Q: For the reaction $$2 SO_2$ (g) + O_2$ (g) \rightleftharpoons 2 SO_3$ (g)$$, initially $$[SO_2$] = 0.30 M$$, $$[O_2$] = 0.20 M$$, and $$[SO_3$] = 0. At $$equilibrium, $$[SO_3$] = 0.015 M. $$What is the value of $$K_c$$?

$$K_c = \frac{(0.015)^2$}{(0.30 - 2 \times 0.015)^2$ (0.20 - 0.015)}$$

Q: For the reaction $$2 NO (g) + Br_2$ (g) \rightleftharpoons 2 NOBr (g)$$, $$K_p = 2.5 \times 10^2$ at 35ºC. If $$[NO] = 0.2$$ atm and $$[$$Br_2$$] = 0.050$$ atm at equilibrium, what is the equilibrium concentration of $$NOBr$$?

$$[NOBr] = \sqrt{K_p \times [NO]^2 \times [Br_2$]}$$

Question 1

Which of the following best describes what happens at chemical equilibrium for a reversible reaction?

Accepted Answer

The rate of the forward reaction equals the rate of the reverse reaction.

Question 2

Given the reaction: $$aA + bB \rightleftharpoons cC + dD$$, which is the correct equilibrium constant expression?

Accepted Answer

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

Question 3

For the reaction $$2 NO_2$ (g) \rightleftharpoons 2 NO (g) + O_2$ (g)$$, which of the following would increase the amount of $$NO_2 at $$equilibrium?

Accepted Answer

Adding more $$NO$$ gas.

Question 4

Which of the following is NOT included in the equilibrium constant expression for the reaction $$CaCO_3 (s$$) \rightleftharpoons CaO (s) + $$CO_2 (g$$)$$?

Accepted Answer

$$[$$CaCO_3$$]$$

Question 5

If $$K_c$$ for a reaction is much greater than 1, what does this indicate about the position of equilibrium?

Accepted Answer

Products are favored.

Question 6

For the reaction $$N_2 (g) + 3$$ $$H_2 (g$$) \rightleftharpoons 2 $$NH_3 (g$$)$$, K_p$ and K_c$ are related by K_p = K_c$$ $$(RT)^{\Delta n}. $$What is the value of $$\Delta n$$ for this reaction?

Accepted Answer

$$\Delta n = 2 - (1+3) = -2$$

Question 7

A reaction has $$K_c = 1.2 	imes 10$$^{-5}$$ at 300 K. If the reaction is reversed, what is the new equilibrium constant?

Accepted Answer

$$K_c' = 8.3 	imes 10^4$

Question 8

Which of the following changes will NOT affect the position of equilibrium for a reaction at constant temperature?

Accepted Answer

Adding a catalyst.

Question 9

For the reaction $$2 SO_2$ (g) + O_2$ (g) \rightleftharpoons 2 SO_3$ (g)$$, initially $$[SO_2$] = 0.30 M$$, $$[O_2$] = 0.20 M$$, and $$[SO_3$] = 0. At $$equilibrium, $$[SO_3$] = 0.015 M. $$What is the value of $$K_c$$?

Accepted Answer

$$K_c = \frac{(0.015)^2$}{(0.30 - 2 	imes 0.015)^2$ (0.20 - 0.015)}$$

Question 10

A mixture of $$N_2$$, $$H_2$$, and $$NH_3 is $$placed in a container. At a certain time, $$[N_2$] = 0.650 M$$, $$[H_2$] = 0.330 M$$, and $$[NH_3$] = 0.529 M. $$What is the reaction quotient $$Q$$ for $$N_2 (g) + 3$$ $$H_2 (g$$) \rightleftharpoons 2 $$NH_3 (g$$)$$?

Accepted Answer

$$Q = \frac{[NH_3$]^2}{[N_2$][H_2$]^3}$$

Question 11

For the reaction $$2 NOBr (g) \rightleftharpoons 2 NO (g) + Br_2$ (g)$$, $$K_c = 0.75 at 750 K. If$$ $$[NOBr] = 1.25 M$$, $$[NO] = 0.80 M$$, and $$[Br_2$] = 0.50 M$$, what will happen as the system moves toward equilibrium?

Accepted Answer

The partial pressure of NOBr will increase.

Question 12

Which of the following disturbances will shift the equilibrium of the endothermic reaction $$6 CO_2$ (g) + 6 H_2O (g) \rightleftharpoons C_6H_{12}O_6$ (s) + 6 O_2$ (g) to $$the right?

Accepted Answer

Removing $$O_2$$ gas.

Question 13

If the equilibrium constant $$K_p$$ for a reaction increases with increasing temperature, what can you conclude about the reaction?

Accepted Answer

The reaction is endothermic.

Question 14

For the reaction $$PCl_5 (g$$) \rightleftharpoons $$PCl_3 (g$$) + $$Cl_2 (g$$)$$, which of the following is true?

Accepted Answer

$$K_p \u003c K_c$$

Question 15

Which of the following is a correct statement about the effect of a catalyst on a system at equilibrium?

Accepted Answer

A catalyst increases the rate at which equilibrium is achieved.

Question 16

For the reaction $$2 NO (g) + Br_2$ (g) ightleftharpoons 2 NOBr (g)$$, $$K_p = 2.5 	imes 10^2$ at 35ºC. If $$[NO] = 0.2$$ atm and $$[$$Br_2$$] = 0.050$$ atm at equilibrium, what is the equilibrium concentration of $$NOBr$$?

Accepted Answer

$$[NOBr] = \sqrt{K_p 	imes [NO]^2 	imes [Br_2$]}$$

Question 17

Which of the following reactions will have $$K_p = K_c$$?

Accepted Answer

$$N_2 (g$$) + $$O_2 (g$$) \rightleftharpoons 2 NO (g)$$

Principles of Chemical Equilibrium – Study Notes

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