Question 1

Which of the following best describes what happens when a closed system containing $$\mathrm{N_2O_4(g)} is $$warmed, as shown in the first image?

Accepted Answer

The system turns brown as $$\mathrm{N_2O_4}$$ partially dissociates to form $$\mathrm{NO_2$}$$ gas, and equilibrium is established between $$\mathrm{N_2O_4}$$ and $$\mathrm{NO_2$}.$$

Question 2

Which statement about chemical equilibrium is supported by the second image (concentration and rate graphs)?

Accepted Answer

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

Question 3

For the reaction $$\mathrm{N_2O_4(g) \rightleftharpoons 2NO_2(g)}$$, which of the following is the correct expression for the equilibrium constant $$K_c$$?

Accepted Answer

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

Question 4

If $$K_c$$ for a reaction is much greater than 1, as shown in the third image, what does this indicate about the equilibrium mixture?

Accepted Answer

Products predominate at equilibrium.

Question 5

Given the reaction $$\mathrm{2NO_2(g) \rightleftharpoons N_2O_4(g)}$$ with $$K_c = 0.212 at$$ $$100^\circC$$, what is the equilibrium constant for the reverse reaction?

Accepted Answer

$$K_c = 4.72$$

Question 6

A mixture contains $$[NH_3$] = 98$$ atm, $$[N_2$] = 45$$ atm, and $$[H_2$] = 55$$ atm. If $$Q \u003e K$$ for the reaction $$\mathrm{N_2$(g) + 3H_2(g) \rightleftharpoons 2NH_3(g)}$$, which way will the reaction proceed to reach equilibrium?

Accepted Answer

The reaction will proceed to the left, forming more $$N_2$$ and $$H_2.$$

Question 7

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

Accepted Answer

Adding a catalyst.

Question 8

For the heterogeneous equilibrium $$\mathrm{$$CaCO_3$$(s) \rightleftharpoons CaO(s) + CO_2$(g)}$$, which is the correct expression for $$K_c$$?

Accepted Answer

$$K_c = [CO_2$]$$

Question 9

If the reaction quotient $$Q is $$less than the equilibrium constant $$K$$, as shown in the fourth image, what will happen?

Accepted Answer

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

Question 10

A closed vessel contains $$\mathrm{HI(g)} at $$equilibrium at $$425^\circC $$with $$[HI] = 3.53 	imes 10$$^{-3}$$ M, $$[$$H_2$$] = 4.79 	imes $$10^{-4} M$$, and $$[I_2$] = 4.79 	imes 10$$^{-4}$$ M. What is the value of K_c$ for the reaction $$\mathrm{2HI(g) ightleftharpoons $$H_2(g$$) + $$I_2(g$$)}$$?

Accepted Answer

$$K_c = \dfrac{[H_2$][I_2$]}{[HI]^2}$$

Question 11

According to Le Châtelier’s Principle (see the fifth image), what will happen if the pressure is increased on the equilibrium $$\mathrm{N_2$(g) + 3H_2(g) \rightleftharpoons 2NH_3(g)} by $$decreasing the volume?

Accepted Answer

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

Question 12

Which of the following best explains why a catalyst does not affect the equilibrium position of a reaction?

Accepted Answer

A catalyst increases the rate of both the forward and reverse reactions equally, lowering the activation energy for both.

Question 13

For the reaction $$\mathrm{2SO_2(g) + O_2$(g) \rightleftharpoons 2SO_3(g)}$$, what will happen if more $$SO_2 is $$added to the system at equilibrium?

Accepted Answer

The equilibrium will shift to the right, producing more $$SO_3.$$

Question 14

A reaction is exothermic. According to Le Châtelier’s Principle, what will happen if the temperature is increased?

Accepted Answer

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

Question 15

Which of the following statements is TRUE regarding the concentrations of reactants and products at equilibrium?

Accepted Answer

The concentrations of reactants and products remain constant over time.

Question 16

If a reaction mixture is not at equilibrium, how can you predict the direction in which the reaction will proceed?

Accepted Answer

By comparing the reaction quotient $$Q to $$the equilibrium constant $$K.$$

Question 17

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

Accepted Answer

Concentration of a pure solid.

Question 18

For the reaction $$\mathrm{A(g) + B(g) \rightleftharpoons C(g)}$$, $$K_c = 10. If$$ $$[A] = 0.2 M$$, $$[B] = 0.2 M$$, and $$[C] = 0.1 M$$, what is the value of $$Q$$ and which direction will the reaction proceed?

Accepted Answer

$$Q = 2.5$$, reaction proceeds to the right.

Question 19

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

Accepted Answer

The equilibrium shifts to produce more product.

Chemical Equilibrium: Principles, Constants, and Applications

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