Question 1

Which statement best describes chemical equilibrium in a reversible reaction?

Accepted Answer

The rate of the forward reaction is equal to the rate of the reverse reaction.

Question 2

For the reaction $$\mathrm{N_2$(g) + 3H_2(g) \rightleftharpoons 2NH_3(g)}$$, if $$K_c = 1.2$$ and $$Q_c = 0.611$$, what direction will the reaction proceed to reach equilibrium?

Accepted Answer

The reaction will proceed from reactants to products.

Question 3

Given the equilibrium $$\mathrm{$$COF_2$$ \rightleftharpoons CO_2$ + CF_4$}$$, with $$[$$COF_2$$] = 0.255\,M$$, $$[CF_4$] = 0.118\,M$$, and $$K_c = 2.00$$, what is the equilibrium concentration of $$CO_2$$?

Accepted Answer

$$[CO_2$] = 1.10\,M$$

Question 4

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

Accepted Answer

Products are favored at equilibrium.

Question 5

For the reaction $$\mathrm{aA + bB \rightleftharpoons cC + dD}$$, how is the reaction quotient $$Q_c$$ calculated?

Accepted Answer

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

Question 6

A mixture initially contains $$[NO_2$] = 0.100\,M$$ and $$[N_2O_4] = 0.00\,M. If$$ $$K_c = 0.36$$, what is the value of $$Q_c$$ and what direction will the reaction proceed?

Accepted Answer

$$Q_c = \infty$$, reaction proceeds left

Question 7

For the equilibrium $$\mathrm{2A(g) ightleftharpoons B(g) + C(g)}$$ with $$K_c = 2.5 	imes 10$$^{-7}$$ and 1.6 moles of A in a 4 L vessel, what is the initial concentration of A?

Accepted Answer

$$0.4\,M$$

Question 8

In the reaction $$\mathrm{2NO(g) \rightleftharpoons N_2$(g) + O_2$(g)}$$ with $$K_c = 83.3$$, 3 moles of NO are placed in a 2 L container. What is the equilibrium concentration of NO if $$x = 1.42$$?

Accepted Answer

$$0.078\,M$$

Question 9

For the reaction $$\mathrm{2NO(g) \rightleftharpoons N_2$(g) + O_2$(g)}$$, what is the concentration of O$$_2$$ formed at equilibrium if $$x = 1.42$$?

Accepted Answer

$$0.711\,M$$

Question 10

For the equilibrium $$\mathrm{2H_2S(g) ightleftharpoons 2H_2(g) + S_2$(g)} at$$ $$800^\circ C$$ with $$K_c = 1.67 	imes 10$$^{-7}$$ and initial $$[H_2S] = 0.0250\,M$$, what is the equilibrium concentration of S_2$ if x = 2.97$$ 	imes $$10^{-4}$$?

Accepted Answer

$$2.97 	imes 10$$^{-4}$$\,M$$

Question 11

If $$Q_c \u003e K_c$$ for a reaction, what does this indicate about the direction the reaction will proceed?

Accepted Answer

The reaction will proceed from products to reactants.

Question 12

For the equilibrium $$\mathrm{H_2$(g) + I_2$(g) \rightleftharpoons 2HI(g)}$$ with $$K_c = 60$$ and 2 moles each of $$H_2$$ and $$I_2 in a 3 L $$flask, what is the equilibrium concentration of $$HI if$$ $$x = 1.59$$?

Accepted Answer

$$1.059\,M$$

Question 13

In an ICE table for the reaction $$\mathrm{2NO_2 \rightleftharpoons N_2O_4}$$, if the initial concentration of $$NO_2 is$$ $$0.100\,M$$ and $$N_2O_4 is$$ $$0.00\,M$$, what is the change in concentration for $$NO_2$$?

Accepted Answer

$$-2x$$

Question 14

For the equilibrium $$\mathrm{X_2$(g) + Y_2$(g) \rightleftharpoons 2XY(g)}$$ with $$K_c = 49$$ and 1 mol each of $$X_2$$ and $$Y_2 in a 3 L $$flask, what is the initial concentration of $$X_2$$?

Accepted Answer

$$0.33\,M$$

Question 15

If the equilibrium constant $$K_c$$ for a reaction is much less than 1, what does this imply about the equilibrium mixture?

Accepted Answer

The mixture contains mostly reactants.

Question 16

For the equilibrium $$\mathrm{2NO_2 \rightleftharpoons N_2O_4}$$, if $$K_c = 0.36$$ and equilibrium concentrations are $$[NO_2$] = 0.072\,M$$ and $$[N_2O_4] = 0.014\,M$$, what is the value of $$K_c$$ calculated from these concentrations?

Accepted Answer

$$0.37$$

Question 17

In solving equilibrium problems, why is the quadratic formula sometimes necessary?

Accepted Answer

Because equilibrium expressions often result in quadratic equations.

Question 18

For the reaction $$\mathrm{Br_2$(g) ightleftharpoons 2Br(g)}$$ with $$K_c = 1.1 	imes 10$$^{-3}$$, initial $$[$$Br_2$$] = 0.063\,M$$ and $$[Br] = 0.012\,M$$, what is the equilibrium concentration of Br$ if x = -0.00178$?

Accepted Answer

$$0.00844\,M$$

Chemical Equilibrium: Calculating Equilibrium Concentrations

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