Q: According to the Second Law of Thermodynamics, which of the following must be true for a process to be spontaneous?

$$\Delta S_{\text{univ}} \u003e 0$$

Q: Given the reaction: $$2 \text{NO}(g) + \text{O}_2(g) \rightarrow 2 \text{NO}_2(g)$$, which equation would you use to calculate the standard entropy change?

$$\Delta S^\circ_{\text{rxn}} = \sum n_p S^\circ(\text{products}) - \sum n_r S^\circ(\text{reactants})$$

Question 1

Which of the following best describes the difference between the domain of thermodynamics and the domain of kinetics in a chemical reaction, as illustrated in the energy diagram?

Accepted Answer

Thermodynamics concerns the initial and final states (reactants and products), while kinetics concerns the pathway and energy barrier between them.

Question 2

According to the Second Law of Thermodynamics, which of the following must be true for a process to be spontaneous?

Accepted Answer

$$\Delta S_{	ext{univ}} \u003e 0$$

Question 3

Which of the following processes would you expect to have a decrease in entropy?

Accepted Answer

2 NO$$_2 (g$$) $$\rightarrow N$_2O$_4 (g)$$

Question 4

Given the reaction: $$2 	ext{NO}(g) + 	ext{O}_2(g) ightarrow 2 	ext{NO}_2(g)$$, which equation would you use to calculate the standard entropy change?

Accepted Answer

$$\Delta S^\circ_{	ext{rxn}} = \sum n_p S^\circ(	ext{products}) - \sum n_r S^\circ(	ext{reactants})$$

Question 5

A reaction has $$\Delta H  0. $$According to Table 17.5, what can you conclude about its spontaneity?

Accepted Answer

It is spontaneous at all temperatures.

Question 6

Which of the following statements about $$\Delta G$$ and spontaneity is correct?

Accepted Answer

A process is spontaneous if $$\Delta G \u003c 0.$$

Question 7

For the reaction $$	ext{C} (s) + 	ext{H}_2	ext{O} (g) ightarrow 	ext{CO} (g) + 	ext{H}_2 (g)$$, $$\Delta S^\circ_{	ext{sys}} = 133.6 J/$$mol·K and $$\Delta H^\circ_{	ext{sys}} = 131.3 kJ/$$mol. At what minimum temperature (in K) does this reaction become spontaneous?

Accepted Answer

983

Question 8

Which equation correctly relates the standard free energy change to the equilibrium constant?

Accepted Answer

$$\Delta G^\circ = -RT \ln K$$

Question 9

A chemical reaction has an equilibrium constant $$K \u003c 1. $$What is true about $$\Delta G^\circ$$ for this reaction?

Accepted Answer

$$\Delta G^\circ \u003e 0$$

Question 10

Which of the following best describes the effect of increasing pressure on the free energy of a gas?

Accepted Answer

Increasing pressure increases the free energy of a gas.

Question 11

Which of the following is the correct expression for the free energy change under non-standard conditions?

Accepted Answer

$$\Delta G = \Delta G^\circ + RT \ln Q$$

Question 12

A reaction is spontaneous under a certain set of conditions. What can you conclude about $$\Delta G$$ and $$Q$$ for this reaction under these conditions?

Accepted Answer

$$\Delta G \u003c 0$$ and $$Q \u003c K$$

Question 13

Which of the following scenarios will always result in a nonspontaneous process at any temperature?

Accepted Answer

$$\Delta S  0$$

Question 14

Which of the following best explains why the melting of ice at room temperature is a spontaneous process?

Accepted Answer

The process increases the entropy of the system.

Question 15

Which of the following is the correct relationship for the entropy change of the universe?

Accepted Answer

$$\Delta S_{	ext{univ}} = \Delta S_{	ext{sys}} + \Delta S_{	ext{surr}}$$

Question 16

Which of the following is true about the maximum work ($$w_{	ext{max}}) $$that can be obtained from a chemical reaction?

Accepted Answer

$$w_{	ext{max}} = \Delta G$$

Question 17

Which of the following best describes the effect of temperature on the spontaneity of a reaction with $$\Delta H \u003e 0$$ and $$\Delta S \u003e 0$$?

Accepted Answer

The reaction is spontaneous only at high temperatures.

Chapter 19: Spontaneity, Entropy, and Free Energy – Thermodynamics Study Guide

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