Question 1

Which of the following statements best describes the relationship between the equilibrium constant $$K$$ and the standard Gibbs free energy change $$\Delta_r G^\circ$$ for a reaction at temperature $$T$$?

Accepted Answer

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

Question 2

A reaction has $$\Delta_r G^\circ = +35 kJ $$mol$$^{-1} at 298 K. $$What can you conclude about the equilibrium constant $$K$$ and the position of equilibrium at room temperature?

Accepted Answer

The equilibrium constant $$K is $$much less than 1; reactants are strongly favored.

Question 3

Consider the following equilibrium: $$\mathrm{N_2O_4(g)} \rightleftharpoons 2\mathrm{NO_2$(g)}. If $$the volume of the reaction vessel is decreased at constant temperature, what will happen to the position of equilibrium?

Accepted Answer

The equilibrium will shift toward $$\mathrm{N_2O_4} ($$the side with fewer moles of gas).

Question 4

Which of the following changes will NOT affect the position of equilibrium for a gaseous reaction mixture?

Accepted Answer

Adding an inert gas at constant volume.

Question 5

For the reaction $$\mathrm{A(g) + B(g) \rightleftharpoons C(g)}$$, $$\Delta_r H^\circ is $$positive. Which of the following will increase the equilibrium concentration of $$\mathrm{C}$$?

Accepted Answer

Increasing the temperature.

Question 6

A catalyst is added to a reaction mixture at equilibrium. What is the effect on the equilibrium position and the rate at which equilibrium is achieved?

Accepted Answer

The position of equilibrium is unchanged, but equilibrium is reached more quickly.

Question 7

Which of the following best describes an exothermic reaction?

Accepted Answer

$$\Delta H \u003c 0$$; heat is released to the surroundings.

Question 8

A reaction mixture is at equilibrium. If more product is added, what will happen to the value of the reaction quotient $$Q$$ and the direction in which the reaction will proceed?

Accepted Answer

$$Q$$ increases and the reaction shifts toward reactants.

Question 9

At what temperature does the phase change between ice and liquid water occur, and what is true about the Gibbs free energy at this point?

Accepted Answer

At $$0^\circC$$, $$\Delta G = 0$$ for the phase change.

Question 10

Which of the following statements about entropy ($$S) is $$correct?

Accepted Answer

An increase in entropy ($$\Delta S \u003e 0) $$tends to favor spontaneity.

Question 11

Consider the reaction $$\mathrm{2SO_2(g) + O_2$(g) \rightleftharpoons 2SO_3(g)}. If $$the volume of the container is increased, what will happen to the equilibrium position?

Accepted Answer

The equilibrium will shift toward the side with more moles of gas (reactants).

Question 12

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

Accepted Answer

$$\Delta G = 0$$

Question 13

A reaction has $$\Delta H = +50 kJ $$mol$$^{-1}$$ and $$\Delta S = +100 J K$^{-1}$$ mol$$^{-1}. At $$what temperature will the reaction become spontaneous?

Accepted Answer

At temperatures above $$500 K.$$

Question 14

Which of the following best explains why increasing temperature favors the products in an endothermic reaction?

Accepted Answer

Because $$K$$ increases as temperature increases for endothermic reactions.

Question 15

If $$Q \u003c K$$ for a reaction mixture, what will happen as the system moves toward equilibrium?

Accepted Answer

The reaction will proceed in the forward direction to form more products.

Question 16

Which of the following is a correct statement of Le Châtelier’s principle?

Accepted Answer

If a system at equilibrium is disturbed, it will shift in the direction that counteracts the disturbance.

Question 17

Which of the following changes will increase the value of the equilibrium constant $$K$$ for an exothermic reaction?

Accepted Answer

Decreasing the temperature.

Question 18

A reaction is spontaneous at room temperature. Which of the following must be true?

Accepted Answer

$$\Delta G \u003c 0$$

Question 19

Which of the following best describes the effect of removing a reactant from a system at equilibrium?

Accepted Answer

The reaction will shift toward the reactants to counteract the change.

Question 20

Which of the following is true regarding the effect of a catalyst on a chemical equilibrium?

Accepted Answer

A catalyst increases the rate at which equilibrium is achieved but does not change the equilibrium position.

Equilibrium, Gibbs Free Energy, and Response to Changes in Chemical Systems

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