Question 1

Which of the following best describes the role of temperature in determining the directionality of a chemical reaction, according to the Gibbs free energy equation $$\Delta G_{rxn} = \Delta H_{rxn} - T \Delta S_{rxn}$$?

Accepted Answer

Temperature determines whether the entropic or enthalpic factor dominates, so some reactions are product-favored only at high or low temperatures.

Question 2

Consider the reaction: $$2 	ext{CO}(g) + 	ext{O}_2(g) ightarrow 2 	ext{CO}_2(g). $$Using the following data: $$\Delta H_f^\circ(	ext{CO}) = -110.5 kJ/$$mol, $$\Delta H_f^\circ(	ext{CO}_2) = -393.5 kJ/$$mol$$, S^\circ(	ext{CO}) = 197.5 J/($$mol K), $$S^\circ(	ext{CO}_2) = 213.7 J/($$mol K), $$S^\circ(	ext{O}_2) = 205.0 J/($$mol K). Calculate $$\Delta H_{rxn}^\circ$$ for the reaction.

Accepted Answer

$$-566.0 kJ$$

Question 3

A reaction has $$\Delta H_{rxn} \u003c 0$$ and $$\Delta S_{rxn} \u003c 0. $$Under what temperature conditions will this reaction be product-favored?

Accepted Answer

At low temperatures

Question 4

For the reaction $$	ext{N}_2	ext{O}_4(g) ightleftharpoons 2 	ext{NO}_2(g)$$, $$\Delta H_{rxn}^\circ = 52.7 kJ $$and $$\Delta S_{rxn}^\circ = 176.9 J/K. At $$what temperature (in K) does the reaction become product-favored ($$\Delta G_{rxn} = 0$$)?

Accepted Answer

$$298 K$

Question 5

Which of the following statements about the equilibrium constant $$K is $$correct?

Accepted Answer

The value of $$K is $$determined by the chemical nature of the reactants and products and the temperature.

Question 6

Given the reaction $$	ext{CH}_4(g) ightarrow 	ext{C}(s) + 2 	ext{H}_2(g)$$, with $$\Delta H_{rxn}^\circ = 74.8 kJ $$and $$\Delta S_{rxn}^\circ = 35.1 J/K$ at 950 K$$, calculate $$\Delta G_{rxn}^\circ at 950 K.$$

Accepted Answer

$$41.5 kJ$$

Question 7

Which of the following best explains why fireworks are an example of a product-favored process at all temperatures?

Accepted Answer

The reaction is exothermic and increases entropy.

Question 8

For the reaction $$	ext{CO}_2(g) + 4 	ext{H}_2(g) ightarrow 	ext{CH}_4(g) + 2 	ext{H}_2	ext{O}(l)$$, $$\Delta H_{rxn}^\circ = -252.7 kJ $$and $$\Delta S_{rxn}^\circ = -410.3 J/K. At $$what temperature does the reaction change from product-favored to reactant-favored?

Accepted Answer

$$615.7 K$$

Question 9

Which of the following is true about the relationship between $$\Delta G_{rxn}^\circ$$ and the equilibrium constant $$K$$?

Accepted Answer

$$\Delta G_{rxn}^\circ = -RT \ln(K)$$

Question 10

A reaction has $$\Delta H_{rxn} \u003e 0$$ and $$\Delta S_{rxn} \u003e 0. $$Which statement is correct?

Accepted Answer

The reaction is product-favored only at high temperatures.

Question 11

Which of the following is NOT a factor that affects the directionality and extent of a chemical reaction?

Accepted Answer

The color of the reactants

Question 12

For the reaction $$2 	ext{H}_2(g) + 	ext{O}_2(g) ightarrow 2 	ext{H}_2	ext{O}(g)$$, which of the following best describes the signs of $$\Delta H_{rxn}$$ and $$\Delta S_{rxn}$$?

Accepted Answer

$$\Delta H_{rxn} \u003c 0$$, $$\Delta S_{rxn} \u003c 0$$

Question 13

Which of the following is the correct expression for the equilibrium constant $$K_c$$ for the reaction $$aA + bB \rightleftharpoons cC + dD$$?

Accepted Answer

$$K_c = \frac{[C]^c [D]^d}{[A]^a [B]^b}$$

Question 14

Which of the following best describes the effect of increasing temperature on a reaction with $$\Delta H_{rxn} \u003e 0$$ and $$\Delta S_{rxn} \u003e 0$$?

Accepted Answer

The reaction becomes more product-favored as temperature increases.

Question 15

Which of the following is a correct statement about the standard enthalpy of formation ($$\Delta H_f^\circ) $$for an element in its standard state?

Accepted Answer

$$\Delta H_f^\circ is $$zero.

Question 16

Which of the following best explains why the reaction $$	ext{N}_2	ext{O}_4(g) ightarrow 2 	ext{NO}_2(g) is $$more product-favored at higher temperatures?

Accepted Answer

The reaction is endothermic and has a positive entropy change.

Question 17

Which of the following is the correct formula for calculating $$\Delta S_{rxn}^\circ$$ for a reaction?

Accepted Answer

$$\Delta S_{rxn}^\circ = \sum S^\circ_{products} - \sum S^\circ_{reactants}$$

Thermodynamics and Chemical Equilibrium: Predicting Chemical Change

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