Question 1

Which of the following is always true for an exothermic process?

Accepted Answer

A)   qsys > 0, ΔSsurr 
B)   qsys surr > 0
C)   qsys surr 
D)   qsys > 0, ΔSsurr > 0
E)   w < 0F) All of the above
G) B) and C)

Question 2

Nitric oxide reacts with chlorine to form NOCl. The data refer to 298 K. 2NO(g)  + Cl2(g)  → 2NOCl(g) 
Substance: NO(g)  Cl2(g)  NOCl(g) 
ΔH°f (kJ/mol) : 90.29 0 51.71
ΔG°f (kJ/mol) : 86.60 0 66.07
S°(J/K·mol) : 210.65 223.0 261.6
What is the value of ΔG° for this reaction at 550 K?

Accepted Answer

A)   -143.76 kJ
B)   -78.78 kJ
C)   -22.24 kJ
D)   -10.56 kJ
E)   66600 kJF) A) and E)
G) A) and D)

Question 3

A certain process has ΔH° > 0, ΔS°  0. The values of ΔH° and ΔS° do not depend on the temperature. Which of the following is a correct conclusion about this process?

Accepted Answer

A)   It is non-spontaneous at all T.
B)   It is spontaneous at high T.
C)   It is spontaneous at low T.
D)   It is spontaneous at all T.
E)   None of these choices are correct.F) C) and D)
G) B) and D)

Question 4

For a chemical reaction to be non-spontaneous at any temperature, which of the following conditions must be met?

Accepted Answer

A)   ΔS° > 0, ΔH° > 0
B)   ΔS° > 0, ΔH° 
C)   ΔS° 
D)   ΔS°  0
E)   All reactions are spontaneous at some temperature.F) A) and E)
G) A) and B)

Question 5

Calculate ΔS° for the reaction SiCl4(g)  + 2Mg(s)  → 2MgCl2(s)  + Si(s) 
Substance: SiCl4(g)  Mg(s)  MgCl2(s)  Si(s) 
S°(J/K·mol) : 330.73 32.68 89.62 18.83

Accepted Answer

A)   -254.96 J/K
B)   -198.02 J/K
C)   198.02 J/K
D)   254.96 J/K
E)   471.86 J/KF) C) and E)
G) A) and D)

Question 6

Which one of the following changes of state increases the entropy of the system?

Accepted Answer

A)   Condensation
B)   Cooling a gas
C)   Freezing
D)   Crystallization
E)   SublimationF) C) and D)
G) B) and E)

Question 7

You are given pure samples of ethane, C2H6(g) , and toluene, C7H8(l) . What prediction would you make concerning their standard molar entropies at 298 K?

Accepted Answer

A)   S°ethane > S°toluene
B)   S°ethane toluene
C)   S°ethane ≈ (S°toluene)  ÷ 3
D)   S°ethane ≈ S°toluene
E)   Since toluene is much more complex than ethane, but ethane is in the gas phase while toluene is a liquid, any of these predictions can be confidently made without further information or calculations.F) B) and C)
G) A) and E)

Question 8

Which relationship best describes ΔS° for the following reaction? CO(g)  + H2O(g)  → CO2(g)  + H2(g)

Accepted Answer

A)   ΔS° = ΔH°
B)   ΔS° = ΔH°/T
C)   ΔS° > 0
D)   ΔS° 
E)   ΔS° ≈ 0F) A) and B)
G) C) and E)

Question 9

Use the given data at 298 K to calculate ΔG° for the reaction 2Cl2(g)  + SO2(g)  → SOCl2(g)  + Cl2O(g) 
Substance: Cl2(g)  SO2(g)  SOCl2 (g)  Cl2O(g) 
ΔH°f (kJ/mol) : 0 -296.8 -212.5 80.3
S°(J/K·mol) : 223.0 248.1 309.77 266.1

Accepted Answer

A)   129.3 kJ
B)   133.6 kJ
C)   196.0 kJ
D)   199.8 kJ
E)   229.6 kJF) D) and E)
G) B) and E)

Question 10

Which of the following conditions will ensure that a chemical reaction will definitely proceed in the forward direction, toward products?

Accepted Answer

A)   ΔH > 0
B)   ΔH 
C)   ΔSsys > 0
D)   ΔSsurr > ΔSsys
E)   ΔS > ΔH/TF) All of the above
G) A) and C)

Question 11

Which of the following is always true for an endothermic process?

Accepted Answer

A)   qsys > 0, ΔSsurr 
B)   qsys surr > 0
C)   qsys surr 
D)   qsys > 0, ΔSsurr > 0
E)   w < 0F) A) and B)
G) C) and D)

Question 12

Use the thermodynamic data at 298 K below to determine the Ksp for barium carbonate, BaCO3 at this temperature. Substance: Ba2+(aq)  CO32-(aq)  BaCO3(s) 
ΔH°f (kJ/mol) : -538.36 -676.26 -1219
ΔG°f (kJ/mol) : -560.7 -528.1 -1139
S°(J/K·mol) : 13 -53.1 112

Accepted Answer

A)   5.86
B)   6.30 × 108
C)   1.59 × 10-9
D)   5.47 × 10-21
E)   2.18 × 10-27F) A) and C)
G) A) and E)

Question 13

A certain process has ΔSuniv > 0 at 25°C. What does one know about the process?

Accepted Answer

A)   It is exothermic.
B)   It is endothermic.
C)   It is spontaneous at 25°C.
D)   It will move rapidly toward equilibrium.
E)   None of these choices are correct.F) C) and D)
G) D) and E)

Question 14

Consider the figure that shows ΔG° for a chemical process plotted against absolute temperature. From this plot, it is reasonable to conclude that  0, ΔS° > 0 B)  ΔH° > 0, ΔS°  0 D)  ΔH°

Accepted Answer

A)   ΔH° > 0, ΔS° > 0
B)   ΔH° > 0, ΔS° 
C)   ΔH°  0
D)   ΔH° 
E)   None of these choices are correct.F) C) and D)
G) A) and E)

Question 15

The entropy of one mole of oxygen gas in a 0.5-L container is less than it would be in a 22.4-L container at the same temperature.

Accepted Answer

A) True 
 B)False

Question 16

When a sky diver free-falls through the air, the process is

Accepted Answer

A)   non-spontaneous because he is accelerating due to the force applied by gravity.
B)   non-spontaneous because he is losing potential energy.
C)   non-spontaneous, if he had planned the jump for two weeks.
D)   spontaneous.
E)   in equilibrium.F) A) and B)
G) D) and E)

Question 17

Which relationship or statement best describes ΔS° for the following reaction? KCl(s)  → K+(aq)  + Cl-(aq)

Accepted Answer

A)   ΔS° ≈ 0
B)   ΔS° 
C)   ΔS° > 0
D)   ΔS° = ΔH°/T
E)   More information is needed to make a reasonable prediction.F) A) and B)
G) B) and E)

Question 18

Which of the following is necessary for a process to be spontaneous?

Accepted Answer

A)   ΔHsys 
B)   ΔSsys > 0
C)   ΔSsurr 
D)   ΔSuniv > 0
E)   ΔGsys = 0F) B) and C)
G) C) and E)

Question 19

You are given pure samples of pentane, CH3CH2CH2CH2CH3(l) , and 1,3-pentadiene, CH2=CHCH=CHCH3(l) . What prediction would you make concerning their standard molar entropies at 298 K?

Accepted Answer

A)   S°pentane > S°1, 3-pentadiene
B)   S°pentane pentadiene
C)   S°pentane ≈ S°1, 3-pentadiene
D)   S°pentane = S°1, 3-pentadiene + 2 S°H2
E)   More information is needed to make reasonable predictions.F) B) and E)
G) C) and E)

Question 20

For a chemical reaction to be spontaneous only at low temperatures, which of the following conditions must be met?

Accepted Answer

A)   ΔS° > 0, ΔH° > 0
B)   ΔS° > 0, ΔH° 
C)   ΔS° 
D)   ΔS°  0
E)   ΔG° > 0F) A) and E)
G) A) and D)

Exam 20: Thermodynamics Entropy, Free Energy, and Reaction Direction

Consider the figure that shows ΔG° for a chemical process plotted against absolute temperature. From this plot, it is reasonable to conclude that

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Which of the following conditions will ensure that a chemical reaction will definitely proceed in the forward direction, toward products?

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When a sky diver free-falls through the air, the process is

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Nitric oxide reacts with chlorine to form NOCl. The data refer to 298 K. 2NO(g) + Cl2(g) → 2NOCl(g) Substance: NO(g) Cl2(g) NOCl(g) ΔH°f (kJ/mol) : 90.29 0 51.71 ΔG°f (kJ/mol) : 86.60 0 66.07 S°(J/K·mol) : 210.65 223.0 261.6 What is the value of ΔG° for this reaction at 550 K?

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You are given pure samples of pentane, CH3CH2CH2CH2CH3(l) , and 1,3-pentadiene, CH2=CHCH=CHCH3(l) . What prediction would you make concerning their standard molar entropies at 298 K?

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Calculate ΔS° for the reaction SiCl4(g) + 2Mg(s) → 2MgCl2(s) + Si(s) Substance: SiCl4(g) Mg(s) MgCl2(s) Si(s) S°(J/K·mol) : 330.73 32.68 89.62 18.83

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Which of the following is always true for an exothermic process?

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Which of the following is necessary for a process to be spontaneous?

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Which one of the following changes of state increases the entropy of the system?

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For a chemical reaction to be non-spontaneous at any temperature, which of the following conditions must be met?

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Which of the following is always true for an endothermic process?

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Use the given data at 298 K to calculate ΔG° for the reaction 2Cl2(g) + SO2(g) → SOCl2(g) + Cl2O(g) Substance: Cl2(g) SO2(g) SOCl2 (g) Cl2O(g) ΔH°f (kJ/mol) : 0 -296.8 -212.5 80.3 S°(J/K·mol) : 223.0 248.1 309.77 266.1

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The entropy of one mole of oxygen gas in a 0.5-L container is less than it would be in a 22.4-L container at the same temperature.

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A certain process has ΔSuniv > 0 at 25°C. What does one know about the process?

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Which relationship best describes ΔS° for the following reaction? CO(g) + H2O(g) → CO2(g) + H2(g)

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You are given pure samples of ethane, C2H6(g) , and toluene, C7H8(l) . What prediction would you make concerning their standard molar entropies at 298 K?

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For a chemical reaction to be spontaneous only at low temperatures, which of the following conditions must be met?

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Use the thermodynamic data at 298 K below to determine the Ksp for barium carbonate, BaCO3 at this temperature. Substance: Ba2+(aq) CO32-(aq) BaCO3(s) ΔH°f (kJ/mol) : -538.36 -676.26 -1219 ΔG°f (kJ/mol) : -560.7 -528.1 -1139 S°(J/K·mol) : 13 -53.1 112

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A certain process has ΔH° > 0, ΔS° < 0, and ΔG° > 0. The values of ΔH° and ΔS° do not depend on the temperature. Which of the following is a correct conclusion about this process?

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Which relationship or statement best describes ΔS° for the following reaction? KCl(s) → K+(aq) + Cl-(aq)

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Nitric oxide reacts with chlorine to form NOCl. The data refer to 298 K. 2NO(g) + Cl₂(g) → 2NOCl(g) Substance: NO(g) Cl₂(g) NOCl(g) ΔH°_f (kJ/mol) : 90.29 0 51.71 ΔG°_f (kJ/mol) : 86.60 0 66.07 S°(J/K·mol) : 210.65 223.0 261.6 What is the value of ΔG° for this reaction at 550 K?

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You are given pure samples of pentane, CH₃CH₂CH₂CH₂CH₃(l) , and 1,3-pentadiene, CH₂=CHCH=CHCH₃(l) . What prediction would you make concerning their standard molar entropies at 298 K?

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Calculate ΔS° for the reaction SiCl₄(g) + 2Mg(s) → 2MgCl₂(s) + Si(s) Substance: SiCl4(g) Mg(s) MgCl₂(s) Si(s) S°(J/K·mol) : 330.73 32.68 89.62 18.83

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Use the given data at 298 K to calculate ΔG° for the reaction 2Cl₂(g) + SO₂(g) → SOCl₂(g) + Cl₂O(g) Substance: Cl₂(g) SO₂(g) SOCl₂ (g) Cl₂O(g) ΔH°_f (kJ/mol) : 0 -296.8 -212.5 80.3 S°(J/K·mol) : 223.0 248.1 309.77 266.1

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A certain process has ΔS_univ > 0 at 25°C. What does one know about the process?

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Which relationship best describes ΔS° for the following reaction? CO(g) + H₂O(g) → CO₂(g) + H₂(g)

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You are given pure samples of ethane, C₂H₆(g) , and toluene, C₇H₈(l) . What prediction would you make concerning their standard molar entropies at 298 K?

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Use the thermodynamic data at 298 K below to determine the K_sp for barium carbonate, BaCO₃ at this temperature. Substance: Ba²⁺(aq) CO₃^2-(aq) BaCO₃(s) ΔH°f (kJ/mol) : -538.36 -676.26 -1219 ΔG°f (kJ/mol) : -560.7 -528.1 -1139 S°(J/K·mol) : 13 -53.1 112

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Which relationship or statement best describes ΔS° for the following reaction? KCl(s) → K⁺(aq) + Cl^-(aq)

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