Question 1

Which of the following combinations of signs for ΔH and ΔS will always result in a reaction being nonspontaneous?

Accepted Answer

A)   ΔH+, ΔS-
B)   ΔH-, ΔS+
C)   ΔH-, ΔS-
D)   ΔH+, ΔS+
E)   cannot determine without temperature A

Question 2

Predict whether ΔS is positive or negative for the following process: H2O(g) → H2O(s)

Accepted Answer

A)   negative
B)   positive
C)   There is not enough information to determine.
D)   ΔS doesn't change.
E)   ΔS changes the same on both sides of the equation. A

Question 3

Predict whether ΔS is positive or negative for the following process: H2(g) + 1/2 O2(g) → H2O(g)

Accepted Answer

A)   negative
B)   positive
C)   There is not enough information to determine.
D)   ΔS doesn't change.
E)   ΔS changes the same on both sides of the equation. A

Question 4

Which of the following quantities is generally independent of temperature? I) ΔH
II) ΔS
III) ΔG

Accepted Answer

A)   I only
B)   II only
C)   III only
D)   I and II
E)   I, II, and III

Question 5

A spontaneous process:

Accepted Answer

A)   will happen quickly.
B)   releases large amounts of energy.
C)   requires an external action in order to begin reacting.
D)   will continue on its own once begun.
E)   is never endothermic.

Question 6

Consider the reaction: 
N2O4(g) → 2 NO2(g) Keq = 0.1134 at 20 °C. ΔH°rxn = 58.03 kJ/mol
What is ΔG° for this reaction at 20 °C?

Accepted Answer

A)   0.36 kJ
B)   -5.4 kJ
C)   4.9 kJ
D)   5.3 kJ
E)   5.4 kJ

Question 7

For CdO(s) + SO3(g) → CdSO4(s) ΔH° = -279.4 kJ/mol, and ΔS° = -118.4 J/mol-deg. What is ΔG° in kJ/mol at 127 K?

Accepted Answer

A)   -256 kJ/mol
B)   -303 kJ/mol
C)   -264 kJ/mol
D)   -355 kJ/mol
E)   -460 kJ/mol

Question 8

Consider the reaction:

What is ΔG°rxn for this reaction in kJ at 500 K?

Accepted Answer

A)   93 kJ
B)   151 kJ
C)   365 kJ
D)   -1.00 × 105 kJ
E)   441 kJ

Question 9

For the reaction, CO(g) + 2H2(g) → CH3OH(g)   &emsp; S° (J/mol K) 197.6 130.6 239.7
What is ΔS°rxn?

Accepted Answer

A)   -88.5 J/mol ∙ K
B)   -176.7 J/mol ∙ K
C)   219 J/mol ∙ K
D)   176.7 J/mol ∙ K
E)   -219.1 J/mol ∙ K

Question 10

Consider the endothermic reaction: N2(g) + O2(g) → 2 NO(g), ΔH° = 192.5 kJ/mol
At 2000 K the equilibrium constant is 5.0 × 10-4. At 2500 K the value of the equilibrium constant:

Accepted Answer

A)   is greater than 5.0 × 10-4
B)   depends on the concentration of oxygen
C)   is 10.0 × 10-4
D)   is 5.0 × 10-4
E)   is less than 5.0 × 10-4

Question 11

Consider the reaction: H2X(g) → HX(g) + X(g)
ΔH°rxn = 18.4 kJ/mol ΔS°rxn = 23.1 J/mol-K
What is Keq for this reaction at 525 K?

Accepted Answer

A)   0.387
B)   0.993
C)   0.238
D)   4.23
E)   1.01

Question 12

What is ΔG°rxn? 
CO(g) + 2 H2(g) → CH3OH(g)  &emsp; ΔGf° (J/mol K) -137.2 0   &emsp; -162.0

Accepted Answer

A)   -24.8 kJ
B)   -299.2 kJ
C)   +24.8 kJ
D)   149.6 kJ
E)   +299.2 kJ

Question 13

Indicate the statement(s) which are true for the process: Al+3(aq) + 3 OH-(aq) → Al(OH)3(s)
If it occurs in a closed container.
I. ΔS increases because the final molecule is more complicated.
II. Entropy decreases because the product is in the solid phase.
III. The two ions achieve a high degree of order as they crystalize, therefore ΔS is positive.
IV. Entropy of the system is unchanged because the system is sealed and at a constant temperature.

Accepted Answer

A)   I and II
B)   I and III
C)   II only
D)   I, II, IV
E)   I and IV

Question 14

The entropy of a pure perfect crystal at 25 K is zero.

Accepted Answer

A) True 
 B)False

Question 15

If a process is spontaneous, the reverse process is nonspontaneous.

Accepted Answer

A) True 
 B)False

Question 16

For the vaporization of water in an open system at 25°C and 1 atm, which of the following is correct?

Accepted Answer

A)   The reaction is entropy driven.
B)   The reaction is enthalpy driven.
C)   The reaction is not spontaneous.
D)   ΔG°rxn = 0

Question 17

For Cl2O(g) + 3/2 O2(g) → 2 ClO2 &emsp; &emsp; △H° = 126 kJ/mol, and ΔS° = -74.9 J/(mol∙deg) at 377°C. What is Keq?

Accepted Answer

A)   0.97
B)   6.12 × 10-7
C)   4.27 × 10-22
D)   9.17 × 10-15
E)   1.07 × 1014

Question 18

For an exothermic reaction to be nonspontaneous at high temperatures, the enthalpy must be ________ while the entropy is ________.

Accepted Answer

A)   positive, also positive
B)   positive, negative
C)   a relatively small negative value, also negative
D)   a relatively large negative value, positive
E)   a very large negative value, also negative

Question 19

What is ΔH° for a reaction that has Kp = 1.456 at 273 K and Kp = 14.2 at 298 K?

Accepted Answer

A)   8.42 × 10-5 kJ/mol
B)   61.6 kJ/mol
C)   -61.6 kJ/mol
D)   462 kJ/mol
E)   -462 kJ/mol

Question 20

What is ΔG°rxn? 
&emsp; &emsp; CaCO3(s) → CaO(s) + CO2(g)
ΔGf° -1128 &emsp;&emsp;&emsp;-604&emsp;&emsp; -394.4
(J/mol K)

Accepted Answer

A)   1338 kJ
B)   918 kJ
C)   -130 kJ
D)   -918 kJ
E)   130 kJ

Exam 19: Spontaneous Change: Entropy and Free Energy

Which of the following combinations of signs for ΔH and ΔS will always result in a reaction being nonspontaneous?

Predict whether ΔS is positive or negative for the following process: H₂O(g) → H₂O(s)

Predict whether ΔS is positive or negative for the following process: H₂(g) + 1/2 O₂(g) → H₂O(g)

Which of the following quantities is generally independent of temperature? I) ΔH II) ΔS III) ΔG

A spontaneous process:

Consider the reaction: N₂O₄(g) → 2 NO₂(g) Keq = 0.1134 at 20 °C. ΔH°rxn = 58.03 kJ/mol What is ΔG° for this reaction at 20 °C?

For CdO(s) + SO₃(g) → CdSO₄(s) ΔH° = -279.4 kJ/mol, and ΔS° = -118.4 J/mol-deg. What is ΔG° in kJ/mol at 127 K?

Consider the reaction: What is ΔG°rxn for this reaction in kJ at 500 K?

For the reaction, CO(g) + 2H₂(g) → CH₃OH(g) S° (J/mol K) 197.6 130.6 239.7 What is ΔS°rxn?

Consider the endothermic reaction: N₂(g) + O₂(g) → 2 NO(g) , ΔH° = 192.5 kJ/mol At 2000 K the equilibrium constant is 5.0 × 10^-4. At 2500 K the value of the equilibrium constant:

Consider the reaction: H₂X(g) → HX(g) + X(g) ΔH°rxn = 18.4 kJ/mol ΔS°rxn = 23.1 J/mol-K What is Keq for this reaction at 525 K?

What is ΔG°rxn? CO(g) + 2 H₂(g) → CH₃OH(g) ΔGf° (J/mol K) -137.2 0 -162.0

The entropy of a pure perfect crystal at 25 K is zero.

If a process is spontaneous, the reverse process is nonspontaneous.

For the vaporization of water in an open system at 25°C and 1 atm, which of the following is correct?

For Cl₂O(g) + 3/2 O₂(g) → 2 ClO₂ △H° = 126 kJ/mol, and ΔS° = -74.9 J/(mol∙deg) at 377°C. What is Keq?

For an exothermic reaction to be nonspontaneous at high temperatures, the enthalpy must be while the entropy is .

What is ΔH° for a reaction that has Kp = 1.456 at 273 K and Kp = 14.2 at 298 K?

What is ΔG°rxn? CaCO₃(s) → CaO(s) + CO₂(g) ΔGf° -1128 -604 -394.4 (J/mol K)

Exam 19: Spontaneous Change: Entropy and Free Energy

Which of the following combinations of signs for ΔH and ΔS will always result in a reaction being nonspontaneous?

Predict whether ΔS is positive or negative for the following process: H2O(g) → H2O(s)

Predict whether ΔS is positive or negative for the following process: H2(g) + 1/2 O2(g) → H2O(g)

Which of the following quantities is generally independent of temperature? I) ΔH II) ΔS III) ΔG

A spontaneous process:

Consider the reaction: N2O4(g) → 2 NO2(g) Keq = 0.1134 at 20 °C. ΔH°rxn = 58.03 kJ/mol What is ΔG° for this reaction at 20 °C?

For CdO(s) + SO3(g) → CdSO4(s) ΔH° = -279.4 kJ/mol, and ΔS° = -118.4 J/mol-deg. What is ΔG° in kJ/mol at 127 K?

Consider the reaction: What is ΔG°rxn for this reaction in kJ at 500 K?

For the reaction, CO(g) + 2H2(g) → CH3OH(g) S° (J/mol K) 197.6 130.6 239.7 What is ΔS°rxn?

Consider the endothermic reaction: N2(g) + O2(g) → 2 NO(g) , ΔH° = 192.5 kJ/mol At 2000 K the equilibrium constant is 5.0 × 10-4. At 2500 K the value of the equilibrium constant:

Consider the reaction: H2X(g) → HX(g) + X(g) ΔH°rxn = 18.4 kJ/mol ΔS°rxn = 23.1 J/mol-K What is Keq for this reaction at 525 K?

What is ΔG°rxn? CO(g) + 2 H2(g) → CH3OH(g) ΔGf° (J/mol K) -137.2 0 -162.0

The entropy of a pure perfect crystal at 25 K is zero.

If a process is spontaneous, the reverse process is nonspontaneous.

For the vaporization of water in an open system at 25°C and 1 atm, which of the following is correct?

For Cl2O(g) + 3/2 O2(g) → 2 ClO2 △H° = 126 kJ/mol, and ΔS° = -74.9 J/(mol∙deg) at 377°C. What is Keq?

For an exothermic reaction to be nonspontaneous at high temperatures, the enthalpy must be ________ while the entropy is ________.

What is ΔH° for a reaction that has Kp = 1.456 at 273 K and Kp = 14.2 at 298 K?

What is ΔG°rxn? CaCO3(s) → CaO(s) + CO2(g) ΔGf° -1128 -604 -394.4 (J/mol K)

Predict whether ΔS is positive or negative for the following process: H₂O(g) → H₂O(s)

Predict whether ΔS is positive or negative for the following process: H₂(g) + 1/2 O₂(g) → H₂O(g)

Consider the reaction: N₂O₄(g) → 2 NO₂(g) Keq = 0.1134 at 20 °C. ΔH°rxn = 58.03 kJ/mol What is ΔG° for this reaction at 20 °C?

For CdO(s) + SO₃(g) → CdSO₄(s) ΔH° = -279.4 kJ/mol, and ΔS° = -118.4 J/mol-deg. What is ΔG° in kJ/mol at 127 K?

For the reaction, CO(g) + 2H₂(g) → CH₃OH(g) S° (J/mol K) 197.6 130.6 239.7 What is ΔS°rxn?

Consider the endothermic reaction: N₂(g) + O₂(g) → 2 NO(g) , ΔH° = 192.5 kJ/mol At 2000 K the equilibrium constant is 5.0 × 10^-4. At 2500 K the value of the equilibrium constant:

Consider the reaction: H₂X(g) → HX(g) + X(g) ΔH°rxn = 18.4 kJ/mol ΔS°rxn = 23.1 J/mol-K What is Keq for this reaction at 525 K?

What is ΔG°rxn? CO(g) + 2 H₂(g) → CH₃OH(g) ΔGf° (J/mol K) -137.2 0 -162.0

For Cl₂O(g) + 3/2 O₂(g) → 2 ClO₂ △H° = 126 kJ/mol, and ΔS° = -74.9 J/(mol∙deg) at 377°C. What is Keq?

For an exothermic reaction to be nonspontaneous at high temperatures, the enthalpy must be while the entropy is .

What is ΔG°rxn? CaCO₃(s) → CaO(s) + CO₂(g) ΔGf° -1128 -604 -394.4 (J/mol K)