Q: Which equation correctly relates the entropy change of the surroundings to the enthalpy change of the system?

$$\Delta S_{\text{surr}} = \frac{-\Delta H_{\text{sys}}}{T}$$

Q: Calculate the change in entropy for the system when 1.00 mol of methanol (CH$$_3OH) $$vaporizes at its boiling point (64.6°C). $$\Delta H_{\text{vap}} = 35.2 kJ/$$mol.

$$\Delta S = \frac{35.2\,\text{kJ}}{337.75\,\text{K}} = 104.2\,\text{J/K}$$

Q: For the reaction $$\text{C(s, graphite)} + 2 \text{H}_2(g) \rightarrow \text{CH}_4(g)$$, $$\Delta H_{\text{rxn}} = -74.6 kJ$$, $$\Delta S_{\text{rxn}} = -80.8 J/K. At 298 K$$, what is $$\Delta G_{\text{rxn}}$$?

$$\Delta G = -74.6\,\text{kJ} - (298\,\text{K})(-0.0808\,\text{kJ/K}) = -50.5\,\text{kJ}$$

Question 1

Which statement best describes the Second Law of Thermodynamics?

Accepted Answer

The entropy of the universe increases in a spontaneous process.

Question 2

A perfect crystal at 0 K has how many microstates and what is its entropy?

Accepted Answer

W = 1, S = 0

Question 3

Which equation correctly relates the entropy change of the surroundings to the enthalpy change of the system?

Accepted Answer

$$\Delta S_{	ext{surr}} = \frac{-\Delta H_{	ext{sys}}}{T}$$

Question 4

Which process will have the greatest increase in entropy?

Accepted Answer

Vaporization of liquid water to water vapor

Question 5

For the reaction $$A_2$$ \rightarrow 2A$$, what are the signs of $$\Delta H$$ and $$\Delta S$$?

Accepted Answer

$$\Delta H \u003e 0$$, \Delta S \u003e 0$

Question 6

Which statement is true regarding the sublimation of dry ice (solid CO$$_2$$)?

Accepted Answer

$$\Delta H is $$positive, $$\Delta S is $$positive, and $$\Delta G is $$negative at high temperature and positive at low temperature.

Question 7

Calculate the change in entropy for the system when 1.00 mol of methanol (CH$$_3OH) $$vaporizes at its boiling point (64.6°C). $$\Delta H_{	ext{vap}} = 35.2 kJ/$$mol.

Accepted Answer

$$\Delta S = \frac{35.2\,	ext{kJ}}{337.75\,	ext{K}} = 104.2\,	ext{J/K}$$

Question 8

Which of the following statements about Gibbs Free Energy is correct?

Accepted Answer

If $$\Delta G \u003c 0$$, the process is spontaneous.

Question 9

Which factor most strongly affects the entropy change of the surroundings during a chemical reaction?

Accepted Answer

The temperature of the surroundings

Question 10

For the reaction $$	ext{C(s, graphite)} + 2 	ext{H}_2(g) ightarrow 	ext{CH}_4(g)$$, $$\Delta H_{	ext{rxn}} = -74.6 kJ$$, $$\Delta S_{	ext{rxn}} = -80.8 J/K. At 298 K$$, what is $$\Delta G_{	ext{rxn}}$$?

Accepted Answer

$$\Delta G = -74.6\,	ext{kJ} - (298\,	ext{K})(-0.0808\,	ext{kJ/K}) = -50.5\,	ext{kJ}$$

Question 11

Which trend in standard entropy is correct?

Accepted Answer

Gases have higher entropy than liquids.

Question 12

Which equation defines the change in entropy for a reversible process?

Accepted Answer

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

Question 13

Which scenario will result in a decrease in the entropy of the system?

Accepted Answer

Condensing water vapor

Question 14

Which statement about endothermic and exothermic processes is correct?

Accepted Answer

An exothermic process increases the entropy of the surroundings.

Question 15

Which of the following best describes a spontaneous process?

Accepted Answer

A process that occurs when $$\Delta G \u003c 0.$$

Question 16

Which of the following is true for the dissolution of KClO$$_3 in $$water?

Accepted Answer

The entropy of the system increases.

Question 17

Which factor increases the standard molar entropy of a substance?

Accepted Answer

Increasing the number of bonds

Question 18

For the reaction $$4	ext{NH}_3(g) + 5	ext{O}_2(g) ightarrow 4	ext{NO}(g) + 6	ext{H}_2	ext{O}(g)$$, calculate $$\Delta S_{	ext{rxn}}$$ using the following values: $$S^\circ(NH$_3) = 192.8 J/$$mol·K, $$S^\circ(O$_2) = 205.2 J/$$mol·K, $$S^\circ(NO) = 210.8 J/$$mol·K, $$S^\circ(H$_2O) = 188.8 J/$$mol·K.

Accepted Answer

$$\Delta S_{	ext{rxn}} = [4 	imes 210.8 + 6 	imes 188.8] - [4 	imes 192.8 + 5 	imes 205.2] = 120.4\,	ext{J/K}$$

Entropy Change During Vaporization of Methanol

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