Q: For the reaction $$2 Ca(s) + O_2$(g) \rightarrow 2 CaO(s)$$, $$\Delta H_{rxn} = -1269.8 kJ $$and $$\Delta S_{rxn} = -363.6 J/K. At $$what temperature does the reaction change from spontaneous to nonspontaneous?

$$T = \frac{\Delta H}{\Delta S} = \frac{-1269.8 \text{ kJ}}{-0.3636 \text{ kJ/K}} = 3492 K$$

Question 1

Which of the following statements best describes a spontaneous process?

Accepted Answer

A process that occurs without ongoing outside intervention.

Question 2

The conversion of diamond to graphite is spontaneous but extremely slow. What does this indicate about the relationship between thermodynamics and kinetics?

Accepted Answer

A reaction can be thermodynamically spontaneous but kinetically slow.

Question 3

Which of the following best explains why ice melts spontaneously at temperatures above 0°C, even though the process is endothermic?

Accepted Answer

The increase in entropy ($$\Delta S) of $$the system outweighs the positive enthalpy change ($$\Delta H).$$

Question 4

According to the second law of thermodynamics, which of the following must be true for a process to be spontaneous?

Accepted Answer

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

Question 5

Which equation correctly relates entropy to the number of microstates ($$W) in a $$system?

Accepted Answer

$$S = k_B \ln W$$

Question 6

For the reaction $$C_3H_8(g) + 5 O_2$(g) \rightarrow 3 CO_2$(g) + 4 H_2O(g)$$ with $$\Delta H = -2044 kJ at 25$$°C, what is the entropy change of the surroundings ($$\Delta S_{surr}$$)?

Accepted Answer

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

Question 7

Which of the following processes results in an increase in entropy?

Accepted Answer

Dissolving NaCl(s) in water to form NaCl(aq)

Question 8

Given $$\Delta H = +100 kJ $$and $$\Delta S = +750 J/K $$for a reaction, at what temperature does the reaction become spontaneous?

Accepted Answer

$$T \u003e 133 K$$

Question 9

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

Accepted Answer

$$\Delta G = 0$$

Question 10

Calculate the standard entropy change ($$\Delta S^\circ_{rxn}) $$for the reaction $$CCl_4(g$$) \rightarrow C(s) + 2Cl_2(g)$$ given S$$^\circ($$CCl_4) = 214.39$ J/mol·K, S$$^\circ(C) = 5.69$$ J/mol·K, S$$^\circ($$Cl_2) = 223.08$ J/mol·K.

Accepted Answer

$$237.46 J/K$$

Question 11

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

Accepted Answer

The entropy of a perfect crystal at absolute zero is zero.

Question 12

Which of the following reactions will have the largest equilibrium constant ($$K) at 298 K$$?

Accepted Answer

2 Hg(g) + $$O_2(g$$) \rightarrow 2 HgO(s), \Delta G^\circ = -180.8$ kJ

Question 13

For the reaction $$2 Ca(s) + O_2$(g) \rightarrow 2 CaO(s)$$, $$\Delta H_{rxn} = -1269.8 kJ $$and $$\Delta S_{rxn} = -363.6 J/K. At $$what temperature does the reaction change from spontaneous to nonspontaneous?

Accepted Answer

$$T = \frac{\Delta H}{\Delta S} = \frac{-1269.8 	ext{ kJ}}{-0.3636 	ext{ kJ/K}} = 3492 K$$

Question 14

Which of the following factors increases the entropy of a system?

Accepted Answer

Increasing temperature

Question 15

Which of the following gases has the highest standard molar entropy?

Accepted Answer

Xe(g)

Question 16

For a reaction, $$\Delta H = +35.5 kJ/$$mol and $$\Delta S = +83.6 J/$$mol·K. At what temperature does the reaction become spontaneous?

Accepted Answer

$$T \u003e 425 K$$

Question 17

Which of the following best describes the relationship between $$\Delta G$$ and the equilibrium constant $$K$$?

Accepted Answer

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

Question 18

A reaction has an equilibrium constant $$K \u003c 1. $$What can you conclude about $$\Delta G^\circ$$ for the reaction?

Accepted Answer

$$\Delta G^\circ \u003e 0$$

Question 19

Which of the following scenarios best illustrates an increase in entropy?

Accepted Answer

A child’s room becoming messier over time

Chapter 19: Free Energy and Thermodynamics – Study Notes

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