Question 1

Which of the following best describes dynamic equilibrium in a chemical reaction?

Accepted Answer

The rates of the forward and reverse reactions are equal, so no net change is observed macroscopically.

Question 2

For the reaction $$\mathrm{N_2O_4(g) \rightleftharpoons 2NO_2(g)}$$, the equilibrium constant expression is:

Accepted Answer

$$K = \dfrac{[NO_2$]^2}{[N_2O_4]}$$

Question 3

If $$K \ll 1$$ for a reaction, what does this indicate about the equilibrium mixture?

Accepted Answer

The reaction favors the reactants.

Question 4

Given the reaction $$aA + bB \rightleftharpoons cC + dD$$, the reaction quotient $$Q is$$:

Accepted Answer

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

Question 5

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

Accepted Answer

$$K is $$only valid at equilibrium and at a specific temperature.

Question 6

For the heterogeneous equilibrium $$\mathrm{$$CaCO_3$$(s) \rightleftharpoons CaO(s) + CO_2$(g)}$$, the equilibrium constant expression is:

Accepted Answer

$$K = [CO_2$]$$

Question 7

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

Accepted Answer

The reaction will shift to the right, forming more products.

Question 8

Which of the following is NOT included in the equilibrium constant expression for a heterogeneous equilibrium?

Accepted Answer

Pure solids

Question 9

A reaction has $$K = 1. $$What does this indicate about the equilibrium concentrations of reactants and products?

Accepted Answer

Reactants and products are present in roughly equal amounts at equilibrium.

Question 10

Which of the following best explains why chemical equilibrium is described as 'dynamic'?

Accepted Answer

The forward and reverse reactions continue to occur at equal rates.

Question 11

For the reaction $$\mathrm{N_2O_4(g) \rightleftharpoons 2NO_2(g)}$$, if the initial concentration of $$\mathrm{NO_2$} is $$much higher than $$\mathrm{N_2O_4}$$, what will happen as the system approaches equilibrium?

Accepted Answer

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

Question 12

Which of the following changes will NOT affect the value of the equilibrium constant $$K$$ for a given reaction?

Accepted Answer

Adding more reactant

Question 13

A student mixes $$\mathrm{N_2O_4}$$ and $$\mathrm{NO_2$} in a $$closed container. After some time, the concentrations of both gases remain constant. What can be concluded?

Accepted Answer

The system has reached equilibrium.

Question 14

For the reaction $$\mathrm{aA + bB \rightleftharpoons cC + dD}$$, which of the following would increase the value of $$K$$?

Accepted Answer

Increasing the temperature for an endothermic reaction

Question 15

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

Accepted Answer

It increases the rate at which equilibrium is achieved but does not change $$K.$$

Question 16

A reaction mixture has $$Q \u003e K. $$What will happen as the system moves toward equilibrium?

Accepted Answer

The reaction will shift to the left, forming more reactants.

Question 17

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

Accepted Answer

The rates of the forward and reverse reactions are equal.

Question 18

In a closed system, the color of a gas mixture changes from colorless to brown and then remains constant. What does this indicate about the chemical system?

Accepted Answer

The system has reached equilibrium.

Question 19

For the reaction $$\mathrm{N_2O_4(g) \rightleftharpoons 2NO_2(g)}$$, which of the following would NOT be a valid way to change the value of $$K$$?

Accepted Answer

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

Chemical Equilibrium: The Extent of Chemical Reactions

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