Question 1

The temperature at which the following process reaches equilibrium at 1.0 atm is the normal melting point for phosphoric acid. H3PO4(s)⇄ H3PO4(l)
Use the following thermodynamic information at 298 K to determine this temperature.

Accepted Answer

A) 286 K 
B) 305 K 
C) 315 K 
D) 347 K 
E) 3170 K

Question 2

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

Accepted Answer

A) Δ H° > 0, Δ S° > 0 B) Δ H° > 0, Δ S° 0 D) Δ H° < 0, Δ S° < 0 E) None of these choices are correct.

Question 3

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

Accepted Answer

A) H 2O( l)→ H 2O( s)at 25°C 
B) CO 2( s)→ CO 2( g)at 0°C 
C) 2H 2O( g)→ 2H 2(g)+ O 2( g) 
D) C(graphite)→ C(diamond)at 25°C and 1 atm pressure 
E) None of these choices are correct.

Question 4

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

Accepted Answer

A) Δ S° > 0, Δ H° > 0 
B) Δ S° > 0, Δ H°  0 
E) Δ G° > 0

Question 5

The formation constant for the reaction Ag+(aq) + 2NH3(aq) ⇄ Ag(NH3)2+(aq)
Is Kf = 1.7 × 107 at 25°C. What is ΔG° at this temperature?

Accepted Answer

A) −1.5 kJ 
B) −3.5 kJ 
C) −18 kJ 
D) −23 kJ 
E) −41 kJ

Question 6

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

Accepted Answer

A) Δ S° sys = Δ S° surr 
B) Δ S° sys = −Δ S° surr 
C) Δ S° sys = Δ S° surr = 0 
D) Δ S° univ > 0 
E) None of these choices are correct.

Question 7

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

Accepted Answer

A) Δ H sys sys > 0 
C) Δ S surr univ > 0 
E) Δ G sys = 0

Question 8

Which relationship or statement best describes ΔS° for the following reaction? C2H5OH(l) + 3O2(g) → 2CO2(g) + 3H2O(l)

Accepted Answer

A) Δ S° ≈ 0 
B) Δ S°  0 
D) Δ S° = Δ H°/ T 
E) More information is needed to make a reasonable prediction.

Question 9

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

Accepted Answer

A) Δ H > 0 
B) Δ H sys > 0 
D) Δ S surr > Δ S sys 
E) Δ S > Δ H/ T

Question 10

Calculate ΔS° for the reaction 4Cr(s) + 3O2(g) → 2Cr2O3(s)

Accepted Answer

A) −548.1 J/K 
B) −147.7 J/K 
C) 147.7 J/K 
D) 310.1 J/K 
E) 548.1 J/K

Question 11

Calculate ΔS° for the combustion of propane. C3H8(g) + 5O2(g) → 3CO2(g) + 4H2O(g)

Accepted Answer

A) −100.9 J/K 
B) −72.5 J/K 
C) 72.5 J/K 
D) 100.9 J/K 
E) 877.5 J/K

Question 12

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.

Question 13

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

Accepted Answer

A) Δ S° ≈ 0 
B) Δ S°  0 
D) Δ S° = Δ H°/ T 
E) More information is needed to make a reasonable prediction.

Question 14

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

Accepted Answer

A) O 2( g), 300 K → O 2( g), 400 K 
B) H 2O( s), 0°C → H 2O( l), 0°C 
C) N 2( g), 25°C → N 2( aq), 25°C 
D) NH 3( l), −34.5°C → NH 3( g), −34.5°C 
E) 2H 2O 2( g)→ 2H 2O( g)+ O 2( g)

Question 15

The second law of thermodynamics tells us that

Accepted Answer

A) the entropy of the universe is constant. 
B) entropy is neither created nor destroyed. 
C) the universe proceeds toward a state of lower entropy. 
D) the universe proceeds toward a state of higher entropy. 
E) the universe cannot create entropy.

Question 16

Calculate ΔS° for the reaction SiCl4(g) + 2Mg(s) → 2MgCl2(s) + Si(s)

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/K

Question 17

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?

Accepted Answer

A) Δ H° > 0 
B) Δ S° > 0 
C) The reaction is spontaneous at high temperatures. 
D) Δ S° increases with temperature while Δ H° remains constant. 
E) There exists a certain temperature at which Δ H° = TΔ S°.

Question 18

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.

Question 19

Calculate ΔG° for the combustion of propane. C3H8(g) + 5O2(g) → 3CO2(g) + 4H2O(g)

Accepted Answer

A) −2073.1 kJ 
B) −1387.3 kJ 
C) −598.5 kJ 
D) 598.5 kJ 
E) 2073.1 kJ

Question 20

Which relationship or statement best describes ΔS° for the following reaction? 2NH3(g) + 2ClF3(g) → 6HF(g) + N2(g) + Cl2(g)

Accepted Answer

A) Δ S° ≈ 0 
B) Δ S°  0 
D) Δ S° = Δ H°/ T 
E) More information is needed to make a reasonable prediction.

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

The temperature at which the following process reaches equilibrium at 1.0 atm is the normal melting point for phosphoric acid. H₃PO₄(s) ⇄ H₃PO₄(l) Use the following thermodynamic information at 298 K to determine this temperature.

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

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

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

The formation constant for the reaction Ag⁺(aq) + 2NH₃(aq) ⇄ Ag(NH₃) ₂⁺(aq) Is K_f = 1.7 × 10⁷ at 25°C. What is ΔG° at this temperature?

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

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

Which relationship or statement best describes ΔS° for the following reaction? C₂H₅OH(l) + 3O₂(g) → 2CO₂(g) + 3H₂O(l)

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

Calculate ΔS° for the reaction 4Cr(s) + 3O₂(g) → 2Cr₂O₃(s)

Calculate ΔS° for the combustion of propane. C₃H₈(g) + 5O₂(g) → 3CO₂(g) + 4H₂O(g)

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?

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

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

The second law of thermodynamics tells us that

Calculate ΔS° for the reaction SiCl₄(g) + 2Mg(s) → 2MgCl₂(s) + Si(s)

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?

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?

Calculate ΔG° for the combustion of propane. C₃H₈(g) + 5O₂(g) → 3CO₂(g) + 4H₂O(g)

Which relationship or statement best describes ΔS° for the following reaction? 2NH₃(g) + 2ClF₃(g) → 6HF(g) + N₂(g) + Cl₂(g)

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

The temperature at which the following process reaches equilibrium at 1.0 atm is the normal melting point for phosphoric acid. H3PO4(s) ⇄ H3PO4(l) Use the following thermodynamic information at 298 K to determine this temperature.

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

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

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

The formation constant for the reaction Ag+(aq) + 2NH3(aq) ⇄ Ag(NH3) 2+(aq) Is Kf = 1.7 × 107 at 25°C. What is ΔG° at this temperature?

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

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

Which relationship or statement best describes ΔS° for the following reaction? C2H5OH(l) + 3O2(g) → 2CO2(g) + 3H2O(l)

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

Calculate ΔS° for the reaction 4Cr(s) + 3O2(g) → 2Cr2O3(s)

Calculate ΔS° for the combustion of propane. C3H8(g) + 5O2(g) → 3CO2(g) + 4H2O(g)

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?

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

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

The second law of thermodynamics tells us that

Calculate ΔS° for the reaction SiCl4(g) + 2Mg(s) → 2MgCl2(s) + Si(s)

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?

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?

Calculate ΔG° for the combustion of propane. C3H8(g) + 5O2(g) → 3CO2(g) + 4H2O(g)

Which relationship or statement best describes ΔS° for the following reaction? 2NH3(g) + 2ClF3(g) → 6HF(g) + N2(g) + Cl2(g)

The temperature at which the following process reaches equilibrium at 1.0 atm is the normal melting point for phosphoric acid. H₃PO₄(s) ⇄ H₃PO₄(l) Use the following thermodynamic information at 298 K to determine this temperature.

The formation constant for the reaction Ag⁺(aq) + 2NH₃(aq) ⇄ Ag(NH₃) ₂⁺(aq) Is K_f = 1.7 × 10⁷ at 25°C. What is ΔG° at this temperature?

Which relationship or statement best describes ΔS° for the following reaction? C₂H₅OH(l) + 3O₂(g) → 2CO₂(g) + 3H₂O(l)

Calculate ΔS° for the reaction 4Cr(s) + 3O₂(g) → 2Cr₂O₃(s)

Calculate ΔS° for the combustion of propane. C₃H₈(g) + 5O₂(g) → 3CO₂(g) + 4H₂O(g)

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

Calculate ΔS° for the reaction SiCl₄(g) + 2Mg(s) → 2MgCl₂(s) + Si(s)

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?

Calculate ΔG° for the combustion of propane. C₃H₈(g) + 5O₂(g) → 3CO₂(g) + 4H₂O(g)

Which relationship or statement best describes ΔS° for the following reaction? 2NH₃(g) + 2ClF₃(g) → 6HF(g) + N₂(g) + Cl₂(g)