Question 1

Which of the following statements best describes a spontaneous process?

Accepted Answer

A process that occurs under a specific set of conditions without ongoing outside intervention.

Question 2

Which of the following changes will result in an increase in the entropy ($$S) of a $$system?

Accepted Answer

Dissolving sodium chloride in water.

Question 3

Given the reaction: $$\mathrm{$$CaCO_3$$(s) \rightarrow CaO(s) + CO_2$(g)}$$, and the following standard molar entropies: $$S^\circ[\mathrm{$$CaCO_3$$(s)}] = 92.9\ \mathrm{J/K\cdot mol}$$, $$S^\circ[\mathrm{CaO(s)}] = 39.8\ \mathrm{J/K\cdot mol}$$, $$S^\circ[\mathrm{CO_2$(g)}] = 213.6\ \mathrm{J/K\cdot mol}$$, calculate $$\Delta S^\circ_{rxn}$$ for the reaction at $$25^\circC.$$

Accepted Answer

$$\Delta S^\circ_{rxn} = 160.5\ \mathrm{J/K\cdot mol}$$

Question 4

Which of the following best explains why exothermicity alone does not guarantee spontaneity?

Accepted Answer

Some exothermic reactions have a negative entropy change, making $$\Delta G$$ positive at certain temperatures.

Question 5

The entropy change for the surroundings ($$\Delta S_{surr}) is $$most directly related to which thermodynamic quantity?

Accepted Answer

The enthalpy change of the system ($$\Delta H_{sys})$$

Question 6

Which of the following processes is expected to have a negative entropy change ($$\Delta S \u003c 0$$)?

Accepted Answer

Condensation of water vapor on a cold surface

Question 7

According to the Third Law of Thermodynamics, what is the entropy of a perfect crystalline substance at absolute zero ($$0\ \mathrm{K}$$)?

Accepted Answer

$$S = 0$$

Question 8

For the reaction $$\mathrm{2MgO(s) \rightarrow 2Mg(s) + O_2$(g)}$$, given $$\Delta G_f^\circ[\mathrm{MgO(s)}] = -569.6\ \mathrm{kJ/mol}$$, $$\Delta G_f^\circ[\mathrm{Mg(s)}] = 0$$, and $$\Delta G_f^\circ[\mathrm{O_2$(g)}] = 0$$, what is $$\Delta G^\circ_{rxn} at$$ $$25^\circC$$?

Accepted Answer

$$\Delta G^\circ_{rxn} = 1139.2\ \mathrm{kJ}$$

Question 9

Which equation correctly relates the standard free energy change ($$\Delta G^\circ) to $$the equilibrium constant ($$K) at $$temperature $$T$$?

Accepted Answer

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

Question 10

A reaction has $$\Delta H = 199.5\ \mathrm{kJ/mol}$$ and $$\Delta S = 0.476\ \mathrm{kJ/K\cdot mol}. $$Above what temperature (in $$^\circC) $$does the reaction become spontaneous?

Accepted Answer

$$146^\circ\mathrm{C}$$

Question 11

Which of the following best describes the relationship between $$\Delta G$$ and spontaneity at constant temperature and pressure?

Accepted Answer

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

Question 12

A sample of 1.0 mol of an ideal gas expands isothermally from $$2.5\ \mathrm{L} to$$ $$5.0\ \mathrm{L} at$$ $$25^\circC. $$What is the entropy change ($$\Delta S) $$for the gas? ($$R = 8.314\ \mathrm{J/K\cdot mol})$$

Accepted Answer

$$\Delta S = 5.8\ \mathrm{J/K}$$

Question 13

Which of the following reactions will have a positive entropy change ($$\Delta S^\circ_{rxn} \u003e 0$$)?

Accepted Answer

$$\mathrm{$$CaCO_3$$(s) \rightarrow CaO(s) + CO_2$(g)}$$

Question 14

The standard entropy of $$\mathrm{Na(s)} at$$ $$25^\circC is$$ $$51.05\ \mathrm{J/K\cdot mol}$$, and that of $$\mathrm{Na(l)} is$$ $$57.56\ \mathrm{J/K\cdot mol}. $$What is the sign of $$\Delta S$$ for the melting of sodium at its melting point?

Accepted Answer

Positive

Question 15

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

Accepted Answer

The reaction becomes more spontaneous as temperature increases.

Question 16

For the reaction $$\mathrm{H_2O(l) ightarrow H_2$(g) + 1/2 O_2$(g)} at$$ $$25^\circC$$, $$\Delta G^\circ = 474.4\ \mathrm{kJ/mol}. $$What is the equilibrium constant $$K$$ for this reaction at $$25^\circC$$? ($$R = 8.314 	imes 10$$^{-3}$$\ \mathrm{kJ/K\cdot mol}$$, $$T = 298\ \mathrm{K})$$

Accepted Answer

$$K = 7 	imes 10$$^{-84}$$

Question 17

Which of the following statements about the standard free energy of formation ($$\Delta G_f^\circ) is $$correct?

Accepted Answer

$$\Delta G_f^\circ$$ for any element in its standard state is zero.

Question 18

A chemical reaction at $$25^\circC $$has $$\Delta G^\circ = 0. $$What can be concluded about the equilibrium constant $$K$$ for this reaction?

Accepted Answer

$$K = 1$$

Entropy, Free Energy, and Chemical Equilibrium – Chapter 18 Study Notes

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