Q: Calculate the total entropy change ($$\Delta S_{\text{total}}) $$for a reaction with $$\Delta S_{\text{sys}} = 2.7\ \mathrm{J/K}$$ and $$\Delta S_{\text{surr}} = -6.0\ \mathrm{J/K}. Is $$this reaction spontaneous?

$$\Delta S_{\text{total}} = -3.3\ \mathrm{J/K}$$; the reaction is not spontaneous.

Q: Methanol has a normal melting point of 64.7°C and an entropy of fusion of $$9.36\ \mathrm{J/K}. $$What is the enthalpy of fusion?

$$\Delta H_{\text{fus}} = 2.16\ \mathrm{kJ}$$

Question 1

Which of the following statements best describes a spontaneous process?

Accepted Answer

A process that occurs without ongoing outside intervention.

Question 2

Which of the following reactions is nonspontaneous under standard conditions?

Accepted Answer

Photosynthesis: $$6\ \mathrm{CO_2$} + 6\ \mathrm{H_2O} \rightarrow \mathrm{C_6H_{12}O_6$} + 6\ \mathrm{O_2$}$$

Question 3

According to the Second Law of Thermodynamics, which of the following is true?

Accepted Answer

The total entropy of the universe is increasing with the passage of time.

Question 4

Which of the following changes will most likely result in a positive $$\Delta S$$ for the system?

Accepted Answer

Sublimation of dry ice ($$\mathrm{CO_2$(s) \rightarrow CO_2$(g)}).$$

Question 5

Which of the following reactions produces a decrease in the entropy of the system?

Accepted Answer

$$\mathrm{CO_2$(g) + H_2O(l) \rightarrow H_2CO_3(aq)}$$

Question 6

Calculate the total entropy change ($$\Delta S_{	ext{total}}) $$for a reaction with $$\Delta S_{	ext{sys}} = 2.7\ \mathrm{J/K}$$ and $$\Delta S_{	ext{surr}} = -6.0\ \mathrm{J/K}. Is $$this reaction spontaneous?

Accepted Answer

$$\Delta S_{	ext{total}} = -3.3\ \mathrm{J/K}$$; the reaction is not spontaneous.

Question 7

Which of the following factors does NOT increase the entropy of a system?

Accepted Answer

Decreasing the number of molecular degrees of freedom.

Question 8

Given the following standard molar entropies at 25°C: $$\mathrm{N_2$(g)} = 191.5\ \mathrm{J/(mol\cdot K)}$$, $$\mathrm{O_2$(g)} = 205.0\ \mathrm{J/(mol\cdot K)}$$, $$\mathrm{NO_2$(g)} = 240.1\ \mathrm{J/(mol\cdot K)}$$, calculate $$\Delta S^\circ$$ for the reaction: $$\mathrm{N_2$(g) + 2\ O_2$(g) \rightarrow 2\ NO_2$(g)}.$$

Accepted Answer

$$\Delta S^\circ = -81.3\ \mathrm{J/K}$$

Question 9

Methanol has a normal melting point of 64.7°C and an entropy of fusion of $$9.36\ \mathrm{J/K}. $$What is the enthalpy of fusion?

Accepted Answer

$$\Delta H_{	ext{fus}} = 2.16\ \mathrm{kJ}$$

Question 10

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

Accepted Answer

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

Question 11

The Boltzmann equation for entropy is $$S = k \ln W. If a $$system has $$1.0 	imes 10$$^{23}$$ microstates, what is the entropy of the system? (k = 1.38$$ 	imes $$10^{-23}$$\ \mathrm{J/K}$$)

Accepted Answer

$$S = 3.17\ \mathrm{J/K}$$

Question 12

Which of the following is true if $$\Delta G$$ for a reaction is negative?

Accepted Answer

The reaction is spontaneous in the forward direction.

Question 13

For the reaction $$\mathrm{P_4$(s) + 5\ O_2$(g) \rightarrow P_4O_{10}(s)}$$, $$\Delta H^\circ = -2940\ \mathrm{kJ}$$ and $$\Delta S^\circ = -220.1\ \mathrm{J/K} at 25$$°C. Calculate $$\Delta G^\circ$$ for the reaction.

Accepted Answer

$$\Delta G^\circ = -2874\ \mathrm{kJ}$$

Question 14

Which of the following combinations of $$\Delta H$$ and $$\Delta S$$ will always result in a spontaneous reaction?

Accepted Answer

$$\Delta H  0$$

Question 15

A reaction has $$\Delta H = 111.4\ \mathrm{kJ}$$ and $$\Delta S = 219.0\ \mathrm{J/K}. At $$what temperature (in K) will the reaction become spontaneous?

Accepted Answer

$$T \u003e 509\ \mathrm{K}$$

Question 16

Given $$\Delta G^\circ = -RT \ln K$$, what is the equilibrium constant $$K at 25$$°C for a reaction with $$\Delta G^\circ = -34.2\ \mathrm{kJ/mol}$$? ($$R = 8.314\ \mathrm{J/(mol\cdot K)})$$

Accepted Answer

$$K = 1.2 	imes 10^6$

Question 17

For the reaction $$\mathrm{Fe_2O_3(s) + 3\ H_2$(g) \rightarrow 2\ Fe(s) + 3\ H_2O(g)}$$, calculate $$\Delta G^\circ at 25$$°C using the following values: $$\Delta G^\circ_f (Fe$_2O$_3$$) = $$-742.2\ \mathrm{kJ/mol}$$, $$\Delta G^\circ_f (H$_2O$$) = $$-228.6\ \mathrm{kJ/mol}.$$

Accepted Answer

$$\Delta G^\circ = 28.0\ \mathrm{kJ}$$

Question 18

A reaction has $$\Delta G^\circ = -374\ \mathrm{kJ}$$ and partial pressures of S$$_2$$, F$$_2$$, SF$$_6$$ are 0.80 atm, 0.95 atm, and 1.7 atm, respectively. Calculate $$\Delta G$$ for the reaction $$\mathrm{S_2$(g) + 3\ F_2$(g) \rightarrow 2\ SF_6$(g)} at 25$$°C.

Accepted Answer

$$\Delta G = -370\ \mathrm{kJ}$$

Ch.18 – Free Energy and Thermodynamics: Study Notes

Study Guide - Practice Questions

Study Guide - Flashcards