Question 1

Which of the following best describes the Second Law of Thermodynamics?

Accepted Answer

The total entropy of the universe increases in a spontaneous process.

Question 2

A power plant operates by converting heat from burning fuel into work. Why can't the efficiency of this process be 100%?

Accepted Answer

Some heat must always be transferred to the cold surroundings, as required by the Second Law of Thermodynamics.

Question 3

Which of the following processes is spontaneous under standard conditions?

Accepted Answer

A cube of sugar dissolving in a cup of hot tea.

Question 4

According to the Third Law of Thermodynamics, what is the entropy of a perfectly crystalline substance at 0 K?

Accepted Answer

$$S = 0$$

Question 5

For the reaction $$A(g) + 2B(g) \rightarrow AB_2$(g)$$, what is the sign of $$\Delta S$$?

Accepted Answer

Negative, because the number of gas molecules decreases.

Question 6

Which of the following statements about entropy ($$S) is $$correct?

Accepted Answer

Entropy is a measure of the dispersal of energy in a system.

Question 7

Given the equation $$\Delta G = \Delta H - T\Delta S$$, which condition will always result in a spontaneous process?

Accepted Answer

$$\Delta G \u003c 0$$

Question 8

A refrigerator removes heat $$q$$ from its interior at temperature $$T_{in}$$ and releases heat $$q' to $$the room at temperature $$T_{out}. $$Which statement is true?

Accepted Answer

The heat released to the room ($$q') is $$greater than the heat removed from the interior ($$q).$$

Question 9

Which of the following pairs has the greater entropy?

Accepted Answer

2.0 mol of CO$$_2$$ gas at 20$$^\circC $$and 1 atm

Question 10

For a reversible process at equilibrium, the entropy change is given by:

Accepted Answer

$$\Delta S = \frac{q_{rev}}{T}$$

Question 11

Consider the decomposition of dinitrogen tetroxide: $$N_2O_4(g) \rightarrow 2NO_2(g). $$Which of the following is true as temperature increases?

Accepted Answer

The reaction becomes more spontaneous at higher temperatures.

Question 12

At equilibrium, what is the value of $$\Delta G$$ for a chemical reaction?

Accepted Answer

$$\Delta G = 0$$

Question 13

Which of the following statements about spontaneous reactions is correct?

Accepted Answer

A spontaneous reaction can be endothermic or exothermic.

Question 14

If a process occurs such that $$\Delta S_{universe} \u003e 0$$, what can be said about $$\Delta G$$ for the system?

Accepted Answer

$$\Delta G \u003c 0$$

Question 15

Which of the following best explains why the entropy of a substance increases as it changes from solid to liquid to gas?

Accepted Answer

The number of possible ways to distribute energy increases.

Question 16

For the reaction $$A(g) + 2B(g) \rightarrow AB_2$(g)$$, what is the value of $$\Delta G$$ before equilibrium is reached?

Accepted Answer

Negative, because the reaction is proceeding spontaneously toward equilibrium.

Question 17

Which of the following is a correct statement about the relationship between $$\Delta H$$, $$\Delta S$$, and $$\Delta G at $$equilibrium?

Accepted Answer

$$\Delta H = T\Delta S$$

Question 18

Which of the following is NOT a correct statement about entropy?

Accepted Answer

The entropy of a system always increases in a spontaneous process.

Question 19

A chemical reaction has $$\Delta H \u003e 0$$ and $$\Delta S \u003e 0. $$Under what conditions will the reaction be spontaneous?

Accepted Answer

At high temperatures, where $$T\Delta S \u003e \Delta H$$

Question 20

Which of the following best describes the entropy change when a solid is melted to a liquid at its melting point?

Accepted Answer

$$\Delta S = \frac{q_{fus}}{T_{fus}}$$

Thermodynamics: Entropy, Spontaneity, and the Laws of Thermodynamics

Study Guide - Practice Questions

Study Guide - Flashcards