Q: Calculate the standard entropy change ($$\Delta S^\circ) $$for the reaction: 4Fe(s) + 3O$$_2(g$$) → 2Fe$$_2O$_3(s$$), given $$S^\circ$$[Fe(s)] = 27.23 J mol$$^{-1} K$^{-1}$$, $$S^\circ$$[O$$_2(g$$)] = 205 J mol$$^{-1} K$^{-1}$$, $$S^\circ$$[Fe$$_2O$_3(s$$)] = 87.4 J mol$$^{-1} K$^{-1}.$$

$$\Delta S^\circ = 2 \times 87.4 - [4 \times 27.23 + 3 \times 205] = -549.5 J $$mol$$^{-1} K$^{-1}$$

Q: For the reaction: 2SO$$_2(g) + O$_2(g$$) → 2SO$$_3(g$$), given $$\Delta G_f^\circ(SO$_2) = -300.4 kJ/$$mol and $$\Delta G_f^\circ(SO$_3) = -370.4 kJ/$$mol, what is $$\Delta G^\circ$$ for the reaction?

$$\Delta G^\circ = 2 \times (-370.4) - [2 \times (-300.4) + (-1) \times 0] = -139.2 kJ$$

Question 1

Which of the following statements best describes the difference between thermodynamics and kinetics in chemical reactions?

Accepted Answer

Thermodynamics tells us whether a reaction can occur, while kinetics tells us how fast it occurs.

Question 2

Which equation correctly expresses the First Law of Thermodynamics for a closed system?

Accepted Answer

$$E = q + w$$

Question 3

A gas expands spontaneously into a vacuum. Which of the following is true about this process?

Accepted Answer

The process is spontaneous and irreversible.

Question 4

Which of the following best describes entropy ($$S$$)?

Accepted Answer

A measure of the disorder or randomness of a system.

Question 5

Which process results in an increase in the entropy of the system?

Accepted Answer

N$$_2O$_4(g$$) → 2NO$$_2(g)$$

Question 6

Which of the following is true for a spontaneous process at constant temperature and pressure?

Accepted Answer

$$\Delta G \u003c 0$$

Question 7

The dissolution of ammonium nitrate in water is endothermic ($$\Delta H \u003e 0) $$but spontaneous. What does this indicate about the entropy change ($$\Delta S) $$for the process?

Accepted Answer

$$\Delta S$$ must be positive and large enough to outweigh $$\Delta H.$$

Question 8

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

Accepted Answer

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

Question 9

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

Accepted Answer

$$\Delta S_{universe} \u003e 0$$

Question 10

Which of the following statements about the Third Law of Thermodynamics is correct?

Accepted Answer

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

Question 11

Which of the following will have the highest standard molar entropy ($$S^\circ$$)?

Accepted Answer

1 mole N$$_2(g)$$

Question 12

Calculate the standard entropy change ($$\Delta S^\circ) $$for the reaction: 4Fe(s) + 3O$$_2(g$$) → 2Fe$$_2O$_3(s$$), given $$S^\circ$$[Fe(s)] = 27.23 J mol$$^{-1} K$^{-1}$$, $$S^\circ$$[O$$_2(g$$)] = 205 J mol$$^{-1} K$^{-1}$$, $$S^\circ$$[Fe$$_2O$_3(s$$)] = 87.4 J mol$$^{-1} K$^{-1}.$$

Accepted Answer

$$\Delta S^\circ = 2 	imes 87.4 - [4 	imes 27.23 + 3 	imes 205] = -549.5 J $$mol$$^{-1} K$^{-1}$$

Question 13

Which of the following changes will always increase the entropy of a system?

Accepted Answer

Dissolving a salt in water

Question 14

For the reaction: 2SO$$_2(g) + O$_2(g$$) → 2SO$$_3(g$$), given $$\Delta G_f^\circ(SO$_2) = -300.4 kJ/$$mol and $$\Delta G_f^\circ(SO$_3) = -370.4 kJ/$$mol, what is $$\Delta G^\circ$$ for the reaction?

Accepted Answer

$$\Delta G^\circ = 2 	imes (-370.4) - [2 	imes (-300.4) + (-1) 	imes 0] = -139.2 kJ$$

Question 15

At what temperature does the decomposition of CaCO$$_3$$ become spontaneous, given $$\Delta H^\circ = 178.3 kJ/$$mol and $$\Delta S^\circ = 159.0 J/K$$·mol?

Accepted Answer

$$T = \frac{178.3}{0.159} = 1122 K$$

Question 16

Which of the following best describes the relationship between the standard Gibbs free energy change ($$\Delta G^\circ) $$and the equilibrium constant ($$K$$)?

Accepted Answer

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

Question 17

If $$\Delta G^\circ$$ for a reaction is large and positive, what can you conclude about the equilibrium constant $$K$$?

Accepted Answer

$$0 \u003c K \u003c 1$$

Question 18

A reaction has $$\Delta H = 100 kJ/$$mol and $$\Delta S = 0.25 kJ/K$$·mol. At what temperature does the reaction become spontaneous?

Accepted Answer

$$T = \frac{100}{0.25} = 400 K$$

Question 19

Which of the following is NOT a factor that increases the entropy of a system?

Accepted Answer

Decreasing molecular complexity

Chapter 19: Chemical Thermodynamics – Study Notes

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