Q: A closed system initially contains $$1.000 \times 10$$^{-3}$$\ \mathrm{M}\ H_2$ and 2.000$$ \times $$10^{-3}$$\ \mathrm{M}\ $$I_2 at$$ $$448^\circC. At $$equilibrium, $$[HI] = 1.87 \times 10$$^{-3}$$\ \mathrm{M}. $$What is the equilibrium concentration of $$H_2$$?

$$6.5 \times 10$$^{-5}$$\ \mathrm{M}$$

Question 1

Which of the following best describes chemical equilibrium in a closed system?

Accepted Answer

The rates of the forward and reverse reactions are equal.

Question 2

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

Accepted Answer

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

Question 3

In the Haber process, $$\mathrm{N_2$(g) + 3H_2(g) \rightleftharpoons 2NH_3(g)}$$, what will happen to the equilibrium position if the pressure is increased?

Accepted Answer

It will shift toward the side with fewer moles of gas.

Question 4

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

Accepted Answer

If $$K \approx 1$$, significant amounts of both reactants and products are present at equilibrium.

Question 5

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

Accepted Answer

$$K_c = [CO_2$]$$

Question 6

If the equilibrium constant for a reaction is $$K_c = 0.212 at$$ $$100^\circC$$, what is the equilibrium constant for the reverse reaction?

Accepted Answer

$$K_c = 1/0.212$$

Question 7

A reaction mixture contains $$[A] = 0.10\ \mathrm{M}$$, $$[B] = 0.20\ \mathrm{M}$$, $$[C] = 0.30\ \mathrm{M}$$ for the reaction $$A + 2B \rightleftharpoons 3C. If$$ $$K_c = 1.0$$, what is the value of the reaction quotient $$Q$$?

Accepted Answer

$$Q = \dfrac{[C]^3}{[A][B]^2} = \dfrac{(0.30)^3$}{(0.10)(0.20)^2$} = 6.75$$

Question 8

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

Accepted Answer

Adding a catalyst.

Question 9

For the reaction $$2NO_2(g) \rightleftharpoons N_2O_4(g)$$, if the equilibrium constant for the forward reaction is $$K_c = 4.72 at$$ $$100^\circC$$, what is the equilibrium constant for $$N_2O_4(g) \rightleftharpoons 2NO_2(g)$$?

Accepted Answer

$$K_c = 1/4.72$$

Question 10

A closed system initially contains $$1.000 	imes 10$$^{-3}$$\ \mathrm{M}\ H_2$ and 2.000$$ 	imes $$10^{-3}$$\ \mathrm{M}\ $$I_2 at$$ $$448^\circC. At $$equilibrium, $$[HI] = 1.87 	imes 10$$^{-3}$$\ \mathrm{M}. $$What is the equilibrium concentration of $$H_2$$?

Accepted Answer

$$6.5 	imes 10$$^{-5}$$\ \mathrm{M}$$

Question 11

Which of the following is true about heterogeneous equilibria?

Accepted Answer

The concentrations of pure solids and liquids are omitted from the equilibrium constant expression.

Question 12

If the equilibrium constant for a reaction is squared, what has happened to the chemical equation?

Accepted Answer

It has been multiplied by two.

Question 13

For the reaction $$aA + bB \rightleftharpoons dD + eE$$, the equilibrium constant in terms of pressure is:

Accepted Answer

$$K_p = \dfrac{(P_D)^d (P_E)^e}{(P_A)^a (P_B)^b}$$

Question 14

A catalyst is added to a reaction at equilibrium. What is the effect on the equilibrium position and the value of $$K$$?

Accepted Answer

Equilibrium is reached faster, but $$K$$ remains unchanged.

Question 15

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

Accepted Answer

The reaction will shift toward the products.

Question 16

For the reaction $$H_2(g$$) + $$I_2(g$$) \rightleftharpoons 2HI(g)$$, if the initial concentrations are $$[$$H_2$$] = 1.000\ \mathrm{M}$$, $$[$$I_2$$] = 2.000\ \mathrm{M}$$, and K_c = 50.5$ at 448$$^\circ$$C, what is the equilibrium concentration of HI$? (Use the quadratic formula if necessary.)

Accepted Answer

$$[HI] = 2 	imes 0.935 = 1.87\ \mathrm{M}$$

Question 17

Which of the following changes will increase the value of $$K$$ for an endothermic reaction?

Accepted Answer

Increasing the temperature.

Question 18

When two consecutive equilibria are combined, how is the equilibrium constant for the overall reaction determined?

Accepted Answer

By multiplying the equilibrium constants.

Chemical Equilibrium: Principles, Calculations, and Applications

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