Question 1

Which of the following statements best explains why diamonds, though thermodynamically unstable at room temperature and pressure, persist for millions of years?

Accepted Answer

Diamonds are kinetically stable under ambient conditions, so the rate of conversion to graphite is extremely slow.

Question 2

A solid sublimes to a gas at constant temperature and pressure. What is the sign of the entropy change ($$\Delta S) $$for this process, and why?

Accepted Answer

Positive; the gas phase has more microstates and greater dispersal of matter than the solid.

Question 3

Which of the following best describes the second law of thermodynamics?

Accepted Answer

All spontaneous changes cause an increase in the entropy of the universe ($$\Delta S_{univ} \u003e 0).$$

Question 4

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

Accepted Answer

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

Question 5

Which equation correctly relates the standard free energy change ($$\Delta G^\circ) to $$the standard enthalpy and entropy changes?

Accepted Answer

$$\Delta G^\circ = \Delta H^\circ - T\Delta S^\circ$$

Question 6

Consider the process: $$\mathrm{H_2O(s) \rightarrow H_2O(l)} at$$ $$-10^\circC. $$Given $$\Delta S_{sys} = 22.1\ \mathrm{J/K}$$ and $$q_{surr} = -6.00\ \mathrm{kJ}$$, what is the sign of $$\Delta S_{univ}$$ and is the process spontaneous?

Accepted Answer

$$\Delta S_{univ} \u003c 0$$; the process is nonspontaneous.

Question 7

Which of the following processes results in a decrease in entropy ($$\Delta S \u003c 0$$)?

Accepted Answer

Condensation of a gas to a liquid.

Question 8

The entropy of a pure, perfectly crystalline substance at absolute zero (0 K) is:

Accepted Answer

Zero, according to the third law of thermodynamics.

Question 9

Which of the following best describes the relationship between microstates and entropy?

Accepted Answer

Entropy increases as the number of possible microstates increases.

Question 10

A reaction has $$\Delta H \u003c 0$$ and $$\Delta S \u003c 0. $$When will this reaction be spontaneous?

Accepted Answer

At low temperatures, where $$|\Delta H| \u003e |T\Delta S|.$$

Question 11

Which of the following is a correct statement about the spontaneity of a process?

Accepted Answer

A process is spontaneous if $$\Delta G \u003c 0$$ under the given conditions.

Question 12

Which of the following best explains why the dissolution of a salt in water is usually accompanied by an increase in entropy?

Accepted Answer

The ions experience greater freedom of motion and more possible interactions in solution.

Question 13

Given the following standard entropies: $$S^\circ(\mathrm{CO_2$(g)}) = 213.8\ \mathrm{J/(mol\cdot K)}$$, $$S^\circ(\mathrm{CH_3OH(l)}) = 126.8\ \mathrm{J/(mol\cdot K)}$$, $$S^\circ(\mathrm{O_2$(g)}) = 205.03\ \mathrm{J/(mol\cdot K)}$$, calculate $$\Delta S^\circ$$ for the reaction: $$2\mathrm{CH_3OH(l)} + 3\mathrm{O_2$(g)} \rightarrow 2\mathrm{CO_2$(g)} + 4\mathrm{H_2O(l)} ($$Assume $$S^\circ(\mathrm{H_2O(l)}) = 70.0\ \mathrm{J/(mol\cdot K)}).$$

Accepted Answer

$$\Delta S^\circ = -161.1\ \mathrm{J/K}$$

Question 14

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

Accepted Answer

$$\Delta G = 0$$ and $$\Delta S_{univ} = 0$$

Question 15

Which of the following best describes the effect of temperature on the spontaneity of a process with $$\Delta H \u003e 0$$ and $$\Delta S \u003c 0$$?

Accepted Answer

The process is nonspontaneous at all temperatures.

Question 16

Which of the following equations correctly relates the standard free energy change to the equilibrium constant $$K at $$temperature $$T$$?

Accepted Answer

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

Question 17

A reaction has $$\Delta G^\circ = 58.43\ \mathrm{kJ/mol} at 25$^\circC. $$What does this indicate about the reaction under standard conditions?

Accepted Answer

The reaction is nonspontaneous under standard conditions.

Question 18

Which of the following best describes the relationship between $$\Delta G$$ and the direction of a chemical reaction?

Accepted Answer

If $$\Delta G \u003c 0$$, the reaction proceeds spontaneously in the forward direction.

Question 19

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

Accepted Answer

A mixture of two different gases has higher entropy than a pure gas at the same conditions.

Thermodynamics: Spontaneity, Entropy, and Free Energy

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