Question 1

Which of the listed reactions would couple with the following reaction to produce silver? Ag2O(s) → 2 Ag(s) + 1/2 O(g)   &emsp;   &emsp; ΔG° = 11.2 kJ/mol

Accepted Answer

A)  Ag(s) + 1/2 Br2 → AgBr(s)   &emsp;   &emsp; ΔG° = 96.9 kJ/mol 
B)  C + 1/2 O2 → CO   &emsp;   &emsp; ΔG° = -137.2 kJ/mol 
C)  N + 1/2 O2 → NO   &emsp;   &emsp; ΔG° = 149.3 kJ/mol 
D)  N + O2 → NO2 ΔG° = 51.3 kJ/mol 
E)  C + 2 S → CS2(l)   &emsp;   &emsp; ΔG° = 65.3 kJ/mol 
A)  Ag(s) + 1/2 Br2 → AgBr(s)   &emsp;   &emsp; ΔG° = 96.9 kJ/mol 
B)  C + 1/2 O2 → CO   &emsp;   &emsp; ΔG° = -137.2 kJ/mol 
C)  N + 1/2 O2 → NO   &emsp;   &emsp; ΔG° = 149.3 kJ/mol 
D)  N + O2 → NO2 ΔG° = 51.3 kJ/mol 
E)  C + 2 S → CS2(l)   &emsp;   &emsp; ΔG° = 65.3 kJ/mol

Question 2

A spontaneous reaction is one that must have a negative value of ΔH.

Accepted Answer

A) True 
 B)False

Question 3

If the vapor pressure of water in an open system at 25°C is 23.8 mmHg, what is ΔG for the reaction below at 25°C? H2O(l) → H2O(g, 23.8 mmHg)

Accepted Answer

A)  0 kJ/mol 
B)  -8.58 kJ/mol 
C)  +8.58 kJ/mol 
D)  -0.720 kJ/mol 
A)  0 kJ/mol 
B)  -8.58 kJ/mol 
C)  +8.58 kJ/mol 
D)  -0.720 kJ/mol

Question 4

What is ΔG° at 25°C? 
CO2(g) → CO2(aq) &emsp; ΔH° = -19.4 kJ &emsp; ΔS° = 92.3 J/K

Accepted Answer

A)  2.1 kJ 
B)  -46.9 kJ 
C)  -17.1 kJ 
D)  -19.5 kJ 
E)  -21.7 kJ 
A)  2.1 kJ 
B)  -46.9 kJ 
C)  -17.1 kJ 
D)  -19.5 kJ 
E)  -21.7 kJ

Question 5

If ΔG is positive for a certain reaction, then:

Accepted Answer

A)  the reaction is spontaneous. 
B)  the reverse of the reaction is spontaneous. 
C)  the system is in equilibrium. 
D)  one would need to know the Kelvin temperature to determine spontaneity. 
E)  there would be no reaction possible for a negative value. 
A)  the reaction is spontaneous. 
B)  the reverse of the reaction is spontaneous. 
C)  the system is in equilibrium. 
D)  one would need to know the Kelvin temperature to determine spontaneity. 
E)  there would be no reaction possible for a negative value.

Question 6

Which of the following relations is true for the molar entropy of sublimation of a substance?

Accepted Answer

A)  ΔSsub = ΔSfusion + ΔSvaporization 
B)  ΔSsub < ΔSvaporization 
C)  ΔSsub = ΔSfusion - ΔSvaporization 
D)  ΔSsub < (ΔSfusion + ΔSvaporization) 
A)  ΔSsub = ΔSfusion + ΔSvaporization 
B)  ΔSsub < ΔSvaporization 
C)  ΔSsub = ΔSfusion - ΔSvaporization 
D)  ΔSsub < (ΔSfusion + ΔSvaporization)

Question 7

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

Accepted Answer

A)  77.8 
B)  51.4 
C)  98.3 
D)  175 
E)  129.2 
A)  77.8 
B)  51.4 
C)  98.3 
D)  175 
E)  129.2

Question 8

For CO(g) + H2(g) → H2CO(g)   &emsp; ΔH° = -5.36 kJ/mol, and ΔS° = -109.8 J/mol-deg. What is the temperature at which Keq is 1.0 × 10-2?

Accepted Answer

A)  5.19 × 103 °C 
B)  218 °C 
C)  25 °C 
D)  -198 °C 
E)  -237 °C 
A)  5.19 × 103 °C 
B)  218 °C 
C)  25 °C 
D)  -198 °C 
E)  -237 °C

Question 9

For the reaction,
 N2O4(g) → 2 NO2(g) S° (J/mol K) 
 &emsp; 304.2   &emsp;   &emsp; 240.0
What is ΔS°rxn?

Accepted Answer

A)  544.2 J/mol ∙ K 
B)  -64.2 J/mol ∙ K 
C)  175.8 J/mol ∙ K 
D)  -175.8 J/mol ∙ K 
E)  64.2 J/mol ∙ K 
A)  544.2 J/mol ∙ K 
B)  -64.2 J/mol ∙ K 
C)  175.8 J/mol ∙ K 
D)  -175.8 J/mol ∙ K 
E)  64.2 J/mol ∙ K

Question 10

Consider the reaction: 
  &emsp;   &emsp; N2(g) + 3 X2(g) → 2 NX3(g)
△H°  &emsp;  0.0  &emsp;  0.0     &emsp; &emsp; -43 kJ/mol
S°   &emsp; 192  &emsp;   &emsp;  210   &emsp; &emsp; 172 J/(mol∙K)
What is Keq for this reaction at 591 K?

Accepted Answer

A)  2.3 × 1017 
B)  4.3 × 10-18 
C)  1.04 
D)  0.96 
E)  132 
A)  2.3 × 1017 
B)  4.3 × 10-18 
C)  1.04 
D)  0.96 
E)  132

Question 11

Nonspontaneous reactions and spontaneous reactions cannot be coupled.

Accepted Answer

A) True 
 B)False

Question 12

Consider the following reaction: 
  &emsp;NH3(g) + HCl(g) → NH4Cl(s)
S° 192.51   &emsp;186.69   &emsp;94.56 J/mol∙deg
What is ΔS° for this reaction in J/mol∙deg?

Accepted Answer

A)  -284.6 J/mol∙deg 
B)  284.6 J/mol∙deg 
C)  -92.3 J/mol∙deg 
D)  94.6 J/mol∙deg 
E)  92.3 J/mol∙deg 
A)  -284.6 J/mol∙deg 
B)  284.6 J/mol∙deg 
C)  -92.3 J/mol∙deg 
D)  94.6 J/mol∙deg 
E)  92.3 J/mol∙deg

Question 13

For the reaction I2(s) + Cl2(g) → 2 ICl(g)   &emsp; ΔH = 36 kJ and ΔS = 158.8 J/K at 25 °C. Calculate ΔG for the process at 25 °C.

Accepted Answer

A)  -11.3 kJ 
B)  -4730 kJ 
C)  -393 kJ 
D)  32 kJ 
E)  83.3 kJ 
A)  -11.3 kJ 
B)  -4730 kJ 
C)  -393 kJ 
D)  32 kJ 
E)  83.3 kJ

Question 14

The following reaction is exothermic. 2N2O(g) → 2N2(g) + O2(g)
This means the reaction:

Accepted Answer

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

Question 15

A zero ΔG means the system is at equilibrium.

Accepted Answer

A) True 
 B)False

Question 16

Choose the INCORRECT statement.

Accepted Answer

A)  The third law of thermodynamics states that the entropy of a pure crystal at 298 K is zero. 
B)  ΔS° = Σ (ν S°) products - Σ (ν S°) reactants. 
C)  The activity of pure liquids or pure solids is 1. 
D)  ΔG° = -RT ln Keq. 
E)  ΔG° = ΔH° - TΔS°. 
A)  The third law of thermodynamics states that the entropy of a pure crystal at 298 K is zero. 
B)  ΔS° = Σ (ν S°) products - Σ (ν S°) reactants. 
C)  The activity of pure liquids or pure solids is 1. 
D)  ΔG° = -RT ln Keq. 
E)  ΔG° = ΔH° - TΔS°.

Question 17

Which material has the largest entropy?

Accepted Answer

A)  cannot be determined 
B)  pure water 
C)  powdered sugar 
D)  salt water 
E)  crystalline salt 
A)  cannot be determined 
B)  pure water 
C)  powdered sugar 
D)  salt water 
E)  crystalline salt

Question 18

For the reaction, 2 O3(g) → 3 O2(g)
S° (J/mol K) 238.8 205.0
What is ΔS°rxn?

Accepted Answer

A)  137.4 J/mol K 
B)  -137.4 J/mol K 
C)  33.8 J/mol K 
D)  171.2 J/mol K 
E)  -33.8 J/mol K 
A)  137.4 J/mol K 
B)  -137.4 J/mol K 
C)  33.8 J/mol K 
D)  171.2 J/mol K 
E)  -33.8 J/mol K

Question 19

Consider the reaction: AB(g) → A(g) + B(g) (Keq = 0.729 at 20°C ΔH° = 45.9 kJ/mol)
What is Keq for this reaction at 377 K?

Accepted Answer

A)  45.9 
B)  191 
C)  91.2 
D)  66.6 
E)  48.5 
A)  45.9 
B)  191 
C)  91.2 
D)  66.6 
E)  48.5

Question 20

Choose the INCORRECT statement.

Accepted Answer

A)  The van't Hoff equation is ln   =
  . 
B)  Keq is independent of temperature. 
C)  In a thermodynamic equilibrium constant expression, the activity of a gas is replaced by its partial pressure in atmosphere. 
D)  In a Keq expression, the activity of a solution is replaced by its molarity. 
E)  If ΔG = 0, the process is at equilibrium. 
A)  The van't Hoff equation is ln   =
  . 
B)  Keq is independent of temperature. 
C)  In a thermodynamic equilibrium constant expression, the activity of a gas is replaced by its partial pressure in atmosphere. 
D)  In a Keq expression, the activity of a solution is replaced by its molarity. 
E)  If ΔG = 0, the process is at equilibrium.

Exam 19: Spontaneous Change: Entropy and Free Energy

Which of the listed reactions would couple with the following reaction to produce silver? Ag2O(s) → 2 Ag(s) + 1/2 O(g) ΔG° = 11.2 kJ/mol

A spontaneous reaction is one that must have a negative value of ΔH.

If the vapor pressure of water in an open system at 25°C is 23.8 mmHg, what is ΔG for the reaction below at 25°C? H2O(l) → H2O(g, 23.8 mmHg)

What is ΔG° at 25°C? CO2(g) → CO2(aq) ΔH° = -19.4 kJ ΔS° = 92.3 J/K

If ΔG is positive for a certain reaction, then:

Which of the following relations is true for the molar entropy of sublimation of a substance?

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

For CO(g) + H2(g) → H2CO(g) ΔH° = -5.36 kJ/mol, and ΔS° = -109.8 J/mol-deg. What is the temperature at which Keq is 1.0 × 10-2?

For the reaction, N2O4(g) → 2 NO2(g) S° (J/mol K) 304.2 240.0 What is ΔS°rxn?

Consider the reaction: N2(g) + 3 X2(g) → 2 NX3(g) △H° 0.0 0.0 -43 kJ/mol S° 192 210 172 J/(mol∙K) What is Keq for this reaction at 591 K?

Nonspontaneous reactions and spontaneous reactions cannot be coupled.

Consider the following reaction: NH3(g) + HCl(g) → NH4Cl(s) S° 192.51 186.69 94.56 J/mol∙deg What is ΔS° for this reaction in J/mol∙deg?

For the reaction I2(s) + Cl2(g) → 2 ICl(g) ΔH = 36 kJ and ΔS = 158.8 J/K at 25 °C. Calculate ΔG for the process at 25 °C.

The following reaction is exothermic. 2N2O(g) → 2N2(g) + O2(g) This means the reaction:

A zero ΔG means the system is at equilibrium.

Choose the INCORRECT statement.

Which material has the largest entropy?

For the reaction, 2 O3(g) → 3 O2(g) S° (J/mol K) 238.8 205.0 What is ΔS°rxn?

Consider the reaction: AB(g) → A(g) + B(g) (Keq = 0.729 at 20°C ΔH° = 45.9 kJ/mol) What is Keq for this reaction at 377 K?

Choose the INCORRECT statement.

Matter - Its Properties and Measurement

Atoms and the Atomic Theory

Chemical Compounds

Chemical Reactions

Introduction to Reactions in Aqueous Solutions

Gases

Thermochemistry

Electrons in Atoms

The Periodic Table and Some Atomic Properties

Chemical Bonding I: Basic Concepts

Chemical Bonding II: Additional Aspects

Intermolecular Forces: Liquids and Solids

Solutions and Their Physical Properties

Chemical Kinetics

Principles of Chemical Equilibrium

Acids and Bases

Additional Aspects of Acid-Base Equilibria

Solubility and Complex-Ion Equilibria

Electrochemistry

Main Group Elements I: Groups 1, 2, 13, and 14

Main Group Elements II: Groups 18, 17, 16, 15, and Hydrogen

The Transition Elements

Complex Ions and Coordination Compounds

Nuclear Chemistry 1-41

Structures of Organic Compounds

Reactions of Organic Compounds

Chemistry of the Living State

Filters

Which of the listed reactions would couple with the following reaction to produce silver? Ag₂O(s) → 2 Ag(s) + 1/2 O(g) ΔG° = 11.2 kJ/mol

If the vapor pressure of water in an open system at 25°C is 23.8 mmHg, what is ΔG for the reaction below at 25°C? H₂O(l) → H₂O(g, 23.8 mmHg)

What is ΔG° at 25°C? CO₂(g) → CO₂(aq) ΔH° = -19.4 kJ ΔS° = 92.3 J/K

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

For CO(g) + H₂(g) → H₂CO(g) ΔH° = -5.36 kJ/mol, and ΔS° = -109.8 J/mol-deg. What is the temperature at which Keq is 1.0 × 10^-2?

For the reaction, N₂O₄(g) → 2 NO₂(g) S° (J/mol K) 304.2 240.0 What is ΔS°rxn?

Consider the reaction: N₂(g) + 3 X₂(g) → 2 NX₃(g) △H° 0.0 0.0 -43 kJ/mol S° 192 210 172 J/(mol∙K) What is Keq for this reaction at 591 K?

Consider the following reaction: NH₃(g) + HCl(g) → NH₄Cl(s) S° 192.51 186.69 94.56 J/mol∙deg What is ΔS° for this reaction in J/mol∙deg?

For the reaction I₂(s) + Cl₂(g) → 2 ICl(g) ΔH = 36 kJ and ΔS = 158.8 J/K at 25 °C. Calculate ΔG for the process at 25 °C.

The following reaction is exothermic. 2N₂O(g) → 2N₂(g) + O₂(g) This means the reaction:

For the reaction, 2 O₃(g) → 3 O₂(g) S° (J/mol K) 238.8 205.0 What is ΔS°rxn?