Question 1

The temperature at which the following process reaches equilibrium at 1.0 atm is the normal boiling point of hydrogen peroxide. H2O2(l)  2O2(l)    H2O2(g)  Use the following thermodynamic information at 298 K to determine this temperature. Substance: H2O2(l)  H2O2(g)  ΔH°f (kJ/mol) : -187.7 -136.3 ΔG°f (kJ/mol) : -120.4 -105.6 S°(J/K·mol) : 109.6 232.7 A)  120°C B)  144°C C)  196°C D)  418°C E)  585°C" class="answers-bank-image d-inline" rel="preload" > H2O2(g) 
Use the following thermodynamic information at 298 K to determine this temperature.
Substance: H2O2(l)  H2O2(g) 
ΔH°f (kJ/mol) : -187.7 -136.3
ΔG°f (kJ/mol) : -120.4 -105.6
S°(J/K·mol) : 109.6 232.7

Accepted Answer

A)   120°C
B)   144°C
C)   196°C
D)   418°C
E)   585°CF) B) and D)
G) B) and E)

Question 2

Consider the reaction CuI(s)  +(aq)  + I-(aq)  If the concentrations of the Cu+ and I- ions in equilibrium at 298 K are both equal to 1.03 × 10-6 M, what is the value of ΔG° for the reaction? A)  -68 kJ B)  68 kJ C)  -30. kJ D)  30 kJ E)  34 kJ" class="answers-bank-image d-inline" rel="preload" > Cu+(aq)  + I-(aq) 
If the concentrations of the Cu+ and I- ions in equilibrium at 298 K are both equal to 1.03 × 10-6 M, what is the value of ΔG° for the reaction?

Accepted Answer

A)   -68 kJ
B)   68 kJ
C)   -30. kJ
D)   30 kJ
E)   34 kJF) All of the above
G) B) and E)

Question 3

The free energy of a perfect crystal at absolute zero, is zero.

Accepted Answer

A) True 
 B)False

Question 4

Elemental boron can be formed by reaction of boron trichloride with hydrogen. BCl3(g)  + 1.5H2(g)  → B(s)  + 3HCl(g) 
Calculate ΔG° for the reaction.
Substance: BCl3(g)  H2(g)  B(s)  HCl(g) 
ΔG°f (kJ/mol) : -388.7 0 0 -95.3

Accepted Answer

A)   -293.4 kJ
B)   293.4 kJ
C)   -102.8 kJ
D)   102.8 kJ
E)   None of these choices are correct.F) A) and B)
G) C) and D)

Question 5

Calculate ΔG° for the reaction SiCl4(g)  + 2Mg(s)  → 2MgCl2(s)  + Si(s) 
Substance: SiCl4(g)  Mg(s)  MgCl2(s)  Si(s) 
ΔG°f (kJ/mol) : -616.98 0 -591.79 0

Accepted Answer

A)   566.60 kJ
B)   50.38 kJ
C)   25.19 kJ
D)   -25.19 kJ
E)   -566.60 kJF) A) and C)
G) None of the above

Question 6

Which relationship or statement best describes ΔS° for the following reaction? 2H2S(g)  + 3O2(g)  → 2H2O(g)  + 2SO2(g)

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) B) and D)
G) A) and C)

Question 7

Which one of the following phase changes decreases the entropy of the system?

Accepted Answer

A)   Melting
B)   Heating a gas
C)   Vaporization
D)   Condensation
E)   SublimationF) None of the above
G) C) and D)

Question 8

Which of the following is true for a system at equilibrium?

Accepted Answer

A)   ΔS°sys = ΔS°surr
B)   ΔS°sys = -ΔS°surr
C)   ΔS°sys = ΔS°surr = 0
D)   ΔS°univ > 0
E)   None of these choices are correct.F) A) and D)
G) A) and C)

Question 9

Calculate the equilibrium constant at 25°C for the reaction of methane with water to form carbon dioxide and hydrogen. The data refer to 25°C. CH4(g)  + 2H2O(g)  4(g)  + 2H2O(g)    CO2(g)  + 4H2(g)    A)  8.2 × 1019 B)  0.96 C)  0.58 D)  1.2 × 10-20 E)  1.4 × 10-46" class="answers-bank-image d-inline" rel="preload" > CO2(g)  + 4H2(g) 
4(g)  + 2H2O(g)    CO2(g)  + 4H2(g)    A)  8.2 × 1019 B)  0.96 C)  0.58 D)  1.2 × 10-20 E)  1.4 × 10-46" class="answers-bank-image d-inline" rel="preload" >

Accepted Answer

A)   8.2 × 1019
B)   0.96
C)   0.58
D)   1.2 × 10-20
E)   1.4 × 10-46F) B) and C)
G) A) and E)

Question 10

Which relationship best describes ΔS° for the following reaction? 8H2(g)  + S8(s)  → 8H2S(g)

Accepted Answer

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

Question 11

Which of the following values is based on the Third Law of Thermodynamics?

Accepted Answer

A)   ΔH°f = 0 for Al(s)  at 298 K
B)   ΔG°f = 0 for H2(g)  at 298 K
C)   S° = 51.446 J/(mol·K)  for Na(s)  at 298 K
D)   qsys 2O(l)  → H2O(s)  at 0°C
E)   None of these choices are correct.F) None of the above
G) C) and D)

Question 12

Which of the following results in a decrease in the entropy of the system?

Accepted Answer

A)   O2(g) , 300 K → O2(g) , 400 K
B)   H2O(s) , 0°C → H2O(l) , 0°C
C)   N2(g) , 25°C → N2(aq) , 25°C
D)   NH3(l) , -34.5°C → NH3(g) , -34.5°C
E)   2H2O2(g)  → 2H2O(g)  + O2(g) F) B) and C)
G) A) and B)

Question 13

Consider the figure that shows ΔG° for a chemical process plotted against absolute temperature.  0 B)  ΔS° > 0 C)  The reaction is spontaneous at high temperatures. D)  ΔS° increases with temperature while ΔH° remains constant. E)  There exists a certain temperature at which ΔH° = TΔS°." class="answers-bank-image d-inline" rel="preload" > Which one of the following is an incorrect conclusion, based on the information in the diagram?

Accepted Answer

A)   ΔH° > 0
B)   ΔS° > 0
C)   The reaction is spontaneous at high temperatures.
D)   ΔS° increases with temperature while ΔH° remains constant.
E)   There exists a certain temperature at which ΔH° = TΔS°.F) A) and E)
G) C) and E)

Question 14

Hydrogen sulfide decomposes according to the following reaction 2H2S(g)  → 2H2(g)  + S2(g) 
For this reaction at 298K ΔS° = 78.1 J/K, ΔH° = 169.4 kJ, and ΔG° = 146.1 kJ. What is the value of ΔG° at 900 K?

Accepted Answer

A)   -69881 kJ
B)   48.4 kJ
C)   99.1 kJ
D)   240 kJ
E)   441 kJF) C) and D)
G) All of the above

Question 15

For any reaction, if ΔG° > 0, then K < 1.

Accepted Answer

A) True 
 B)False

Question 16

Which of the following pairs has the member with the greater molar entropy listed first? All systems are at 25°C.

Accepted Answer

A)   CO(g) , CO2(g) 
B)   NaCl(s) , NaCl(aq) 
C)   H2S(g) , H2S(aq) 
D)   Li(s) , Pb(s) 
E)   H2(g) , H2O(g) F) B) and E)
G) C) and D)

Question 17

For a chemical reaction to be spontaneous at all 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)   It is not possible for a reaction to be spontaneous at all temperatures.F) A) and D)
G) All of the above

Question 18

Which, if any, of the following processes is spontaneous under the specified conditions?

Accepted Answer

A)   H2O(l)  → H2O(s)  at 25°C
B)   CO2(s)  → CO2(g)  at 0°C
C)   2H2O(g)  → 2H2(g)  + O2(g) 
D)   C(graphite)  → C(diamond)  at 25°C and 1 atm pressure
E)   None of these choices are correct.F) All of the above
G) A) and C)

Question 19

Which relationship or statement best describes ΔS° for the following reaction? HgS(s)  + O2(g)  → Hg(l)  + SO2(g)

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) B) and E)
G) B) and D)

Question 20

In 1774 Joseph Priestley prepared the element oxygen by heating mercury(II)  oxide: HgO(s)  → Hg(l)  + ½O2(g) 
For this reaction, ΔH° = 90.84 kJ and ΔS° = 108 J/K. Which of the following statements is true?

Accepted Answer

A)   The reaction is only spontaneous at low temperatures.
B)   The reaction is spontaneous at all temperatures.
C)   ΔG° becomes less favorable as the temperature is raised.
D)   The reaction is spontaneous only at high temperatures.
E)   The reaction is spontaneous under standard conditions at 25°C.F) B) and D)
G) D) and E)

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

Which of the following values is based on the Third Law of Thermodynamics?

Correct Answer
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Which, if any, of the following processes is spontaneous under the specified conditions?

Correct Answer
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Elemental boron can be formed by reaction of boron trichloride with hydrogen. BCl₃(g) + 1.5H₂(g) → B(s) + 3HCl(g) Calculate ΔG° for the reaction. Substance: BCl₃(g) H₂(g) B(s) HCl(g) ΔG°_f (kJ/mol) : -388.7 0 0 -95.3

Correct Answer
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Consider the figure that shows ΔG° for a chemical process plotted against absolute temperature. Which one of the following is an incorrect conclusion, based on the information in the diagram?

Correct Answer
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Which of the following is true for a system at equilibrium?

Correct Answer
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For any reaction, if ΔG° > 0, then K < 1.

Correct Answer
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Which of the following pairs has the member with the greater molar entropy listed first? All systems are at 25°C.

Correct Answer
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The free energy of a perfect crystal at absolute zero, is zero.

Correct Answer
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Which relationship or statement best describes ΔS° for the following reaction? 2H₂S(g) + 3O₂(g) → 2H₂O(g) + 2SO₂(g)

Correct Answer
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For a chemical reaction to be spontaneous at all temperatures, which of the following conditions must be met?

Correct Answer
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Hydrogen sulfide decomposes according to the following reaction 2H₂S(g) → 2H₂(g) + S₂(g) For this reaction at 298K ΔS° = 78.1 J/K, ΔH° = 169.4 kJ, and ΔG° = 146.1 kJ. What is the value of ΔG° at 900 K?

Correct Answer
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Consider the reaction CuI(s) Cu⁺(aq) + I^-(aq) If the concentrations of the Cu⁺ and I^- ions in equilibrium at 298 K are both equal to 1.03 × 10^-6 M, what is the value of ΔG° for the reaction?

Correct Answer
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Which relationship best describes ΔS° for the following reaction? 8H₂(g) + S₈(s) → 8H₂S(g)

Correct Answer
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Calculate the equilibrium constant at 25°C for the reaction of methane with water to form carbon dioxide and hydrogen. The data refer to 25°C. CH₄(g) + 2H₂O(g) CO₂(g) + 4H₂(g)

Correct Answer
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Correct Answer
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Which one of the following phase changes decreases the entropy of the system?

Correct Answer
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In 1774 Joseph Priestley prepared the element oxygen by heating mercury(II) oxide: HgO(s) → Hg(l) + ½O2(g) For this reaction, ΔH° = 90.84 kJ and ΔS° = 108 J/K. Which of the following statements is true?

Correct Answer
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Which relationship or statement best describes ΔS° for the following reaction? HgS(s) + O₂(g) → Hg(l) + SO₂(g)

Correct Answer
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Which of the following results in a decrease in the entropy of the system?

Correct Answer
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Calculate ΔG° for the reaction SiCl₄(g) + 2Mg(s) → 2MgCl₂(s) + Si(s) Substance: SiCl₄(g) Mg(s) MgCl₂(s) Si(s) ΔG°_f (kJ/mol) : -616.98 0 -591.79 0

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

Which of the following values is based on the Third Law of Thermodynamics?

Correct AnswerverifiedShow Answer

Which, if any, of the following processes is spontaneous under the specified conditions?

Correct AnswerverifiedShow Answer

Elemental boron can be formed by reaction of boron trichloride with hydrogen. BCl3(g) + 1.5H2(g) → B(s) + 3HCl(g) Calculate ΔG° for the reaction. Substance: BCl3(g) H2(g) B(s) HCl(g) ΔG°f (kJ/mol) : -388.7 0 0 -95.3

Correct AnswerverifiedShow Answer

Consider the figure that shows ΔG° for a chemical process plotted against absolute temperature. Which one of the following is an incorrect conclusion, based on the information in the diagram?

Correct AnswerverifiedShow Answer

Which of the following is true for a system at equilibrium?

Correct AnswerverifiedShow Answer

For any reaction, if ΔG° > 0, then K < 1.

Correct AnswerverifiedShow Answer

Which of the following pairs has the member with the greater molar entropy listed first? All systems are at 25°C.

Correct AnswerverifiedShow Answer

The free energy of a perfect crystal at absolute zero, is zero.

Correct AnswerverifiedShow Answer

Which relationship or statement best describes ΔS° for the following reaction? 2H2S(g) + 3O2(g) → 2H2O(g) + 2SO2(g)

Correct AnswerverifiedShow Answer

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

Correct AnswerverifiedShow Answer

Hydrogen sulfide decomposes according to the following reaction 2H2S(g) → 2H2(g) + S2(g) For this reaction at 298K ΔS° = 78.1 J/K, ΔH° = 169.4 kJ, and ΔG° = 146.1 kJ. What is the value of ΔG° at 900 K?

Correct AnswerverifiedShow Answer

Consider the reaction CuI(s) Cu+(aq) + I-(aq) If the concentrations of the Cu+ and I- ions in equilibrium at 298 K are both equal to 1.03 × 10-6 M, what is the value of ΔG° for the reaction?

Correct AnswerverifiedShow Answer

Which relationship best describes ΔS° for the following reaction? 8H2(g) + S8(s) → 8H2S(g)

Correct AnswerverifiedShow Answer

Calculate the equilibrium constant at 25°C for the reaction of methane with water to form carbon dioxide and hydrogen. The data refer to 25°C. CH4(g) + 2H2O(g) CO2(g) + 4H2(g)

Correct AnswerverifiedShow Answer

Correct AnswerverifiedShow Answer

Which one of the following phase changes decreases the entropy of the system?

Correct AnswerverifiedShow Answer

In 1774 Joseph Priestley prepared the element oxygen by heating mercury(II) oxide: HgO(s) → Hg(l) + ½O2(g) For this reaction, ΔH° = 90.84 kJ and ΔS° = 108 J/K. Which of the following statements is true?

Correct AnswerverifiedShow Answer

Which relationship or statement best describes ΔS° for the following reaction? HgS(s) + O2(g) → Hg(l) + SO2(g)

Correct AnswerverifiedShow Answer

Which of the following results in a decrease in the entropy of the system?

Correct AnswerverifiedShow Answer

Calculate ΔG° for the reaction SiCl4(g) + 2Mg(s) → 2MgCl2(s) + Si(s) Substance: SiCl4(g) Mg(s) MgCl2(s) Si(s) ΔG°f (kJ/mol) : -616.98 0 -591.79 0

Correct AnswerverifiedShow Answer

Correct Answer
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Correct Answer
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Elemental boron can be formed by reaction of boron trichloride with hydrogen. BCl₃(g) + 1.5H₂(g) → B(s) + 3HCl(g) Calculate ΔG° for the reaction. Substance: BCl₃(g) H₂(g) B(s) HCl(g) ΔG°_f (kJ/mol) : -388.7 0 0 -95.3

Correct Answer
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Correct Answer
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Correct Answer
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Correct Answer
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Correct Answer
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Correct Answer
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Which relationship or statement best describes ΔS° for the following reaction? 2H₂S(g) + 3O₂(g) → 2H₂O(g) + 2SO₂(g)

Correct Answer
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Correct Answer
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Hydrogen sulfide decomposes according to the following reaction 2H₂S(g) → 2H₂(g) + S₂(g) For this reaction at 298K ΔS° = 78.1 J/K, ΔH° = 169.4 kJ, and ΔG° = 146.1 kJ. What is the value of ΔG° at 900 K?

Correct Answer
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Consider the reaction CuI(s) Cu⁺(aq) + I^-(aq) If the concentrations of the Cu⁺ and I^- ions in equilibrium at 298 K are both equal to 1.03 × 10^-6 M, what is the value of ΔG° for the reaction?

Correct Answer
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Which relationship best describes ΔS° for the following reaction? 8H₂(g) + S₈(s) → 8H₂S(g)

Correct Answer
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Calculate the equilibrium constant at 25°C for the reaction of methane with water to form carbon dioxide and hydrogen. The data refer to 25°C. CH₄(g) + 2H₂O(g) CO₂(g) + 4H₂(g)

Correct Answer
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Correct Answer
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Correct Answer
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Which relationship or statement best describes ΔS° for the following reaction? HgS(s) + O₂(g) → Hg(l) + SO₂(g)

Correct Answer
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Correct Answer
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Calculate ΔG° for the reaction SiCl₄(g) + 2Mg(s) → 2MgCl₂(s) + Si(s) Substance: SiCl₄(g) Mg(s) MgCl₂(s) Si(s) ΔG°_f (kJ/mol) : -616.98 0 -591.79 0

Correct Answer
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