Question 1

For the reaction $$\mathrm{N_2O_4(g) \rightleftharpoons 2 NO_2$(g)}$$, what will happen to the concentrations of $$\mathrm{NO_2$}$$ and $$\mathrm{N_2O_4} if $$additional $$\mathrm{NO_2$} is $$added to a system at equilibrium?

Accepted Answer

The concentration of $$\mathrm{NO_2$}$$ will decrease and $$\mathrm{N_2O_4}$$ will increase until a new equilibrium is established.

Question 2

According to Le Châtelier’s principle, what is the effect of removing a reactant from a system at equilibrium?

Accepted Answer

The equilibrium shifts toward the reactants to produce more of the removed reactant.

Question 3

For the reaction $$\mathrm{N_2$(g) + 3 H_2$(g) \rightleftharpoons 2 NH_3$(g)}$$, what will happen if the volume of the reaction vessel is decreased at constant temperature?

Accepted Answer

The equilibrium will shift toward the side with fewer moles of gas, producing more $$\mathrm{NH_3$}.$$

Question 4

Which of the following changes will NOT affect the position of equilibrium for a gas-phase reaction?

Accepted Answer

Adding an inert gas at constant volume.

Question 5

For the exothermic reaction $$\mathrm{2 NO(g) + Cl_2$(g) \rightleftharpoons 2 NOCl(g)}$$, which change will shift the equilibrium to the right?

Accepted Answer

Decreasing the temperature.

Question 6

A reaction at equilibrium is disturbed by removing some product. What is the immediate effect on the rates of the forward and reverse reactions?

Accepted Answer

The rate of the reverse reaction decreases, while the rate of the forward reaction is initially unchanged.

Question 7

For the endothermic reaction $$\mathrm{N_2O_4(g) + heat \rightleftharpoons 2 NO_2$(g)}$$, what happens to the equilibrium constant $$K if $$the temperature is increased?

Accepted Answer

$$K$$ increases.

Question 8

A chemical plant wants to maximize the yield of ammonia in the Haber process: $$\mathrm{N_2$(g) + 3 H_2$(g) \rightleftharpoons 2 NH_3$(g)}. $$Which of the following strategies would be most effective?

Accepted Answer

Decrease the temperature and decrease the volume.

Question 9

Which of the following statements about equilibrium is correct?

Accepted Answer

At equilibrium, the rates of the forward and reverse reactions are equal.

Question 10

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

Accepted Answer

The equilibrium will shift toward the side with more moles of gas, producing more $$\mathrm{SO_2$}$$ and $$\mathrm{O_2$}.$$

Question 11

A reaction mixture at equilibrium is subjected to a decrease in temperature. The reaction is exothermic. What is the effect on the equilibrium constant $$K$$?

Accepted Answer

$$K$$ increases.

Question 12

For the reaction $$\mathrm{N_2O_4(g) \rightleftharpoons 2 NO_2$(g)}$$, which of the following will NOT change the value of the equilibrium constant $$K$$?

Accepted Answer

Adding more $$\mathrm{NO_2$}.$$

Question 13

A student adds an inert gas to a reaction mixture at equilibrium in a rigid container. What is the effect on the equilibrium position?

Accepted Answer

There is no effect on the equilibrium position.

Question 14

Which of the following best describes the effect of adding a catalyst to a system at equilibrium?

Accepted Answer

It has no effect on the position of equilibrium or the value of $$K.$$

Question 15

A reaction at equilibrium is represented by $$\mathrm{A(g) + B(g) \rightleftharpoons 2C(g)}. If $$the total pressure is increased by decreasing the volume, what will happen to the equilibrium position?

Accepted Answer

The equilibrium will shift toward the side with fewer moles of gas.

Question 16

For the reaction $$\mathrm{2 NO_2$(g) \rightleftharpoons N_2O_4(g)}$$, what is the effect of removing $$\mathrm{N_2O_4}$$ from the system at equilibrium?

Accepted Answer

The equilibrium will shift to the right to produce more $$\mathrm{N_2O_4}.$$

Question 17

A reaction at equilibrium is subjected to a sudden increase in temperature. The reaction is endothermic. What will happen to the concentrations of products and reactants?

Accepted Answer

The concentration of products will increase and the concentration of reactants will decrease.

Question 18

Which of the following is a correct application of Le Châtelier’s principle in a real-world scenario?

Accepted Answer

Removing ammonia as it forms in the Haber process drives the reaction to produce more ammonia.

Chemical Equilibrium and Le Châtelier’s Principle: Effects of Concentration, Volume, and Temperature

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