Chapter 17: Spontaneity, Entropy, and Free Energy
1. For which process is S negative?
A)
evaporation of 1 mol of CCl4(l)
B)
mixing 5 mL ethanol with 25 mL water
C)
compressing 1 mol Ne at constant temperature from 1.5 L to 0.5 L
D)
raising the temperature of 100 g Cu from 275 K to 295 K
E)
grinding a large crystal of KCl to powder
2. Ten identical coins are shaken vigorously in a cup and then poured out onto a table top.
Which of the following distributions has the highest probability of occurrence? (T = Tails,
H = Heads)
A)
T10H0
B)
T8H2
C)
T7H3
D)
T5H5
E)
T4H6
3. If two pyramid-shaped dice (with numbers 1 through 4 on the sides) were tossed, which
outcome has the highest entropy?
A)
The sum of the dice is 3.
B)
The sum of the dice is 4.
C)
The sum of the dice is 5.
D)
The sum of the dice is 6.
E)
The sum of the dice is 7.
4. A two-bulbed flask contains 5 particles. What is the probability of finding all 5 particles on
the left side?
A)
2.50%
B)
2.24%
C)
3.13%
D)
0.20%
E)
6.25%
5. Which of the following shows a decrease in entropy?
A)
precipitation
B)
gaseous reactants forming a liquid
C)
a burning piece of wood
D)
melting ice
E)
two of these
6. Which of the following result(s) in an increase in the entropy of the system?
I.
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)
I
B)
II, V
C)
I, III, IV
D)
I, II, III, IV
E)
I, II, III, V
7. Consider the following processes:
I.
II
III.
IV.
For how many of these is S positive?
A)
0
B)
1
C)
2
D)
3
E)
4
8. The second law of thermodynamics states that:
A)
The entropy of a perfect crystal is zero at 0 K.
B)
The entropy of the universe is constant.
C)
The energy of the universe is increasing.
D)
The entropy of the universe is increasing.
E)
The energy of the universe is constant.
9. Which of the following statements is true?
A)
The total energy and entropy of the universe are both increasing.
B)
The total energy of the universe is increasing, but the entropy is constant.
C)
The total energy of the universe increases, while the entropy decreases.
D)
The total energy of the universe is constant, but the entropy is increasing.
E)
None of these.
10. 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. For
the dissolving of the solid
A)
H < 0
B)
Suniv > 0
C)
Ssys< 0
D)
Ssurr > 0
E)
none of these
11. A chemical reaction is most likely to be spontaneous if it is accompanied by
A)
increasing energy and increasing entropy
B)
lowering energy and increasing entropy
C)
increasing energy and decreasing entropy
D)
lowering energy and decreasing entropy
E)
none of these (A-D)
12. 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 one mole of ice at 0°C is melted by heat supplied from
surroundings at 276 K, what is the entropy change in the surroundings, in J/K?
A)
22.1
B)
21.8
C)
0.0
D)
–21.8
E)
–22.1
13. If the change in entropy of the surroundings for a process at 431 K and constant pressure is
–326 J/K, what is the heat flow absorbed by for the system?
A)
326 kJ
B)
1.32 kJ
C)
–141 kJ
D)
105 kJ
E)
141 kJ
14. The heat of vaporization for 1.0 mole of water at 100.°C and 1.0 atm is 40.56 kJ/mol.
Calculate S for the process H2O(l) → H2O(g) at 100.°C.
A)
109 J/K mol
B)
–109 J/K mol
C)
406 J/K mol
D)
–406 J/K mol
E)
none of these
15. A change of state that occurs in a system is accompanied by 52.3 kJ of heat, which is
transferred to the surroundings at a constant pressure and a constant temperature of 300. K.
For this process Ssurr is:
A)
52.3 kJ/K
B)
–52.3 kJ/K
C)
–174 J/K
D)
174 J/K
E)
248 kJ/K
16. he enthalpy of vaporization of ammonia is 23.35 kJ/mol at its boiling point (–33.4°C).
Calculate the value of Ssurr when 1.00 mole of ammonia is vaporized at –33.4°C and 1.00
atm.
A)
0
B)
–6.99 102 J/K mol
C)
9.74 101 J/K mol
D)
–9.74 101 J/K mol
E)
6.99 102 J/K mol
17. Ssurr is _______ for exothermic reactions and ______ for endothermic reactions.
A)
favorable, unfavorable
B)
unfavorable, favorable
C)
favorable, favorable
D)
unfavorable, unfavorable
E)
cannot tell
18. Which of the following is true for exothermic processes?
A)
Ssurr < 0
B)
Ssurr = –H/T
C)
Ssurr = 0
D)
Ssurr > 0
E)
two of these
19. Ssurr for this process is
A)
greater than zero
B)
less than zero
C)
equal to zero
D)
more information needed to answer this question
E)
none of these (A-D)
20. Ssys for this process is
A)
greater than zero
B)
less than zero
C)
equal to zero
D)
more information needed to answer this question
E)
none of these (A-D)
21. Suniv for this process is
A)
greater than zero
B)
less than zero
C)
equal to zero
D)
more information needed to answer this question
E)
none of these (A-D)
22. Given that Hvap is 58.2 kJ/mol, and the boiling point is 83.4°C, 1 atm, if one mole of this
substance is vaporized at 1 atm, calculate Ssurr.
A)
–163 J/K mol
B)
163 J/K mol
C)
698 J/K mol
D)
–698 J/K mol
E)
0
23. As long as the disorder of the surroundings is increasing, a process will be spontaneous.
24. For any given process, Ssurr and Ssys have opposite signs.
25. If Ssurr = –Ssys, the process is at equilibrium.
26. Which of the following is true?
A)
By spontaneous we mean that the reaction or process will always proceed to the
right (as written) even if very slowly. Increasing the temperature may speed up the
reaction, but it does not affect the spontaneity of the reaction.
B)
By spontaneous we mean that the reaction or process will always proceed to the
left (as written) even if very slowly. Increasing the temperature may speed up the
reaction, but it does not affect the spontaneity of the reaction.
C)
By spontaneous we mean that the reaction or process will always proceed to the
left (as written) even if very slowly. Increasing the temperature may speed up the
reaction and it generally affects the spontaneity of the reaction.
D)
By spontaneous we mean that the reaction or process will always proceed to the
right (as written) even if very slowly. Increasing the temperature may speed up the
reaction, and it generally affects the spontaneity of the reaction.
E)
None of the above is true.
27. Substance X has a heat of vaporization of 55.9 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 Suniv.
A)
0
B)
80.3 J/K mol
C)
132 J/K mol
D)
–80.3 J/K mol
E)
–132 J/K mol
28. Substance X has a heat of vaporization of 58.4 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 Ssurr.
A)
0
B)
83.9 J/K mol
C)
138 J/K mol
D)
–83.9 J/K mol
E)
–138 J/K mol
29. Substance X has a heat of vaporization of 47.1 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 S.
A)
0
B)
67.7 J/K mol
C)
111 J/K mol
D)
–67.7 J/K mol
E)
–111 J/K mol
30. Substance X has a heat of vaporization of 64.4 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 G.
A)
0 J
B)
92.5 J
C)
152 J
D)
–92.5 J
E)
–152 J
31. he enthalpy of vaporization of ammonia is 23.35 kJ/mol at its boiling point (–33.4°C).
Calculate the value of S when 1.00 mole of ammonia is vaporized at –33.4°C and 1.00
atm.
A)
0
B)
–6.99 102 J/K mol
C)
9.74 101 J/K mol
D)
–9.74 101 J/K mol
E)
6.99 102 J/K mol
32. S is _______ for exothermic reactions and ______ for endothermic reactions.
A)
favorable, unfavorable
B)
unfavorable, favorable
C)
favorable, favorable
D)
unfavorable, unfavorable
E)
cannot tell
33. For the process CHCl3(s) → CHCl3(l), H° = 9.19 kJ/mol and S° = 43.9 J/mol/K. What is
the melting point of chloroform?
A)
–64 °C
B)
209 °C
C)
130 °C
D)
64 °C
E)
–130 °C
34. Given that Hvap is 60.3 kJ/mol, and the boiling point is 83.4°C, 1 atm, if one mole of this
substance is vaporized at 1 atm, calculate S.
A)
–169 J/K mol
B)
169 J/K mol
C)
723 J/K mol
D)
–723 J/K mol
E)
0
35. H° is zero for a chemical reaction at constant temperature.
Consider two perfectly insulated vessels. Vessel #1 initially contains an ice cube at 0°C and
water at 0°C. Vessel #2 initially contains an ice cube at 0°C and a saltwater solution at 0°C.
In each vessel, consider the “system” to be the ice, and the “surroundings” to be the liquid.
36. Determine the sign of Ssys, Ssurr, and Suniv for the contents of
Vessel #1.
Ssys
Ssurr
Suniv
A)
0 0 0
B)
+ – 0
C)
+ + +
D)
+ – +
E)
+ 0 +
37. Determine the sign of Ssys, Ssurr, and Suniv for the system (ice/saltwater) in
Vessel #2.
Ssys
Ssurr
Suniv
A)
0 0 0
B)
+ – 0
C)
+ + +
D)
+ – +
E)
+ 0 +
38. The melting point of water is 0°C at 1 atm pressure because under these conditions:
A)
S for the process H2O(s) → H2O(l) is positive.
B)
S and Ssurr for the process H2O(s) → H2O(l) are both positive.
C)
S and Ssurr for the process H2O(s) → H2O(l) are equal in magnitude and opposite
in sign.
D)
G is positive for the process H2O(s) → H2O(l).
E)
None of these is correct.
39. 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).
E)
None of these (A-D).
40. Which of the following statements is always true for a spontaneous process?
I.
Ssys > 0
II.
Ssurr > 0
III.
Suniv > 0
IV.
Gsys > 0
A)
I
B)
III
C)
IV
D)
I and III
E)
III and IV
41. For a spontaneous exothermic process, which of the following must be true?
A)
G must be positive.
B)
S must be positive.
C)
S must be negative.
D)
Two of the above must be true.
E)
None of the above (A-C) must be true.
42. 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
Which of the following is consistent with this information?
A)
The reactants are thermodynamically more stable than the products.
B)
The reaction has a small equilibrium constant.
C)
The ultraviolet light raises the temperature of the system and makes the reaction
more favorable.
D)
The negative value for S slows down the reaction.
E)
The reaction is spontaneous, but the reactants are kinetically stable.
43. For a particular chemical reaction H = 4.3 kJ and S = –19 J/K. Under what temperature
condition is the reaction spontaneous?
A)
When T < –226 K.
B)
When T < 226 K.
C)
The reaction is spontaneous at all temperatures.
D)
The reaction is not spontaneous at any temperature.
E)
When T > 226 K.
44. For a certain process at 355 K, G = –11.8 kJ and H = –9.2 kJ. Therefore, S for the
process is
A)
0 J/K mol
B)
7.3 J/K mol
C)
–7.3 J/K mol
D)
–25.9 J/K mol
E)
25.9 J/K mol
45. Consider the freezing of liquid water at –10°C. For this process what are the signs for H,
S, and G?
H
S
G
A)
+ – 0
B)
+ – –
C)
– + 0
D)
– + –
E)
– – –
46. For the process of a certain liquid vaporizing at 1 atm, H°vap = 54.2 kJ/mol and
S°vap= 74.1 J/mol K. Assuming these values are independent of T, what is the normal
boiling point of this liquid?
A)
731 °C
B)
1004 °C
C)
458 °C
D)
0.731 °C
E)
none of these
47. 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
48. 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.
49. For the process S8 (rhombic) → S8 (monoclinic) at 110°C, H = 3.21 kJ/mol and
S = 8.70 J/K mol (at 110°C).
Which of the following is correct?
A)
This reaction is spontaneous at 110°C (S8 (monoclinic) is stable).
B)
This reaction is spontaneous at 110°C (S8 (rhombic) is stable).
C)
This reaction is nonspontaneous at 110°C (S8 (rhombic) is stable).
D)
This reaction is nonspontaneous at 110°C (S8 (monoclinic) is stable).
E)
Need more data.
50. 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 –743.07 J/mol, and S for the same transition
is -17.0 J/K mol. At what temperature are Solids I and II in equilibrium?
A)
13.6 K
B)
43.7 K
C)
19.8 K
D)
98.2 K
E)
They can never be in equilibrium because they are both solids.
51. At constant pressure, the following reaction 2NO2(g) → N2O4(g) is exothermic. The
reaction (as written) is
A)
always spontaneous
B)
spontaneous at low temperatures, but not high temperatures
C)
spontaneous at high temperatures, but not low temperatures
D)
never spontaneous
E)
cannot tell
52. Given that Hvap is 53.3 kJ/mol, and the boiling point is 83.4°C, 1 atm, if one mole of this
substance is vaporized at 1 atm, calculate G.
A)
–150 J
B)
150 J
C)
639 J
D)
–639 J
E)
0 J
The following questions refer to the following reaction at constant 25°C and 1 atm.
2Fe(s) + (3/2)O2(g) + 3H2O(l) → 2Fe(OH)3(s) H = –789 kJ/mol
Substance
S° (J/mol K)
Fe(OH)3(s)
107
Fe(s)
27
O2(g)
205
H2O(l)
70
53. Determine Ssurr for the reaction (in kJ/mol K)
A)
3.14
B)
0.937
C)
0.378
D)
1.31
E)
2.65
54. Determine Suniv for the reaction (in kJ/mol K)
A)
0.23
B)
2.3
C)
0.36
D)
2.8
E)
3.6
55. What must be true about G for this reaction?
A)
G = H
B)
G = 0
C)
G > 0
D)
G < 0
E)
G = Suniv
56. Given the following data, calculate the normal boiling point for formic acid (HCOOH).
Hf°(kJ/mol)
S°(J/mol K)
HCOOH(l)
-410.
130.0
HCOOH(g)
-363
251.1
A)
0.39 °C
B)
388 °C
C)
661 °C
D)
279 °C
E)
115 °C
57. The following reaction takes place at 120°C: H2O(l) → H2O(g) H = 44.0 kJ/mol
S = 0.119 kJ/mol K
Which of the following must be true?
A)
The reaction is not spontaneous.
B)
The reaction is spontaneous.
C)
G = 0
D)
G < 0
E)
Two of these.
When ignited, solid ammonium dichromate decomposes in a fiery display. This is the
reaction for a “volcano” demonstration. The decomposition produces nitrogen gas, water
vapor, and chromium(III) oxide. The temperature is constant at 25°C.
Substance
Hf° (kJ/mol)
S° (kJ/mol K)
Cr2O3(g)
–1147
0.08118
H2O(l)
–242
0.1187
N2(g)
0
0.1915
(NH4)2Cr2O7(s)
–22.5
0.1137
58. Determine Suniv° (in kJ/mol K).
A)
7.66
B)
6.39
C)
84.3
D)
5.22
E)
6.03
59. Determine S° reaction (in kJ/mol K).
A)
0.2777
B)
0.8612
C)
0.7475
D)
0.6338
E)
0.1590
60. Determine G° (in kJ/mol).
A)
–191.4
B)
–2281.4
C)
–38.9
D)
1903.6
E)
–1555.4
61. The third law of thermodynamics states:
A)
The entropy of the universe is increasing.
B)
The entropy of the universe is constant.
C)
The entropy is zero at 0 K for a perfect crystal.
D)
The absolute entropy of a substance decreases with increasing temperature.
E)
The entropy of the universe equals the sum of the entropy of system and
surroundings.
62. 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)
63. Which of the following statements is (are) always true?
I.
In order for a process to be spontaneous, the entropy of the universe must
increase.
II.
A system cannot have both energy disorder and positional disorder.
III.
Suniv =
IV.
S° is zero for elements in their standard states.
A)
I
B)
I, IV
C)
I, III, IV
D)
II, IV
E)
II
64. In which process is S expected to be positive?
A)
a reaction that forms a solid precipitant from aqueous solutions
B)
an ideal gas being compressed at a constant temperature and against a constant
pressure
C)
water freezing below its normal freezing point
D)
a spontaneous endothermic process at a constant temperature and pressure
E)
none of these
65. In which reaction is S° expected to be positive?
A)
I2(g) → I2(s)
B)
H2O(l) → H2O(s)
C)
CH3OH(g) + O2(g) → CO2(g) + 2H2O(l)
D)
2O2(g) + 2SO(g) → 2SO3(g)
E)
none of these
66. For the dissociation reaction of the acid HF:
HF(aq) H+(aq) + F–(aq)
S is observed to be negative. The best explanation is:
A)
This is the expected result since each HF molecule produces two ions when it
dissociates.
B)
Hydration of the ions produces the negative value of S.
C)
The reaction is expected to be exothermic and thus S should be negative.
D)
The reaction is expected to be endothermic and thus S should be negative.
E)
None of these can explain the negative value of S.
67. Consider the dissociation of hydrogen:
H2(g) 2H(g)
One would expect that this reaction:
A)
will be spontaneous at any temperature
B)
will be spontaneous at high temperatures
C)
will be spontaneous at low temperatures
D)
will not be spontaneous at any temperature
E)
will never happen
68. When a stable diatomic molecule spontaneously forms from its atoms, what are the signs of
H°, S°, and G°?
H
S
G