Question 1

Which of the following best expresses the increased degree of randomness associated with melting and sublimation, respectively?

Accepted Answer

A)  ΔSfus - ΔSsub = 0 
B)  ΔSfus = 144.3 J/mol-K, ΔSsub = 9.0 J/mol-K 
C)  ΔSfus = 9.0 J/mol-K, ΔSsub = -144.3 J/mol-K 
D)  ΔH for both processes is zero 
E)  ΔSfus = 9.0 J/mol-K, ΔSsub = 144.3 J/mol-K 
A)  ΔSfus - ΔSsub = 0 
B)  ΔSfus = 144.3 J/mol-K, ΔSsub = 9.0 J/mol-K 
C)  ΔSfus = 9.0 J/mol-K, ΔSsub = -144.3 J/mol-K 
D)  ΔH for both processes is zero 
E)  ΔSfus = 9.0 J/mol-K, ΔSsub = 144.3 J/mol-K

Question 2

Calculate the entropy change for methanol at its normal boiling point of 64.5°C. ΔH° = 38.0 kJ/mol.

Accepted Answer

A)  0.589 kJ/mol ∙ K 
B)  0.112 kJ/mol ∙ K 
C)  589 kJ/mol ∙ K 
D)  112 kJ/mol ∙ K 
E)  0.589 × 10-2 kJ/mol ∙ K 
A)  0.589 kJ/mol ∙ K 
B)  0.112 kJ/mol ∙ K 
C)  589 kJ/mol ∙ K 
D)  112 kJ/mol ∙ K 
E)  0.589 × 10-2 kJ/mol ∙ K

Question 3

The equilibrium constant for the reaction below is 7.2 x 10-4 at 298 K and 1 atm. HNO2(aq) + H2O(l) ⇌ NO2-(aq) + H3O+(aq)
When [HNO2(aq)] = 1.0 M and [NO2-(aq)] = [H3O+(aq)] = 1.0 x 10-5 M, calculate ΔG.

Accepted Answer

A)  -39.1 kJ/mol 
B)  +17.9 kJ/mol 
C)  -17.9 kJ/mol 
D)  +39.1 kJ/mol 
A)  -39.1 kJ/mol 
B)  +17.9 kJ/mol 
C)  -17.9 kJ/mol 
D)  +39.1 kJ/mol

Question 4

Which of the following statements are true? 
I. Liquids have more entropy than their solids.
II. Solutions have more entropy than the solids dissolved.
III. Gases and their liquids have equal entropy.
IV. Gases have less entropy than their solids.
V. Entropy of a substance increases as its temperature increases.

Accepted Answer

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

Question 5

Order the following by increasing entropy. CO(g), COCl2(g), CO2(g), CaO(s)

Accepted Answer

A)  CO2 2 
B)  CaO 2 2 
C)  COCl2 2 
D)  CO2 2 2 2 
A)  CO2 2 
B)  CaO 2 2 
C)  COCl2 2 
D)  CO2 2 2 2

Question 6

A nonspontaneous reaction can be made to occur by coupling it with a spontaneous reaction to form an overall spontaneous reaction.

Accepted Answer

A) True 
 B)False

Question 7

For the reaction PCl5(g) → PCl3(g) + Cl2(g) at 298 K, Keq = 1.87 × 10-7, ΔS° = 181.92 J/mol K. Compute ΔH° for this reaction.

Accepted Answer

A)  15.8 kJ/mol 
B)  220 kJ/mol 
C)  143 kJ/mol 
D)  54.2 kJ/mol 
E)  92.6 kJ/mol 
A)  15.8 kJ/mol 
B)  220 kJ/mol 
C)  143 kJ/mol 
D)  54.2 kJ/mol 
E)  92.6 kJ/mol

Question 8

Consider the following reaction. 
   &emsp; &emsp;S2Cl2(g) + 2 OCl2(g) → 2 SOCl2(g) + Cl2(g)
ΔG°f  &emsp; -32   &emsp;  &emsp;97.9     &emsp;&emsp;  &emsp;-320   &emsp;    &emsp;&emsp;0.0 kJ/mol
What is ΔG° for this reaction in kJ?

Accepted Answer

A)  -804 
B)  -476 
C)  -386 
D)  -413 
E)  -799 
A)  -804 
B)  -476 
C)  -386 
D)  -413 
E)  -799

Question 9

What is ΔG° at 25°C? 
CO(g) + 2 H2(g) → CH3OH(g)   &emsp; ΔH° = -90.7 kJ  &emsp;  ΔS° = -221 J/K

Accepted Answer

A)  -90.9 kJ 
B)  -24.8 kJ 
C)  -156.6 kJ 
D)  -96.2 kJ 
E)  -85.2 kJ 
A)  -90.9 kJ 
B)  -24.8 kJ 
C)  -156.6 kJ 
D)  -96.2 kJ 
E)  -85.2 kJ

Question 10

What is ΔG° at 25°C? N2O4(g) → 2 NO2(g) ΔH° = 58.03 kJ  &emsp;  ΔS° = 176.7 J/K

Accepted Answer

A)  58.21 kJ 
B)  62.45 kJ 
C)  53.6 kJ 
D)  5.37 kJ 
E)  111 kJ 
A)  58.21 kJ 
B)  62.45 kJ 
C)  53.6 kJ 
D)  5.37 kJ 
E)  111 kJ

Question 11

For the reaction I2(s) + Cl2(g) → 2 ICl(g)   &emsp; ΔH = 36 kJ and ΔS = 158.8 J/K at 25°C. Calculate the temperature at which Keq is 4.0 × 103.

Accepted Answer

A)  128 °C 
B)  -115 °C 
C)  83 °C 
D)  25 °C 
E)  -175 °C 
A)  128 °C 
B)  -115 °C 
C)  83 °C 
D)  25 °C 
E)  -175 °C

Question 12

The maximum quantity of energy available for useful work is:

Accepted Answer

A)  constant 
B)  Gibbs energy 
C)  the entropy 
D)  the internal energy 
E)  the enthalpy 
A)  constant 
B)  Gibbs energy 
C)  the entropy 
D)  the internal energy 
E)  the enthalpy

Question 13

Consider the following reaction: 
4 NH3(g) + 7 O2(g) → 4 NO2(g) + 6 H2O (l)  &emsp; ΔG°f   &emsp; -16.7  &emsp;  0.0  &emsp;  51.8   &emsp; -237.2 kJ/mol
What is Keq for this reaction at 25 °C?

Accepted Answer

A)  e-464 
B)  e464 
C)  1.59 
D)  0.63 
E)  252 
A)  e-464 
B)  e464 
C)  1.59 
D)  0.63 
E)  252

Question 14

For the reaction PCl5(g) → PCl3(g) + Cl2(g) at 298 K, Keq = 1.87 × 10-7, ΔS° = 181.92 J/mol K, what is Keq at 200 K if ΔH° = 92.6 kJ/mol?

Accepted Answer

A)  2.08 × 10-15 
B)  16.8 
C)  1.87 × 10-7 
D)  5.35 × 106 
E)  5.95 × 10-2 
A)  2.08 × 10-15 
B)  16.8 
C)  1.87 × 10-7 
D)  5.35 × 106 
E)  5.95 × 10-2

Question 15

Predict whether ΔS is positive or negative for the following process: 2 Cl2O7(g) → 2 Cl2(g) + 7 O2(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)  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.

Question 16

Consider the following reaction:
 4 NH3(g) + 7 O2(g) → 4 NO2(g) + 6 H2O (l)  &emsp;  ΔG°f   &emsp; -16.7   &emsp; 0.0   &emsp; 51.8   &emsp; -237.2 kJ/mol
What is ΔG° for this reaction in kJ?

Accepted Answer

A)  -1282 
B)  -1149 
C)  -169 
D)  169 
E)  1149 
A)  -1282 
B)  -1149 
C)  -169 
D)  169 
E)  1149

Question 17

The following reaction is endothermic. 2NH3(g) → N2(g) + 3H2(g)
This means the reaction:

Accepted Answer

A)  will be spontaneous at high temperature 
B)  will be spontaneous at low temperature 
C)  is not spontaneous at any temperature 
D)  is spontaneous at all temperatures 
A)  will be spontaneous at high temperature 
B)  will be spontaneous at low temperature 
C)  is not spontaneous at any temperature 
D)  is spontaneous at all temperatures

Question 18

The change in Gibbs energy of a reaction:

Accepted Answer

A)  = work 
B)  predicts speed 
C)  = ΔH + TΔS 
D)  depends on the standard state chosen 
E)  tells us if the reaction is spontaneous or not 
A)  = work 
B)  predicts speed 
C)  = ΔH + TΔS 
D)  depends on the standard state chosen 
E)  tells us if the reaction is spontaneous or not

Question 19

Choose the INCORRECT statement about coupled reactions.

Accepted Answer

A)  The usual practice of coupling reactions is to join two nonspontaneous reactions. 
B)  The usual reason to couple reactions is to produce an overall spontaneous reaction. 
C)  The reaction added to a nonspontaneous reaction needs to be spontaneous. 
D)  The reaction added to a nonspontaneous reaction needs to be more spontaneous than the original reaction is nonspontaneous. 
E)  One of the coupled reactions has a negative ΔG, the other a positive ΔG. 
A)  The usual practice of coupling reactions is to join two nonspontaneous reactions. 
B)  The usual reason to couple reactions is to produce an overall spontaneous reaction. 
C)  The reaction added to a nonspontaneous reaction needs to be spontaneous. 
D)  The reaction added to a nonspontaneous reaction needs to be more spontaneous than the original reaction is nonspontaneous. 
E)  One of the coupled reactions has a negative ΔG, the other a positive ΔG.

Question 20

Calculate ΔG° for the reaction Cu(s) + H2O(g) → CuO(s) + H2(g) at 500K.

Accepted Answer

A)  231.8 kJ 
B)  -135.4 kJ 
C)  -58.6 kJ 
D)  110.6 kJ 
E)  86.74 kJ 
A)  231.8 kJ 
B)  -135.4 kJ 
C)  -58.6 kJ 
D)  110.6 kJ 
E)  86.74 kJ

Exam 19: Spontaneous Change: Entropy and Free Energy

Which of the following best expresses the increased degree of randomness associated with melting and sublimation, respectively?

Calculate the entropy change for methanol at its normal boiling point of 64.5°C. ΔH° = 38.0 kJ/mol.

The equilibrium constant for the reaction below is 7.2 x 10-4 at 298 K and 1 atm. HNO2(aq) + H2O(l) ⇌ NO2-(aq) + H3O+(aq) When [HNO2(aq)] = 1.0 M and [NO2-(aq)] = [H3O+(aq)] = 1.0 x 10-5 M, calculate ΔG.

Order the following by increasing entropy. CO(g), COCl2(g), CO2(g), CaO(s)

A nonspontaneous reaction can be made to occur by coupling it with a spontaneous reaction to form an overall spontaneous reaction.

For the reaction PCl5(g) → PCl3(g) + Cl2(g) at 298 K, Keq = 1.87 × 10-7, ΔS° = 181.92 J/mol K. Compute ΔH° for this reaction.

Consider the following reaction. S2Cl2(g) + 2 OCl2(g) → 2 SOCl2(g) + Cl2(g) ΔG°f -32 97.9 -320 0.0 kJ/mol What is ΔG° for this reaction in kJ?

What is ΔG° at 25°C? CO(g) + 2 H2(g) → CH3OH(g) ΔH° = -90.7 kJ ΔS° = -221 J/K

What is ΔG° at 25°C? N2O4(g) → 2 NO2(g) ΔH° = 58.03 kJ ΔS° = 176.7 J/K

For the reaction I2(s) + Cl2(g) → 2 ICl(g) ΔH = 36 kJ and ΔS = 158.8 J/K at 25°C. Calculate the temperature at which Keq is 4.0 × 103.

The maximum quantity of energy available for useful work is:

Consider the following reaction: 4 NH3(g) + 7 O2(g) → 4 NO2(g) + 6 H2O (l) ΔG°f -16.7 0.0 51.8 -237.2 kJ/mol What is Keq for this reaction at 25 °C?

For the reaction PCl5(g) → PCl3(g) + Cl2(g) at 298 K, Keq = 1.87 × 10-7, ΔS° = 181.92 J/mol K, what is Keq at 200 K if ΔH° = 92.6 kJ/mol?

Predict whether ΔS is positive or negative for the following process: 2 Cl2O7(g) → 2 Cl2(g) + 7 O2(g)

Consider the following reaction: 4 NH3(g) + 7 O2(g) → 4 NO2(g) + 6 H2O (l) ΔG°f -16.7 0.0 51.8 -237.2 kJ/mol What is ΔG° for this reaction in kJ?

The following reaction is endothermic. 2NH3(g) → N2(g) + 3H2(g) This means the reaction:

The change in Gibbs energy of a reaction:

Choose the INCORRECT statement about coupled reactions.

Calculate ΔG° for the reaction Cu(s) + H2O(g) → CuO(s) + H2(g) at 500K.

Matter - Its Properties and Measurement

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Introduction to Reactions in Aqueous Solutions

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The equilibrium constant for the reaction below is 7.2 x 10^-4 at 298 K and 1 atm. HNO₂(aq) + H₂O(l) ⇌ NO₂^-(aq) + H₃O⁺(aq) When [HNO₂(aq)] = 1.0 M and [NO₂^-(aq)] = [H₃O⁺(aq)] = 1.0 x 10^-5 M, calculate ΔG.

Order the following by increasing entropy. CO(g), COCl₂(g), CO₂(g), CaO(s)

For the reaction PCl₅(g) → PCl₃(g) + Cl₂(g) at 298 K, Keq = 1.87 × 10^-7, ΔS° = 181.92 J/mol K. Compute ΔH° for this reaction.

Consider the following reaction. S₂Cl₂(g) + 2 OCl₂(g) → 2 SOCl₂(g) + Cl₂(g) ΔG°f -32 97.9 -320 0.0 kJ/mol What is ΔG° for this reaction in kJ?

What is ΔG° at 25°C? CO(g) + 2 H₂(g) → CH₃OH(g) ΔH° = -90.7 kJ ΔS° = -221 J/K

What is ΔG° at 25°C? N₂O₄(g) → 2 NO₂(g) ΔH° = 58.03 kJ ΔS° = 176.7 J/K

For the reaction I₂(s) + Cl₂(g) → 2 ICl(g) ΔH = 36 kJ and ΔS = 158.8 J/K at 25°C. Calculate the temperature at which Keq is 4.0 × 10³.

Consider the following reaction: 4 NH₃(g) + 7 O₂(g) → 4 NO₂(g) + 6 H₂O (l) ΔG°f -16.7 0.0 51.8 -237.2 kJ/mol What is Keq for this reaction at 25 °C?

For the reaction PCl₅(g) → PCl₃(g) + Cl₂(g) at 298 K, Keq = 1.87 × 10^-7, ΔS° = 181.92 J/mol K, what is Keq at 200 K if ΔH° = 92.6 kJ/mol?

Predict whether ΔS is positive or negative for the following process: 2 Cl₂O₇(g) → 2 Cl₂(g) + 7 O₂(g)

Consider the following reaction: 4 NH₃(g) + 7 O₂(g) → 4 NO₂(g) + 6 H₂O (l) ΔG°f -16.7 0.0 51.8 -237.2 kJ/mol What is ΔG° for this reaction in kJ?

The following reaction is endothermic. 2NH₃(g) → N₂(g) + 3H₂(g) This means the reaction:

Calculate ΔG° for the reaction Cu(s) + H₂O(g) → CuO(s) + H₂(g) at 500K.