Question 1

Which of the following best describes a chemical equilibrium?

Accepted Answer

The rates of the forward and reverse reactions are equal, so the concentrations of reactants and products remain constant.

Question 2

Consider the decomposition of dinitrogen tetraoxide: $$\mathrm{N_2O_4 (g) \rightleftharpoons 2NO_2 (g)}. If $$you start with only $$\mathrm{NO_2$} in a $$closed flask, what will happen over time?

Accepted Answer

The system will reach the same equilibrium mixture of $$\mathrm{N_2O_4}$$ and $$\mathrm{NO_2$} as if $$you had started with only $$\mathrm{N_2O_4}.$$

Question 3

Which statement about chemical equilibrium is FALSE?

Accepted Answer

At equilibrium, the concentrations of reactants and products are always equal.

Question 4

A student observes a salt solution where the amount of solid salt and dissolved ions appears unchanged over time. What is the best explanation for this observation?

Accepted Answer

The rates of salt dissolving and precipitating are equal, so the system is at equilibrium.

Question 5

Which of the following is a characteristic of a reversible reaction?

Accepted Answer

It can proceed in both the forward and reverse directions under the same conditions.

Question 6

In the reaction $$\mathrm{N_2O_4 (g) \rightleftharpoons 2NO_2 (g)}$$, what happens to the concentrations of $$\mathrm{N_2O_4}$$ and $$\mathrm{NO_2$} as $$equilibrium is approached from a starting sample of pure $$\mathrm{N_2O_4}$$?

Accepted Answer

The concentration of $$\mathrm{N_2O_4}$$ decreases and $$\mathrm{NO_2$}$$ increases until both become constant.

Question 7

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

Accepted Answer

Reactants and products are constantly being formed and consumed at equal rates.

Question 8

A chemist claims that at equilibrium, the amount of reactants and products must be equal. Is this correct? Why or why not?

Accepted Answer

No, because equilibrium means constant concentrations, not necessarily equal amounts.

Question 9

Which of the following scenarios best illustrates a system at chemical equilibrium?

Accepted Answer

A closed flask where the color of the gas mixture stops changing, but reactions continue at the molecular level.

Question 10

If the forward reaction in a reversible system is exothermic, what will happen to the equilibrium position if the temperature is increased?

Accepted Answer

The equilibrium will shift to favor the reverse reaction.

Question 11

Why is it possible for the equilibrium concentrations of reactants and products to be different, even though the rates of the forward and reverse reactions are equal?

Accepted Answer

Because the equilibrium position depends on the relative stabilities of reactants and products.

Question 12

A reaction is observed where the concentrations of reactants decrease rapidly at first, then level off and remain constant. What does this indicate?

Accepted Answer

The reaction has reached equilibrium.

Question 13

Which of the following is TRUE regarding the direction of approach to equilibrium?

Accepted Answer

The equilibrium concentrations are independent of the starting composition.

Question 14

In a closed system, the reaction $$\mathrm{A \rightleftharpoons B} is at $$equilibrium. If more $$\mathrm{A} is $$added, what will happen immediately?

Accepted Answer

The forward reaction rate will increase until a new equilibrium is established.

Question 15

A medical laboratory uses the equilibrium between dissolved and undissolved calcium salts to monitor kidney function. If the rates of dissolution and precipitation are equal, what does this indicate?

Accepted Answer

The system is at chemical equilibrium.

Chemical Equilibrium and Reversible Reactions

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