information is needed.
q is
A) less than zero.
B) equal to zero.
C) greater than zero.
D) More information is needed.
H is
A) less than zero.
B) equal to zero.
C) greater than zero.
D) More information is needed.
E is
A) less than zero.
B) equal to zero.
C) greater than zero.
D) More information is needed.
S is
A) less than zero.
B) equal to zero.
C) greater than zero.
D) More information is needed.
Ssurr is
A) less than zero.
B) equal to zero.
C) greater than zero.
D) More information is needed.
15.
G is
A) less than zero.
B) equal to zero.
C) greater than zero.
D) More information is needed.
Use the following to answer questions 16-18:
One mole of an ideal gas is compressed isothermally and reversibly at 607.4 K from 5.60 atm to 8.90 atm.
16.
Calculate q.
A) 298 kJ
B) -2.34 kJ
C) 2.34 kJ
D) -298 kJ
E)
none of these
17.
Calculate w.
A) 298 kJ
B) -2.34 kJ
C) 2.34 kJ
D) -298 kJ
E)
none of these
18.
Calculate H.
A) 0 kJ
B) -2.34 kJ
C) 2.34 kJ
D) 3.85 kJ
E)
none of these
Use the following to answer questions 19-21:
In an isothermal process, the pressure on 1 mol of an ideal monatomic gas suddenly changes from 4.00 atm to 100.0 atm at
25°C.
19.
Calculate T.
A) 25°C
B) 48°C
C) 100°C
D) 0°C
E)
none of these
20.
Calculate V.
A) 5.87 L
B) -5.87 L
C) 6.11 L
D) -6.11 L
E)
none of these
21.
Calculate w.
A) -59.5 kJ
B) 59.5 kJ
C) 23.5 kJ
D) -23.5 kJ
E)
0
22.
One mole of an ideal gas at 25°C is expanded isothermally from 5.0 L to 10.0 L under such conditions that no work is produced
in the surroundings. Which statement is correct?
A) Sgas = 0
B) Sgas = Rln2/298
C) Suniv = 0
D) Ssurr = 0
E)
Sgas = Ssurr
23.
A rigid insulated box contains 20.0 g of He(g) at 25.0° C and 1.00 atm in one compartment and 20.0 g of N 2(g) at 115° C and
2.00 atm in the other compartment. These compartments are connected by a partition that transmits heat. What is the final
temperature in the box at thermal equilibrium? (Cv(He) = 12.5 J/K•mol; Cv(N2) = 20.7 J/K•mol)
A) 42.3°C
B) 58.9°C
C) 70.0°C
D) 81.0°C
E)
none of these
24.
One mole of an ideal gas at 25°C is expanded isothermally and reversibly from 125.0 L to 250.0 L. Which statement is correct?
A) Sgas = 0
B) Sgas = Rln2
C) Suniv = 0
D) Ssurr = 0
E)
Sgas = Ssurr
25.
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 these statements are true.
26.
A machine employs the isothermal expansion of 1 mol of an ideal gas from 4.50 L to 15.0 L. At 25°C, the machine performs
3.00 kJ of work. What percent of the maximum possible work is the machine producing?
A) 4.50%
B) 50.3%
C) 0.60%
D) 15.0%
E)
This amount of work cannot be correct.
Use the following to answer question 27:
In an isothermal process, the pressure on 1 mol of an ideal monatomic gas suddenly changes from 4.00 atm to 100.0 atm at
25°C.
27.
Calculate E.
A) 59.5 kJ
B) 119 kJ
C) -59.5 kJ
D) 0 kJ
E)
none of these
28.
If the change in entropy of the surroundings for a process at 451 K and constant pressure is –348 J/K, what is the heat flow
absorbed by the system?
A) 772 kJ
B) 18.9 kJ
C) –157 kJ
D) -18.9 kJ
E)
157 kJ
Use the following to answer question 29:
One mole of an ideal gas expands isothermally and reversibly at 0°C. The pressure on 1 mol of an ideal monatomic gas changes
from 100.0 atm to 1.00 atm.
29.
Calculate E.
A) 450 kJ
B) -450 kJ
C) 21.0 kJ
D) -21.0 kJ
E)
none of these
Use the following to answer question 30:
One mole of an ideal gas is compressed isothermally and reversibly at 607.4 K from 5.60 atm to 8.90 atm.
30.
Calculate S.
A) 2.34 J/K
B) -2.34 J/K
C) -3.85 J/K
D) 3.85 J/K
E)
0
31.
S is _______ for exothermic reactions and ______ for endothermic reactions.
A) favorable, unfavorable
B) unfavorable, favorable
C) favorable, favorable
D) unfavorable, unfavorable
E)
cannot tell
32.
1.2 mol of an ideal gas at 304 K is compressed isothermally and reversibly from 1.8 L to 0.50 L. What is S?
A) 13 J/K
B) –3.9 kJ/K
C) –11 J/K
D) –13 J/K
E)
–6 J/K
33.
In a certain reversible expansion, a system at 300. K absorbs exactly 6.00  102 J of heat. In the irreversible recompression to
the original state of the system, twice as much work is done on the system as is performed on the surroundings in the expansion.
What is the entropy change of the system in the recompression step?
A) -4.00 J/K
B) -2.00 J/K
C) 0.00 J/K
D) 2.00 J/K
E)
4.00 J/K
34.
Calculate G for the isothermal compression of 1 mol of an ideal monatomic gas from 1.4 atm to 5.6 atm at 23°C.
A) 3.4  103 J
B) 1.6  103 J
C) -3.4  103 J
D) -1.6  103 J
E)
5.1 103 J
35.
Calculate the entropy change when 5.00 mol of a monatomic ideal gas is cooled from 135°C to 85°C at 1 atm.
A) -250.0 J/K
B) -9.62 J/K
C) -48.9 J/K
D) -13.6 J/K
E)
-2.74 J/K
36.
Which of the following is true?
A) As long as the disorder of the surroundings is increasing, a process will be spontaneous.
B) For any process, Ssurr and Ssys have opposite signs.
C) If Ssurr = -Ssys , the process is at equilibrium.
D) H° is zero for a chemical reaction at constant temperature.
E)
none of these
37.
Ssurr
A)
B)
C)
D)
E)
is _______ for exothermic reactions and ______ for endothermic reactions.
favorable, unfavorable
unfavorable, favorable
favorable, favorable
unfavorable, unfavorable
cannot tell
Use the following to answer questions 38-40:
At 1 atm, a liquid is heated above its normal boiling point.
38.
Ssurr for this process is
A) greater than zero.
B) less than zero.
C) equal to zero.
D) cannot be determined
39.
S for this process is
A) greater than zero.
B) less than zero.
C) equal to zero.
D) cannot be determined
40.
Suniv for this process is
A) greater than zero.
B) less than zero.
C) equal to zero.
D) cannot be determined
41.
Choose the correct statement.
A) Exothermic reactions are always spontaneous.
B) Free energy is independent of temperature.
C) A reaction that exhibits a negative value of S cannot be spontaneous.
D) At constant pressure and temperature, a decrease in free energy ensures an increase in the entropy of the system.
E)
none of these
42.
For which process is S negative?
A) evaporation of 1 mol of CCl4(l)
B) mixing 5 mL of ethanol with 25 mL of water
C) compressing 1 mol of Ne at constant temperature from 1.5 atm to 0.5 atm
D) raising the temperature of 100 g of Cu from 275 K to 295 K
E)
grinding a large crystal of KCl to powder
43.
When a gas is expanded isothermally and reversibly at 38°C, the work done is -42.6 kJ. Calculate S.
A) 1121 J/K
B) 1.12 kJ/K
C) 1.37  102 J/K
D) -1139 J/K
E)
-1.12 kJ/K
44.
A 100-mL sample of water is placed in a coffee cup calorimeter. When 1.0 g of an ionic solid is added, the temperature
decreases from 21.5°C to 20.8°C as the solid dissolves. Which of the following is true for the dissolving of the solid?
A) H < 0
B) Suniv > 0
C) Ssys< 0
D) Ssurr > 0
E)
none of these
Use the following to answer questions 45-49:
The process
H2O(g)  H2O(l)
takes place at 1 atm and 95°C.
45.
What is w?
A) less than zero
B) equal to zero
C) greater than zero
D) More information is needed.
46.
What is q?
A) less than zero
B) equal to zero
C) greater than zero
D) More information is needed.
47.
What is H?
A) less than zero
B) equal to zero
C) greater than zero
D) More information is needed.
48.
What is S?
A) less than zero
B) equal to zero
C) greater than zero
D) More information is needed.
49.
What is G?
A) less than zero
B) equal to zero
C) greater than zero
D) More information is needed.
50.
Assume that the enthalpy of fusion of ice is 6020 J/mol and does not vary appreciably over the temperature range 270–290 K. If
2.20 mol of ice at 0°C is melted by heat supplied from surroundings at 284 K, what is the entropy change in the surroundings in
J/K?
A) +48.5
B) +45.5
C) 0.0
D) –45.5
E)
–48.5
51.
5.50 mol of a monatomic ideal gas is cooled from 246°C to 27°C at constant volume. Calculate S.
A) –62.7 J/K
B) –16.3 J/K
C) –27.2 J/K
D) –37.6 J/K
E)
–1.52  102 J/K
52.
Calculate the minimum work required to compress 1.9 mol of an ideal monatomic gas from 47.4 L to 15.6 L at 27°C.
A) 4.7  102 J
B) -7.9  103 J
C) 7.9  103 J
D) 5.3  103 J
E)
2.8  102 J
53.
Calculate S for cooling 2.60 mol of an ideal monatomic gas from 87°C to 41°C at constant volume.
A) –24.4 J/K
B) –4.43 J/K
C) –2.96 J/K
D) –16.3 J/K
E)
–1.70 J/K
54.
Calculate S for cooling 1.5 mol of an ideal monatomic gas from 81°C to 36°C at constant pressure.
A) –1.70 J/K
B) –25.3 J/K
C) –4.24 J/K
D) –2.54 J/K
E)
–2.83 J/K
55.
Calculate S for an isothermal (95°C) expansion of 2 mol of a monatomic ideal gas from 100.0 atm to 1.00 atm.
A) 76.6 J/K
B) -76.6 J/K
C) -38.3 J/K
D) 38.3 J/K
E)
none
Use the following to answer questions 56-57:
Substance X has a heat of vaporization of 55.4 kJ/mol at its normal boiling point (423°C). For the process X( l)  X(g) at 1 atm
and 423°C, calculate the value of:
56.
57.
G
A)
B)
C)
D)
E)
0
79.6 J/K•mol
103 J/K•mol
-79.6 J/K•mol
-103 J/K•mol
Suniv
A) 0
B) 79.6 J/K•mol
C) 103 J/K•mol
D) -79.6 J/K•mol
E)
-103 J/K•mol
Use the following to answer questions 58-59:
In an isothermal process, the pressure on 1 mol of an ideal monatomic gas suddenly changes from 4.00 atm to 100.0 atm at
25°C.
58.
Calculate G.
A) 7.98 kJ
B) -7.98 kJ
C) 59.5 kJ
D) 0 kJ
E)
none of these
59.
Calculate S.
A) 20.5 J/K
B) -20.5 J/K
C) 26.8 J/K
D) -26.8 J/K
E)
none of these
Use the following to answer questions 60-61:
Substance X has a heat of vaporization of 55.4 kJ/mol at its normal boiling point (423°C). For the process X( l)  X(g) at 1 atm
and 423°C, calculate the value of:
60.
61.
Ssurr
A)
B)
C)
D)
E)
0
79.6 J/K•mol
103 J/K•mol
-79.6 J/K•mol
-103 J/K•mol
S
A)
B)
C)
D)
E)
0
79.6 J/K•mol
103 J/K•mol
-79.6 J/K•mol
-103 J/K•mol
62.
Consider the freezing of liquid water at –10°C. For this process what are the signs for H, S, and G, respectively?
A) +
–
0
B) –
+
0
C) –
+
–
D) +
–
–
E)
–
–
–
63.
In which case must a reaction be spontaneous at all temperatures?
A) H is positive, S is positive
B) H = 0, S is negative
C) S = 0, H is positive
D) H is negative, S is positive
E)
none of these
64.
The dissociation of hydrogen
H2(g)
2H(g)
A)
B)
C)
D)
E)
is spontaneous at any temperature.
is spontaneous at high temperature.
is spontaneous at low temperature.
is independent of temperature.
never takes place.
Use the following to answer question 65:
In an isothermal process, the pressure on 1 mol of an ideal monatomic gas suddenly changes from 4.00 atm to 100.0 atm at
25°C.
65.
Calculate H.
A) 59.5 kJ
B) -119 kJ
C) -59.5 kJ
D) 0 kJ
E)
none of these
66.
As O2(l) is cooled at 1 atm, it freezes at 54.5 K to form Solid I. At a lower temperature, Solid I rearranges to Solid II, which has
a different crystal structure. Thermal measurements show that H for the I  II phase transition is –743.1 J/mol and that S for
the same transition is –17.0 J/K mol. At what temperature are Solids I and II in equilibrium?
A) 2.06 K
B) 43.7 K
C) 31.5 K
D) 53.4 K
E)
They can never be in equilibrium because they are both solids.
67.
When a stable diatomic molecule spontaneously forms from its atoms, what are the signs of H°, S°, and G°, respectively?
A) +
+
+
B) +
–
–
C) –
+
+
D) –
–
+
E)
–
–
–
Use the following to answer question 68:
Consider the reaction
2N2O5(g)
4NO2(g) + O 2(g)
at 25°C, for which the following data are relevant:
H°f (kJ/mol)
N2O5
11.29
NO2
33.15
O2
?
S° (J/K•mol)
355.3
239.9
204.8
68.
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.
69.
Elemental sulfur exists in two crystalline forms, rhombic and monoclinic. From the following data, calculate the temperature at
which monoclinic sulfur and rhombic sulfur are in equilibrium.
S (rhombic)
S (monoclinic)
A)
B)
C)
D)
E)
70.
Hf° (kJ/mol)
0
0.30
S° (J/K•mol)
31.88
32.55
+450 K
+210 K
–210 K
–450 K
0K
For a spontaneous endothermic process, which conditions must hold?
1) wmax = G
2) Ssurr > 0
3) S cannot be negative.
4) S is positive.
A) all
B) none
C) 1 and 3 only
D) 1, 2, and 4 only
E) 3 and 4 only
71.
For the vaporization of a liquid at a given pressure,
A) G is positive at all temperatures.
B) G is negative at all temperatures.
C) G is positive at low temperatures but negative at high temperatures (and zero at some temperature).
D) G is negative at low temperatures but positive at high temperatures (and zero at some temperature).
72.
For the reaction A + B  C + D, H° = +40 kJ and S° = +50 J/K. Therefore, the reaction under standard conditions is
A) spontaneous at temperatures less than 10 K.
B) spontaneous at temperatures greater than 800 K.
C) spontaneous only at temperatures between 10 K and 800 K.
D) spontaneous at all temperatures.
E)
nonspontaneous at all temperatures.
73.
For the process involving compound A: A(s)  A(l), H° = 7.5 kJ/mol, and S° = 43.4 J/mol•K. What is the melting point of
compound A?
A) –100°C
B) 173°C
C) –222°C
D) 100°C
E)
–173°C
74.
Given the following data, calculate the normal boiling point for formic acid (HCOOH).
S° (J/K•mol)
H°f (kJ/mol)
HCOOH(l)
-410.
130.
HCOOH(g)
-363
251
A)
B)
C)
D)
E)
75.
2.57 K
1730°C
388°C
82°C
115°C
At constant pressure, the reaction
2NO2(g)  N2O4(g)
is exothermic. The reaction (as written) is
A)
B)
C)
D)
always spontaneous.
spontaneous at low temperatures but not at high temperatures.
spontaneous at high temperatures but not at low temperatures.
never spontaneous.
For the process moleene(l)  moleene(g) at 1 atm, Hvap = 37.6 kJ/mol and Svap = 67.8 J/mol•K. Assuming these values
are independent of T, what is the normal boiling point of moleene?
A) 828°C
B) 282°C
C) 378°C
D) –282°C
E)
555°C
Use the following to answer questions 77-80:
76.
The vapor pressure of Br 2(l) at 25°C is 0.281 atm, and 193 J is required to vaporize 1.00 g of bromine at 1 atm pressure.
77.
Calculate H° for the vaporization of Br2(l) at 25°C and 1 atm.
A) 0.193 kJ/mol
B) 30.8 kJ/mol
C) 15.4 kJ/mol
D) 1.21 kJ/mol
E)
none of these
78.
Calculate S° for the vaporization of Br2(l) at 25°C and 1 atm.
A) 92.8 J/K•mol
B) 103 J/K•mol
C) 0 J/K•mol
D) 30.8 J/K•mol
E)
none of these
79.
Assuming H° and S° are temperature independent, calculate the normal boiling point of bromine.
A) 25°C
B) 332°C
C) 332 K
D) 0°C
E)
none of these
80.
Calculate G for the vaporization of Br2(l) at 25°C and 1 atm.
A) 0.378 kJ/mol
B) 0.263 kJ/mol
C) 3.15 kJ/mol
D) 0
E)
none of these
81.
In which reaction is S° expected to be positive?
A) I2(g)  I2(s)
B) H2O(1) H2O(s)
C) CH3OH(g) + (3/2)O2(g)  CO2(g) + 2H2O(l)
D) 2O2(g) + 2SO(g)  2SO3(g)
E)
none of these
Use the following to answer question 82:
Consider the reaction
2N2O5(g)
4NO2(g) + O 2(g)
at 25°C, for which the following data are relevant:
H°f (kJ/mol)
N2O5
11.29
NO2
33.15
O2
?
S° (J/K•mol)
355.3
239.9
204.8
82.
Calculate S° for the reaction.
A) 89.5 J/K
B) -249.2 J/K
C) 453.8 J/K
D) 249.2 J/K
E)
–115.6 J/K
83.
For which of the following processes would S° be expected to be most positive?
A) O2(g) + 2H2(g)  2H2O(g)
B) H2O(l)  H2O(s)
C) NH3(g) + HCl(g)  NH4Cl(g)
D) 2NH4NO3(s)  2N2(g) + O2(g) + 4H2O(g)
E)
N2O4(g)  2NO2(g)
84.
Consider the following hypothetical reaction at 340 K. Standard free energies of formation are given in parentheses.
B
G° = –38.4 kJ/mol
 C
(?)
(165.5 kJ/mol)
Calculate the standard free energy of formation of compound B.
A)
B)
C)
D)
E)
203.9 kJ/mol
127.1 kJ/mol
-203.9 kJ/mol
–127.1 kJ/mol
–292.6 kJ/mol
85.
The standard free energy of formation of AgBr(s) is –97.0 kJ/mol. Calculate G° for the reaction
2AgBr(s)  2Ag(s) + Br2(g)
A)
B)
C)
D)
E)
86.
97.0 kJ
194 kJ
–97.0 kJ
–194 kJ
44.0 kJ
The reaction
2H2O(g)  2H2(g) + O2(g)
has a positive value of G°. Which of the following statements must be true?
A)
B)
C)
D)
E)
The reaction is slow.
The reaction will not occur. That is, when H 2O(g) is introduced into a flask, no O2 or H2 will form even over a long period
of time.
The reaction is exothermic.
The equilibrium lies far to the right.
None of these is true.
87.
The standard free energy of formation of N2(g) at 25°C is zero. Calculate Gf (25°C), in kilojoules per mol, for N2 at 1000 atm.
Assume ideal gas behavior.
A) +39.4 kJ/mol
B) +17.1 kJ/mol
C) 0 kJ/mol
D) –17.1 kJ/mol
E)
-39.4 kJ/mol
88.
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 1.00 atm pressure.
A) –3.5 kJ
B) –36.6 kJ
C) +36.6 kJ
D) –50.0 kJ
E)
+50.0 kJ
Use the following to answer questions 89-90:
Given
CH3CO2H(aq)
at 25°C, Ka = 1.8  10 –5
89.
What is G at 25°C for a solution in which the initial concentrations are
[CH3CO2H]o = 0.10 M
[H+]o = 2.0  10 –8 M
[CH3CO2–]o = 0.010 M
A)
B)
C)
D)
E)
90.
H+(aq) + CH 3CO2–(aq)
+50. kJ
–50. kJ
+23 kJ
–23 kJ
27 kJ
What is G° at 25°C?
A) –27,000 J
B) +27,000 J
C) –2300 J
D) +2300 J
E)
+270 J
Use the following to answer questions 91-93:
Consider the reaction
2N2O5(g)
4NO2(g) + O 2(g)
at 25°C, for which the following data are relevant:
H°f (kJ/mol)
N2O5
11.29
NO2
33.15
O2
?
S° (J/K•mol)
355.3
239.9
204.8
91.
Calculate H° for the reaction.
A) 110.02 kJ
B) 21.86 kJ
C) –21.86 kJ
D) 115.20 kJ
E)
–155.20 kJ
92.
Calculate G° for the reaction at 25°C.
A) –135 kJ
B) 98.7 kJ
C) –25.2 kJ
D) –11.2 kJ
E)
0
93.
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) –135 kJ
B) 98.7 kJ
C) –25.2 kJ
D) –11.2 kJ
E)
0
94.
For the reaction
CO2(g) + 2H2O(g)  CH4(g) + 2O2(g), H° = 803 kJ
which of the following will increase K?
A)
B)
C)
D)
E)
95.
decreasing the number of moles of methane
increasing the volume of system
increasing the temperature of system
all of these
none of these
Assume that the reaction
CO(g) + H2O(g)
CO2(g) + H2(g)
occurs in an mixture of ideal gases. At 700 K, Kp = 5.10. At this temperature, what is G°?
A)
B)
C)
D)
E)
96.
0 kJ
29.7 kJ
9.48 kJ
–9.48 kJ
–4.12 kJ
The equilibrium constant Kp for the dissociation reaction of Cl2
Cl2(g)
2Cl(g)
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 –1.352  104 and an intercept of 14.51. What is the value of S for this dissociation reaction?
A) 26.81 J/K•mol
B) 112.0 J/K•mol
C) 120.6 J/K•mol
D) 53.14 J/K•mol
E) none of these
97.
The following reaction has a G° value of 42.6 kJ/mol at 25°C.
HB(aq) + H2O(l)
H3O+(aq) + B–(aq)
Calculate Ka for the acid HB.
A)
B)
C)
D)
E)
1.63
–17.2
3.41  10–8
42,600
14.0
Use the following to answer questions 98-103:
Consider the gas phase reaction
NO + (1/2)O2
NO2
for which H° = –57.0 kJ and K = 1.5  10 6 at 25°C.
98.
Calculate H° at 25°C for the following reaction:
2NO + O2
2NO2
A)
B)
C)
D)
99.
57.0 kJ
–114 kJ
–28.5 kJ
778 kJ
Calculate K for the following reaction at 25°C:
2NO + O2
2NO2
A)
B)
C)
D)
E)
3.0  106
2.3  1012
7.5  105
1.2  103
1.5  106
100. Calculate G° at 25°C for the following reaction:
2NO + O2
2NO2
A)
B)
C)
D)
E)
–70.5 kJ
–5.91 kJ
–57.0 kJ
+5.91 kJ
+70.5 kJ
101. Calculate S° at 25°C for the following reaction:
2NO + O2
2NO2
A)
B)
C)
D)
E)
–1740 J/K
–146 J/K
+528 J/K
+146 J/K
+1740 J/K
102. 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.
103. What will 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.
104. The standard free energy of formation of nitric oxide, NO, at 1000. K (roughly the temperature in an automobile engine during
ignition) is 78 kJ/mol. Calculate the equilibrium constant for the reaction
N2(g) + O2(g)
2NO(g)
at 1000. K.
A)
B)
C)
D)
E)
1.8  10–19
0.99
4.3  10–10
7.1  10–9
8.4  10–5
Use the following to answer questions 105-107:
Consider the following system at equilibrium at 25°C:
PCl3(g) + Cl2(g)
PCl5(g)
for which H° = –92.5 kJ at 25°C.
105. When the temperature of the system is raised, the ratio of the partial pressure of PCl 5 to the partial pressure of PCl3 will
A) increase.
B) decrease.
C) stay the same.
D) It is impossible to tell without more information.
106. When some Cl2(g) is added at constant volume and temperature, the ratio of the partial pressure of PCl 5 to the partial pressure of
PCl3 will
A) increase.
B) decrease.
C) stay the same.
D) It is impossible to tell without more information.
107. When the volume is decreased at constant temperature, the ratio of the partial pressure of PCl 5 to the partial pressure of PCl3
will
A) increase.
B) decrease.
C) stay the same.
D) It is impossible to tell without more information.
108. Consider a weak acid, HX. The value of G° for the acid's dissociation reaction at 25°C is 42.6 kJ. Determine the value of Ka
for the acid.
A) 1.63
B) 3.41  10–8
C) 4.26  105
D) 2.86  10–6
E)
none of these
Use the following to answer questions 109-110:
The equilibrium constant Kp (in atm) for the dissociation reaction of Cl 2
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 –1.352  104 and an intercept of 14.51.
109. From these data, which of the following statements is true?
A) The reaction is exothermic.
B) The reaction is endothermic.
C) The reaction is spontaneous.
D) None of these statements is true.
110. What is the value of H for this dissociation reaction?
A) –122.1 kJ
B) 112.4 kJ
C) 26.8 kJ
D) 122.1 kJ
E)
none of these
111. Given the following free energies of formation:
G
C2H2(g)
209.2 kJ/mol
C2H6(g)
–32.9 kJ/mol
calculate Kp at 298 K for C2H2(g) + 2H2(g)
A)
B)
C)
D)
E)
C2H6(g).
9.07  10–1
97.2
1.24  1031
2.72  1042
None of these is within a factor of 10 of the correct answer.
112. The acid dissociation constant for a weak acid HX at 25°C is 2.04  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 –328.2 kJ/mol and 0, respectively.
A) 284 kJ/mol
B) 372 kJ/mol
C) -309 kJ/mol
D) –284 kJ/mol
E)
-372 kJ/mol
113. The standard molar free energies of formation of NO 2(g) and N2O4(g) at 25°C are 51.84 and 98.28 kJ/mol, respectively. What is
the value of Kp (in atm) for the reaction written as follows at 25°C?
2NO2
N2O4
A)
B)
C)
D)
E)
1.37  108
1.17  104
8.84
0.113
7.31  10–9
114. For the reaction Cl2O(g) + (3/2)O2(g)  2ClO2(g), H° = 126.4 kJ/mol and S° = –74.9 J/Kmol. What is G° at 377°C?
A) 98.3 kJ/mol
B) 77.8 kJ/mol
C) 175.1 kJ/mol
D) 51.5 kJ/mol
E)
none of these
115. Given that G°f for NH3 = –16.67 kJ/mol, calculate the equilibrium constant for the following reaction at 298 K.
N2(g) + 3H2(g)
2NH3(g)
A)
B)
C)
D)
E)
6.98  105
8.36  102
8.36  10–2
1.20  10–3
1.42  10–6
116. Consider the reaction
2SO2(g) + O2(g)
2SO3(g)
for which H° = –200. kJ and S° = –187 J/K at 25°C. Assuming that H° and S° are independent of temperature, calculate
the temperature where Kp = 1.
A)
B)
C)
D)
E)
970. K
2070 K
200. K
1070 K
none of these
117. For a particular reaction, the equilibrium constant is 1.60  10–2 at 326°C, and H° is +12.2 kJ at 25°C. Assuming H° and S°
are temperature independent, calculate S° for the reaction.
A) 14.0 J/K
B) 54.7 J/K
C) –14.0 J/K
D) –54.7 J/K
E)
5.44 J/K
118. Calculate G° for H2O(g) + 1/2O2(g)
H2O2(g) at 600. K, using the following data:
H2(g) + O2(g)
H2O2
Kp = 2.3  106 at 600. K
2H2(g) + O2(g)
A)
B)
C)
D)
E)
2H2O(g)
Kp = 1.8  1037 at 600. K
+140 kJ
–220 kJ
–290 kJ
–350 kJ
+290 kJ
119. Consider the following hypothetical reaction (at 319 K). Standard free energies, in kJ/mol, are given in parentheses.
A
B
+
C
G° = ?

(–32.6)
(207.8)
(–237.0)
What is the value of the equilibrium constant for the reaction at 319 K?
A)
B)
C)
D)
E)
0.28
0.10
1.0
3.4  1010
1.3
120. Consider the reaction
2NO2(g)
N2O4(g); H° = –56.8 kJ
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)
B)
C)
D)
E)
Some N2O4(g) will decompose into NO2(g).
Some NO2(g) will dimerize to form N2O4(g).
The system is at equilibrium at these initial pressures.
The final total pressure must be known to answer this question.
None of these statements is correct.
121. Given that S° = 131 J/Kmol for H2(g), estimate the value of S° for the reaction
Ti(s) + H 2(g)  TiH2(s)
A)
B)
C)
D)
E)
0
262 J/K
131 J/K
–131 J/K
–262 J/K
122. For the reaction CO(g) + 2H2(g)
A) 10.1
B) 16.7
C) 22.5
D) 9.90  10–2
E)
none of these
CH3OH(g), G°700K = –13.46 kJ. What is Kp for this reaction at 700. K?
123. For the reaction 2HF(g)
H2(g) + F2(g), G° = 38.3 kJ at 1000 K. If, at this temperature, 5.00 mol of HF(g), 0.500 mol of
H2(g), and 0.75 mol 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.
124. 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 800°C, the concentrations of CO, H 2, and H2O are
4.00  10-2 mol/L, 4.00  10-2 mol/L, and 1.00  10-2 mol/L, respectively. Calculate the value of G° for this reaction at 800°C.
A)
B)
C)
D)
E)
109 kJ
–43.5 kJ
193 kJ
16.3 kJ
none of these
125. For a certain process, at 313 K, G = –22.5 kJ and H = –7.00 kJ. If the process is carried out reversibly, what is the amount of
useful work that can be performed?
A) –49.5 kJ
B) –7.00 kJ
C) –15.5 kJ
D) –22.5 kJ
E)
–29.5 kJ
126. For a certain process, at 322 K, G = –16.0 kJ and H = –5.00 kJ. If the process is carried out in such a way that no useful work
is performed, what is G?
A) 16.0 kJ
B) 11.0 kJ
C) 0
D) –11.0 kJ
E)
–16.0 kJ
127. In which of the following changes is the work done by the system the largest at 25°C?
A) an isothermal free expansion of an ideal gas from 1 L to 10 L
B) an isothermal expansion of an ideal gas from 1 L to 10 L against an opposing pressure of 1 atm
C) an isothermal expansion of an ideal gas from 1 L to 10 L against an opposing pressure of 5 atm
D) an isothermal reversible expansion of an ideal gas from 1 L to 10 L
E)
The work is the same for all these processes.
Use the following to answer question 128:
One mole of an ideal gas is compressed isothermally at 607.4 K from 5.60 atm to 8.90 atm. If the process is carried out in two
irreversible steps (intermediate step at P = 7.00 atm), calculate the following.
128. wtotal
A)
B)
C)
D)
E)
-2.63 kJ
2.63 kJ
-2.34 kJ
2.34 kJ
none of these
129. A 1.00-mol sample of an ideal monatomic gas is compressed isothermally and irreversibly in one step from 2.50 atm to 6.50 atm
at 300.0 K. Calculate w, H, G, and Ssurr for this process.
130. For the process A(l)  A(g), H° = 4.50 kJ/mol at 100.0°C and 1 atm. At constant pressure, the molar heat capacities (Cp) are
as follows: A(l), 65.0 J/K•mol; A(g), 28.0 J/K•mol. Calculate H° for this process at 75.0°C.
131. Calculate w and E when 1 mol of a liquid is vaporized at its normal boiling point (80.0°C). H for the vaporization of the
liquid is 30.7 kJ/mol.
132. Consider the reaction below at 25°C, for which the following data are relevant.
2N2O5(g)
4NO2(g) + O2(g)
N2O5(g)
NO2(g)
O2(g)
H°f (kJ/mol)
-42
34
0
Calculate H°, S°, and G° for this reaction at 25°C.
S° (J/K•mol)
178
240
205
Answers
1. B
2. B
3. E
4. B
5. C
6. C
7. D
8. C
9. A
10. C
101.
102.
103.
104.
105.
106.
107.
108.
109.
110.
129.
130.
131.
132.
B
A
B
D
B
A
A
B
B
B
11.
12.
13.
14.
15.
16.
17.
18.
19.
20.
111.
112.
113.
114.
115.
116.
117.
118.
119.
120.
B
B
C
A
A
B
C
A
D
B
21.
22.
23.
24.
25.
26.
27.
28.
29.
30.
D
D
C
C
A
D
C
A
A
A
B
D
A
C
A
E
D
E
E
C
121.
122.
123.
124.
125.
126.
127.
128.
31.
32.
33.
34.
35.
36.
37.
38.
39.
40.
E
D
B
A
D
C
A
B
A
A
41.
42.
43.
44.
45.
46.
47.
48.
49.
50.
E
C
C
B
C
A
A
A
A
D
51.
52.
53.
54.
55.
56.
57.
58.
59.
60.
D
D
B
C
A
A
A
A
D
D
D
A
C
D
D
E
D
B
w = 3.99 kJ, ΔH = 0, ΔG = 2.38 kJ, ΔS surr = 13.3 J/K
ΔH° = 5.43 kJ
w = -2.94 kJ, ΔE = 27.8 kJ
ΔH° = 220.0 kJ, ΔS° = 809.0 J/K, ΔG° = -21.1 kJ
61.
62.
63.
64.
65.
66.
67.
68.
69.
70.
B
E
D
B
D
B
E
D
A
C
71.
72.
73.
74.
75.
76.
77.
78.
79.
80.
C
B
A
E
B
B
B
A
C
C
81.
82.
83.
84.
85.
86.
87.
88.
89.
90.
E
C
D
A
B
E
B
D
D
B
91.
92.
93.
94.
95.
96.
97.
98.
99.
100.
A
C
E
C
D
C
C
B
B
A