Question 1

Which of the following processes results in an increase in entropy ($$\Delta S \u003e 0$$)?

Accepted Answer

Mixing two different ideal gases at constant temperature and pressure

Question 2

According to Boltzmann’s equation, the entropy $$S of a $$system is given by:

Accepted Answer

$$S = k_B \ln W$$

Question 3

A sample of gas expands isothermally and reversibly from volume $$V_i to$$ $$V_f. $$What is the entropy change of the gas?

Accepted Answer

$$\Delta S = nR \ln \left( \frac{V_f}{V_i} \right)$$

Question 4

Which statement best describes the Second Law of Thermodynamics?

Accepted Answer

All spontaneous processes increase the entropy of the universe.

Question 5

For the vaporization of water at its normal boiling point, which equation correctly gives the standard entropy change?

Accepted Answer

$$\$$Delta_{vap}$$S^\circ = \frac{\$$Delta_{vap}$$H^\circ}{T_{bp}}$$

Question 6

Which of the following will always result in a spontaneous process at all temperatures?

Accepted Answer

$$\Delta H  0$$

Question 7

The standard Gibbs free energy change for a reaction is related to the equilibrium constant $$K by $$which equation?

Accepted Answer

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

Question 8

Which of the following statements about the entropy of a substance is correct?

Accepted Answer

The entropy of a perfect crystal at 0 K is zero.

Question 9

A chemical reaction has $$\Delta H = +50 kJ $$and $$\Delta S = +120 J/K. At $$what temperature will the reaction become spontaneous?

Accepted Answer

At temperatures above $$417 K$$

Question 10

Which process below is best described as an increase in the number of microstates ($$W) $$available to a system?

Accepted Answer

Allowing a gas to expand into a vacuum

Question 11

Given the reaction $$2NO(g) + O_2$(g) \rightarrow 2NO_2(g)$$, and the following standard molar entropies: $$S^\circ(NO) = 210.8 J/$$mol·K, $$S^\circ(O_2$) = 205.1 J/$$mol·K, $$S^\circ(NO_2$) = 240.1 J/$$mol·K, calculate $$\Delta_r S^\circ.$$

Accepted Answer

$$-146.5 J/$$mol·K

Question 12

Which of the following correctly expresses the entropy change for heating a substance from $$T_i to$$ $$T_f at $$constant pressure?

Accepted Answer

$$\Delta S = C_p \ln \left( \frac{T_f}{T_i} \right)$$

Question 13

If $$\Delta_r G \u003c 0$$ for a chemical reaction, what does this indicate about the reaction?

Accepted Answer

The reaction is spontaneous in the forward direction.

Question 14

Which of the following is true for the mixing of two ideal gases at constant temperature and pressure?

Accepted Answer

The entropy of the system increases.

Question 15

Which of the following is the correct expression for the entropy change of the surroundings for a process at constant temperature?

Accepted Answer

$$\Delta S_{surr} = -\frac{q_{sys}}{T_{surr}}$$

Question 16

Which of the following statements about the relationship between $$\Delta G$$ and $$K is $$correct?

Accepted Answer

If $$\Delta G^\circ = 0$$, then $$K = 1$$

Question 17

Which of the following best describes Trouton's Rule?

Accepted Answer

The entropy of vaporization for many liquids at their normal boiling points is approximately $$87 J/$$mol·K.

Question 18

Which of the following is the correct van’t Hoff equation relating the equilibrium constant $$K to $$temperature?

Accepted Answer

$$\ln K = -\frac{\Delta H^\circ}{RT} + \frac{\Delta S^\circ}{R}$$

Question 19

Which of the following is a correct statement about the effect of molecular complexity on standard molar entropy ($$S^\circ$$)?

Accepted Answer

Standard molar entropy increases as the number of atoms per molecule increases.

Entropy, Spontaneity, and Gibbs Free Energy: A Study Guide

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