Question 1

For a chemical reaction to be spontaneous at all 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) It is not possible for a reaction to be spontaneous at all temperatures. 
A) Δ S° > 0, Δ H° > 0 
B) Δ S° > 0, Δ H°  0 
E) It is not possible for a reaction to be spontaneous at all temperatures. B

Question 2

The term microstate refers to the energy state of a single molecule in a system of many molecules.

Accepted Answer

A) True 
 B)False  False

Question 3

"A diamond is forever" is one of the most successful advertising slogans of all time. But is it true? For the reaction shown below, calculate the standard free energy change at 298K and determine whether or not a diamond is "forever". C(diamond) → C(graphite)
Data: ΔHf°(diamond) = 1.895 kJ/mol; S°(diamond) = 2.337 J mol−1K−1; S°(graphite) = 5.740 J mol−1K−1.

Accepted Answer

A) Δ G° = 2.19 kJ; forever 
B) Δ G° = −1.90 kJ; not forever 
C) Δ G° = −2.90 kJ; not forever 
D) Δ G° = 1.90 kJ; forever 
E) Δ G° = < −1000 kJ; not forever 
A) Δ G° = 2.19 kJ; forever 
B) Δ G° = −1.90 kJ; not forever 
C) Δ G° = −2.90 kJ; not forever 
D) Δ G° = 1.90 kJ; forever 
E) Δ G° = < −1000 kJ; not forever C

Question 4

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) Sublimation 
A) Melting 
B) Heating a gas 
C) Vaporization 
D) Condensation 
E) Sublimation

Question 5

A reaction has ΔG = 10.0 kJ and ΔG° = 15.0 kJ at a temperature of 50°C. Calculate the value of the reaction quotient   under these conditions.

Accepted Answer

A) 0.16 
B) 9.1 × 10 −5 
C) 1.1 × 10 4 
D) 6.4 
E) 6.0 × 10 −6 
A) 0.16 
B) 9.1 × 10 −5 
C) 1.1 × 10 4 
D) 6.4 
E) 6.0 × 10 −6

Question 6

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 kJ 
A) −69881 kJ 
B) 48.4 kJ 
C) 99.1 kJ 
D) 240 kJ 
E) 441 kJ

Question 7

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)

Accepted Answer

A) 8.2 × 10 19 
B) 0.96 
C) 0.58 
D) 1.2 × 10 −20 
E) 1.4 × 10 −46 
A) 8.2 × 10 19 
B) 0.96 
C) 0.58 
D) 1.2 × 10 −20 
E) 1.4 × 10 −46

Question 8

Which of the following should have the greatest molar entropy at 298 K?

Accepted Answer

A) CH 4( g) 
B) H 2O( l) 
C) NaCl( s) 
D) N 2O 4( g) 
E) H 2( g) 
A) CH 4( g) 
B) H 2O( l) 
C) NaCl( s) 
D) N 2O 4( g) 
E) H 2( g)

Question 9

Given: H2O(l) → H2O(s) ΔH° = −6.02 kJ at 273K Calculate the entropy change of the surroundings (ΔSsurr) when one mole of water freezes at 0°C and a pressure of one atmosphere.

Accepted Answer

A) 22.1 J/K 
B) −22.1 J/K 
C) 397 J/K 
D) −397 J/K 
E) 0.022 J/K 
A) 22.1 J/K 
B) −22.1 J/K 
C) 397 J/K 
D) −397 J/K 
E) 0.022 J/K

Question 10

What is the free energy change, ΔG°, for the equilibrium between hydrogen iodide, hydrogen, and iodine at 453°C? Kc = 0.020 2HI(g) ⇄ H2(g) + I2(g)

Accepted Answer

A) 6.4 kJ 
B) 8.8 kJ 
C) 15 kJ 
D) 19 kJ 
E) 24 kJ 
A) 6.4 kJ 
B) 8.8 kJ 
C) 15 kJ 
D) 19 kJ 
E) 24 kJ

Question 11

You are given pure samples of ammonia, NH3(g), and nitrogen trifluoride, NF3(g). What prediction would you make concerning their standard molar entropies at 298 K?

Accepted Answer

A) S° ammonia > S° nitrogen trifluoride 
B) S° ammonia nitrogen trifluoride 
C) S° ammonia ≈ S° nitrogen trifluoride 
D) Other conditions need to be specified before a reliable prediction can be made. 
E) Even if more conditions are specified, a reliable prediction cannot be made. 
A) S° ammonia > S° nitrogen trifluoride 
B) S° ammonia nitrogen trifluoride 
C) S° ammonia ≈ S° nitrogen trifluoride 
D) Other conditions need to be specified before a reliable prediction can be made. 
E) Even if more conditions are specified, a reliable prediction cannot be made.

Question 12

As a chemical reaction proceeds toward equilibrium, the free energy of the system decreases.

Accepted Answer

A) True 
 B)False

Question 13

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.

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. 
A) −293.4 kJ 
B) 293.4 kJ 
C) −102.8 kJ 
D) 102.8 kJ 
E) None of these choices are correct.

Question 14

A sample of water is heated at a constant pressure of one atmosphere. Initially, the sample is ice at 260 K, and at the end the sample consists of steam at 400 K. In which of the following 5K temperature intervals would there be the greatest increase in the entropy of the sample?

Accepted Answer

A) From 260 K to 265 K 
B) From 275 K to 280 K 
C) From 360 K to 365 K 
D) 370 K to 375 K 
E) From 395 K to 400 K 
A) From 260 K to 265 K 
B) From 275 K to 280 K 
C) From 360 K to 365 K 
D) 370 K to 375 K 
E) From 395 K to 400 K

Question 15

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. 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 16

Sulfuryl dichloride is formed when sulfur dioxide reacts with chlorine. The data refer to 298 K. SO2(g) + Cl2(g) → SO2Cl2(g)
  What is the value of ΔG° for this reaction at 600 K?

Accepted Answer

A) −162.8 kJ 
B) −40.1 kJ 
C) −28.4 kJ 
D) 28.4 kJ 
E) 162.8 kJ 
A) −162.8 kJ 
B) −40.1 kJ 
C) −28.4 kJ 
D) 28.4 kJ 
E) 162.8 kJ

Question 17

Consider the following quantities used in thermodynamics: E, H, q, w, S, G. How many of them are state functions?

Accepted Answer

A) 0 
B) 1 
C) 2 
D) 3 
E) 4 
A) 0 
B) 1 
C) 2 
D) 3 
E) 4

Question 18

In which one of these pairs will the entropy of the first substance be greater than that of the second? Assume P and T are the same for each pair, unless stated otherwise.

Accepted Answer

A) 1 mole of F 2( g); 1 mole of Cl 2( g) 
B) 1 mole of I 2( s); 1 mole of I 2( g) 
C) 1 mole of CaCO 3( s); 1 mole of CaO( s)plus 1 mole of CO 2( g) 
D) 1 mole of H 2( g)at 25°C; 1 mole of H 2( g)at 50°C 
E) 1 mole of O 3( g); 1 mole of O 2( g) 
A) 1 mole of F 2( g); 1 mole of Cl 2( g) 
B) 1 mole of I 2( s); 1 mole of I 2( g) 
C) 1 mole of CaCO 3( s); 1 mole of CaO( s)plus 1 mole of CO 2( g) 
D) 1 mole of H 2( g)at 25°C; 1 mole of H 2( g)at 50°C 
E) 1 mole of O 3( g); 1 mole of O 2( g)

Question 19

Which of the following is true for pure oxygen gas, O2(g) at 25°C?

Accepted Answer

A) Δ H° f > 0 
B) Δ H° f f > 0 
D) Δ G° f  0 
A) Δ H° f > 0 
B) Δ H° f f > 0 
D) Δ G° f  0

Question 20

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

Accepted Answer

A) Δ H° f = 0 for Al( s)at 298 K 
B) Δ G° f = 0 for H 2( g)at 298 K 
C) S° = 51.446 J/(mol·K)for Na( s)at 298 K 
D) q sys 2O( l)→ H 2O(s)at 0°C 
E) None of these choices are correct. 
A) Δ H° f = 0 for Al( s)at 298 K 
B) Δ G° f = 0 for H 2( g)at 298 K 
C) S° = 51.446 J/(mol·K)for Na( s)at 298 K 
D) q sys 2O( l)→ H 2O(s)at 0°C 
E) None of these choices are correct.

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

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

The term microstate refers to the energy state of a single molecule in a system of many molecules.

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

A reaction has ΔG = 10.0 kJ and ΔG° = 15.0 kJ at a temperature of 50°C. Calculate the value of the reaction quotient under these conditions.

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?

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)

Which of the following should have the greatest molar entropy at 298 K?

Given: H2O(l) → H2O(s) ΔH° = −6.02 kJ at 273K Calculate the entropy change of the surroundings (ΔSsurr) when one mole of water freezes at 0°C and a pressure of one atmosphere.

What is the free energy change, ΔG°, for the equilibrium between hydrogen iodide, hydrogen, and iodine at 453°C? Kc = 0.020 2HI(g) ⇄ H2(g) + I2(g)

You are given pure samples of ammonia, NH3(g), and nitrogen trifluoride, NF3(g). What prediction would you make concerning their standard molar entropies at 298 K?

As a chemical reaction proceeds toward equilibrium, the free energy of the system decreases.

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.

A sample of water is heated at a constant pressure of one atmosphere. Initially, the sample is ice at 260 K, and at the end the sample consists of steam at 400 K. In which of the following 5K temperature intervals would there be the greatest increase in the entropy of the sample?

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

Sulfuryl dichloride is formed when sulfur dioxide reacts with chlorine. The data refer to 298 K. SO2(g) + Cl2(g) → SO2Cl2(g) What is the value of ΔG° for this reaction at 600 K?

Consider the following quantities used in thermodynamics: E, H, q, w, S, G. How many of them are state functions?

In which one of these pairs will the entropy of the first substance be greater than that of the second? Assume P and T are the same for each pair, unless stated otherwise.

Which of the following is true for pure oxygen gas, O2(g) at 25°C?

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

Keys to the Study of Chemistry: Definitions, Units, and Problem Solving

The Components of Matter

Stoichiometry of Formulas and Equations

Three Major Classes of Chemical Reactions

Gases and the Kinetic-Molecular Theory

Thermochemistry: Energy Flow and Chemical Change

Quantum Theory and Atomic Structure

Electron Configuration and Chemical Periodicity

Models of Chemical Bonding

The Shapes of Molecules

Theories of Covalent Bonding

Intermolecular Forces: Liquids, Solids, and Phase Changes

The Properties of Mixtures: Solutions and Colloids

Periodic Patterns in the Main-Group Elements

Organic Compounds and the Atomic Properties of Carbon

Kinetics: Rates and Mechanisms of Chemical Reactions

Equilibrium: the Extent of Chemical Reactions

Acid-Base Equilibria

Ionic Equilibria in Aqueous Systems

Electrochemistry: Chemical Change and Electrical Work

The Elements in Nature and Industry

Transition Elements and Their Coordination Compounds

Nuclear Reactions and Their Applications

Filters

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?

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)

Given: H₂O(l) → H₂O(s) ΔH° = −6.02 kJ at 273K Calculate the entropy change of the surroundings (ΔS_surr) when one mole of water freezes at 0°C and a pressure of one atmosphere.

What is the free energy change, ΔG°, for the equilibrium between hydrogen iodide, hydrogen, and iodine at 453°C? K_c = 0.020 2HI(g) ⇄ H₂(g) + I₂(g)

You are given pure samples of ammonia, NH₃(g), and nitrogen trifluoride, NF₃(g). What prediction would you make concerning their standard molar entropies at 298 K?

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.

Sulfuryl dichloride is formed when sulfur dioxide reacts with chlorine. The data refer to 298 K. SO₂(g) + Cl₂(g) → SO₂Cl₂(g) What is the value of ΔG° for this reaction at 600 K?

Which of the following is true for pure oxygen gas, O₂(g) at 25°C?