Q: Consider the equilibrium $$\mathrm{2NOBr(g) \rightleftharpoons 2NO(g) + Br_2$(g)}$$ with $$K_1 = 0.014$ and $$\mathrm{$$Br_2(g$$) + $$Cl_2(g$$) \rightleftharpoons 2BrCl(g)}$$ with K_2$ = 7.2. $$What is the equilibrium constant $$K_3$$ for the overall reaction $$\mathrm{2NOBr(g) + Cl_2$(g) \rightleftharpoons 2NO(g) + 2BrCl(g)}$$?

$$K_3 = 0.014$$ \times 7.2 = 0.10$$

Q: For the reaction $$\mathrm{N_2$(g) + 3H_2(g) \rightleftharpoons 2NH_3(g)}$$, $$K_c = 613 at$$ $$100^\circC. $$What is the value of $$K_p at $$this temperature? (Assume $$R = 0.0821\ \mathrm{L\cdot atm\cdot $$mol^{-1}$$\cdot K$$^{-1}$$}$$, $$T = 373\ \mathrm{K})$$

$$K_p = K_c(RT$$)^{\Delta n}$$ = 613 \times (0.0821 \times 373$$)^{-2}$$ = 613 \times (30.62$$)^{-2}$$ \approx 0.652$$

Question 1

For the reaction $$\mathrm{N_2O_4(g) \rightleftharpoons 2NO_2(g)}$$, the equilibrium constant $$K_c at a $$certain temperature is 0.212. What is the value of $$K_c$$ for the reaction $$\mathrm{4NO_2(g) \rightleftharpoons 2N_2O_4(g)} at $$the same temperature?

Accepted Answer

$$K_c = (0.212)^2$ = 0.0449$$

Question 2

Consider the equilibrium $$\mathrm{2NOBr(g) \rightleftharpoons 2NO(g) + Br_2$(g)}$$ with $$K_1 = 0.014$ and $$\mathrm{$$Br_2(g$$) + $$Cl_2(g$$) \rightleftharpoons 2BrCl(g)}$$ with K_2$ = 7.2. $$What is the equilibrium constant $$K_3$$ for the overall reaction $$\mathrm{2NOBr(g) + Cl_2$(g) \rightleftharpoons 2NO(g) + 2BrCl(g)}$$?

Accepted Answer

$$K_3 = 0.014$$ 	imes 7.2 = 0.10$$

Question 3

For the reaction $$\mathrm{N_2$(g) + 3H_2(g) \rightleftharpoons 2NH_3(g)}$$, $$K_c = 613 at$$ $$100^\circC. $$What is the value of $$K_p at $$this temperature? (Assume $$R = 0.0821\ \mathrm{L\cdot atm\cdot $$mol^{-1}$$\cdot K$$^{-1}$$}$$, $$T = 373\ \mathrm{K})$$

Accepted Answer

$$K_p = K_c(RT$$)^{\Delta n}$$ = 613 	imes (0.0821 	imes 373$$)^{-2}$$ = 613 	imes (30.62$$)^{-2}$$ \approx 0.652$$

Question 4

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

Accepted Answer

$$K is $$unitless and depends only on temperature for a given reaction.

Question 5

A reaction mixture initially contains $$[A] = 0.50\ \mathrm{M}$$, $$[B] = 0.50\ \mathrm{M}$$, and $$[C] = 0.00\ \mathrm{M}$$ for the reaction $$\mathrm{A + B \rightleftharpoons C}. At $$equilibrium, $$[C] = 0.30\ \mathrm{M}. $$What is the value of $$K_c$$?

Accepted Answer

$$K_c = \frac{[C]}{[A][B]} = \frac{0.30}{(0.20)(0.20)} = 7.5$$

Question 6

For the reaction $$\mathrm{CO(g) + 3H_2(g) \rightleftharpoons CH_4$(g) + H_2O(g)}$$, what will happen if the volume of the reaction vessel is decreased at constant temperature?

Accepted Answer

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

Question 7

A mixture at equilibrium for the reaction $$\mathrm{2SO_2(g) + O_2$(g) \rightleftharpoons 2SO_3(g)}$$ has $$[SO_2$] = 0.10\ \mathrm{M}$$, $$[O_2$] = 0.20\ \mathrm{M}$$, and $$[SO_3$] = 0.40\ \mathrm{M}. If $$more $$SO_2 is $$added, what will happen to the concentrations of $$SO_3$$ and $$O_2 as $$the system returns to equilibrium?

Accepted Answer

$$[SO_3$]$$ will increase and $$[O_2$]$$ will decrease.

Question 8

For the reaction $$\mathrm{$$PbCl_2$$(s) \rightleftharpoons Pb$$^{2+}$$(aq) + 2Cl^-(aq)}$$, which of the following is the correct expression for $$K_c$$?

Accepted Answer

$$K_c = [Pb$$^{2+}$$][Cl^-]^2$$

Question 9

A reaction has $$K_c = 1.2 	imes 10$$^{-5}$$ at 25$$^\circ$$C. Which statement best describes the composition of the equilibrium mixture?

Accepted Answer

The mixture contains mostly reactants and very little product.

Question 10

For the reaction $$\mathrm{H_2$(g) + I_2$(g) \rightleftharpoons 2HI(g)}$$, the initial concentrations are $$[H_2$] = 0.10\ \mathrm{M}$$, $$[I_2$] = 0.10\ \mathrm{M}$$, and $$[HI] = 0.00\ \mathrm{M}. At $$equilibrium, $$[HI] = 0.16\ \mathrm{M}. $$What are the equilibrium concentrations of $$H_2$$ and $$I_2$$?

Accepted Answer

$$[H_2$] = [I_2$] = 0.10 - 0.08 = 0.02\ \mathrm{M}$$

Question 11

For the reaction $$\mathrm{A(g) \rightleftharpoons 2B(g)}$$, the initial concentration of $$A is$$ $$1.00\ \mathrm{M}$$ and $$K_c = 4.0. $$What is the equilibrium concentration of $$A$$? (Assume $$x is $$the amount of $$A$$ that reacts and use the quadratic formula if necessary.)

Accepted Answer

$$[A] = 0.25\ \mathrm{M}$$

Question 12

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

Accepted Answer

Increasing the temperature.

Question 13

A system at equilibrium has $$Q = 5.0$$ and $$K = 2.0. $$What will happen as the system moves toward equilibrium?

Accepted Answer

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

Question 14

For the reaction $$\mathrm{2A(g) + B(g) \rightleftharpoons 3C(g)}$$, how will the equilibrium shift if the total pressure is increased by decreasing the volume?

Accepted Answer

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

Question 15

Which of the following is NOT a correct property of the equilibrium constant $$K$$?

Accepted Answer

$$K is $$affected by the addition of a catalyst.

Question 16

A reaction mixture for $$\mathrm{A(g) \rightleftharpoons 2B(g)}$$ has $$[A] = 0.10\ \mathrm{M}$$ and $$[B] = 0.60\ \mathrm{M}. If$$ $$K_c = 4.0$$, what is the value of $$Q_c$$ and in which direction will the reaction shift to reach equilibrium?

Accepted Answer

$$Q_c = \frac{[B]^2}{[A]} = \frac{(0.60)^2$}{0.10} = 3.6$$; reaction shifts left.

Question 17

For the reaction $$\mathrm{2NO_2(g) \rightleftharpoons N_2O_4(g)}$$, what happens to the equilibrium position and $$K if $$the temperature is decreased, given that the reaction is exothermic?

Accepted Answer

The equilibrium shifts right and $$K$$ decreases.

Question 18

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

Accepted Answer

The forward and reverse reaction rates are equal, and concentrations of all species remain constant.

Question 19

A student dissolves $$PbCl_2(s$$)$$ in water and finds $$[$$Pb^{2+}$$] = 1.0 	imes $$10^{-3}$$\ \mathrm{M}$$ and $$[Cl^-] = 2.0 	imes $$10^{-3}$$\ \mathrm{M}$$ at equilibrium. What is the value of K_c$ for this dissolution?

Accepted Answer

$$K_c = [Pb$$^{2+}$$][Cl^-]^2 = (1.0 	imes 10$$^{-3}$$)(2.0 	imes 10$$^{-3}$$)^2 = 4.0$$ 	imes $$10^{-9}$

Chemical Equilibrium: Principles, Calculations, and Le Châtelier’s Principle

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