Q: Calculate the free energy change for this reaction at 25°C. Is the reaction spontaneous? $$C_6H_{12}(l) + 6 O_2$(g) \rightarrow 6 CO_2$(g) + 6 H_2O(l)$$, $$\Delta H$$^{\circ}$$_{rxn} = -3271.7 kJ$$, $$\Delta S$$^{\circ}$$_{rxn} = 101.1 J/K$$

$$-3.30 \times 10^3$ kJ; spontaneous

Question 1

Which of the following processes results in a decrease in entropy ($$\Delta S \u003c 0$$)?

Accepted Answer

The phase transition from a gas to a liquid

Question 2

Without doing any calculations, determine the sign of $$\Delta S_{sys}$$ for the chemical reaction: $$2 	ext{H}_2(g) + O_2$(g) ightarrow 2 	ext{H}_2O(g)$$

Accepted Answer

$$\Delta S is $$negative because 3 moles of gas are being converted into 2 moles of gas

Question 3

Calculate the change in entropy that occurs in the system when 47.0 g of water vaporizes at 100.0°C at its boiling point ($$\Delta H_{vap} = 40.7 kJ/$$mol).

Accepted Answer

$$131 J/K$$

Question 4

Without doing any calculations, determine the signs of $$\Delta S_{sys}$$ and $$\Delta S_{surr}$$ for the reaction: $$2 	ext{NH}_3(g) + O_2$(g) ightarrow 2 	ext{NO}(g) + 3 	ext{H}_2O(g) at $$high temperature.

Accepted Answer

$$\Delta S_{sys} \u003e 0$$, $$\Delta S_{surr} \u003c 0$$; spontaneous at high temperatures

Question 5

Given the values of $$\Delta H$$^{\circ}$$_{rxn}$$, $$\Delta S$$^{\circ}$$_{rxn}$$, and $$T$$, determine $$\Delta G_{rxn}$$ and predict whether or not the reaction is spontaneous: $$\Delta H$$^{\circ}$$_{rxn} = +125 kJ$$, $$\Delta S$$^{\circ}$$_{rxn} = -275 J/K$$, $$T = 378 K.$$

Accepted Answer

$$+45.5 kJ$$; nonspontaneous

Question 6

Consider a reaction that has a positive $$\Delta H$$ and a positive $$\Delta S. $$Which of the following statements is TRUE?

Accepted Answer

This reaction will be spontaneous only at high temperatures.

Question 7

Consider a reaction that has a negative $$\Delta H$$ and a positive $$\Delta S. $$Which of the following statements is TRUE?

Accepted Answer

This reaction will be spontaneous at all temperatures.

Question 8

Consider a reaction that has a positive $$\Delta H$$ and a negative $$\Delta S. $$Which of the following statements is TRUE?

Accepted Answer

This reaction will be nonspontaneous at all temperatures.

Question 9

Consider a reaction that has a negative $$\Delta H$$ and a negative $$\Delta S. $$Which of the following statements is TRUE?

Accepted Answer

This reaction will be spontaneous only at low temperatures.

Question 10

Above what temperature does the following reaction become nonspontaneous? $$	ext{Fe}_2O_3(s) + 3	ext{CO}(g) ightarrow 2	ext{Fe}(s) + 3	ext{CO}_2(g)$$, $$\Delta H = +11.0 kJ$$, $$\Delta S = +17.4 J/K$$

Accepted Answer

$$632 K$$

Question 11

Calculate the free energy change for this reaction at 25°C. Is the reaction spontaneous? $$C_6H_{12}(l) + 6 O_2$(g) \rightarrow 6 CO_2$(g) + 6 H_2O(l)$$, $$\Delta H$$^{\circ}$$_{rxn} = -3271.7 kJ$$, $$\Delta S$$^{\circ}$$_{rxn} = 101.1 J/K$$

Accepted Answer

$$-3.30 	imes 10^3$ kJ; spontaneous

Question 12

Place the following in order of increasing entropy at 298 K: He, Xe, Rn, Ar, Kr.

Accepted Answer

He \u003c Ar \u003c Kr \u003c Xe \u003c Rn

Question 13

Following in order of decreasing molar entropy at 298 K: NO, CO, SO.

Accepted Answer

SO \u003e NO \u003e CO

Question 14

Place the following in order of decreasing standard molar entropy: $$H_2O(g)$$, $$H_2O(l)$$, $$H_2O(s).$$

Accepted Answer

$$H_2O(g) \u003e H_2O(l) \u003e H_2O(s)$$

Question 15

Place the following in order of increasing standard molar entropy: $$NO_2(g$$)$$, N_2O_4(g$$)$$.

Accepted Answer

$$N_2O_4(g) \u003c NO_2$(g)$$

Question 16

Calculate $$\Delta S$$^{\circ}$$_{rxn}$$ for the following reaction. The $$S^{\circ}$$ for each species is shown below the reaction. $$C_2H_2(g) + H_2$(g) \rightarrow C_2H_4(g)$$, $$S^{\circ}$$ [J/mol·K]: $$200.9$$, $$130.7$$, $$219.3$$

Accepted Answer

$$-12.3 J/K$$

Question 17

Which substance has the higher standard molar entropy ($$S^{\circ}) at 25$$°C? $$Cl_2$$, $$NO_2 (g$$), $$Ar (g$$), $$C_6H_{12} (l$$), $$NaNO_3 (s)$$

Accepted Answer

$$NO_2 (g)$$

Question 18

Identify the compound with the lowest $$\Delta G$$^{\circ}$$_f.$$

Accepted Answer

$$N_2(g$$)$$

Question 19

Calculate $$\Delta G$$^{\circ}$$_{rxn}$$ using the following information: $$2H_2(g) + 3O_2(g) \rightarrow 2SO_2(g) + 2H_2O(g)$$, $$\Delta G$$^{\circ}$$_f$$ [kJ/mol]: $$SO_2(g) = -300.4$, H_2O(g) = -228.6$, H_2$(g) = 0$$, $$O_2(g) = 0$

Accepted Answer

$$-1057.2 kJ$$

Question 20

Use Hess's law to calculate $$\Delta G$$^{\circ}$$_{rxn}$$ using the following information: $$NO(g) + O_2$(g) \rightarrow NO_2$(g)$$, $$2NO_2(g) \rightarrow 2NO(g) + O_2$(g)$$, $$\Delta G$$^{\circ}$$_{rxn} = +68.4 kJ$$, $$2NO(g) + O_2$(g) \rightarrow 2NO_2(g)$$, $$\Delta G$$^{\circ}$$_{rxn} = -66.4 kJ$$

Accepted Answer

$$+2.0 kJ$$

Chapter 18: Thermodynamics – Practice and Study Guide

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