Q: For the reaction $$2 NOBr (g) \rightleftharpoons 2 NO (g) + Br_2$ (g)$$, if $$[NOBr] = 0.50 M$$, $$[NO] = 0.20 M$$, and $$[Br_2$] = 0.10 M at $$equilibrium, what is the value of $$K_c$$?

$$K_c = \frac{[NO]^2 [Br_2$]}{[NOBr]^2} = \frac{(0.20)^2$ \times 0.10}{(0.50)^2$} = 0.016$$

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, and concentrations remain constant.

Question 2

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

Accepted Answer

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

Question 3

For the reaction $$2 NO_2$ (g) \rightleftharpoons 2 NO (g) + O_2$ (g)$$, if $$K_p is $$known, which formula relates $$K_p$$ and $$K_c$$?

Accepted Answer

$$K_p = K_c (RT$$)^{\Delta n}$$

Question 4

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

Accepted Answer

Adding a catalyst

Question 5

For the reaction $$N_2 (g) + 3$$ $$H_2 (g$$) \rightleftharpoons 2 $$NH_3 (g$$)$$, what is the value of $$\Delta n$$ when relating K_p$ and K_c$?

Accepted Answer

$$\Delta n = 2 - 4 = -2$$

Question 6

If the equilibrium constant $$K$$ for a reaction is much greater than 1, which of the following is true?

Accepted Answer

The reaction favors the formation of products.

Question 7

A reaction mixture initially contains 0.10 M H$$_2$$ and 0.10 M I$$_2$$ with no HI. At equilibrium, the concentration of HI is found to be 0.12 M. What is the equilibrium constant expression for this reaction: $$H_2 (g$$) + $$I_2 (g$$) \rightleftharpoons 2 HI (g)$$?

Accepted Answer

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

Question 8

Which of the following scenarios will shift the equilibrium to the right for the endothermic reaction $$N_2O_4 (g) \rightleftharpoons 2 NO_2$ (g)$$?

Accepted Answer

Adding more $$N_2O_4$$

Question 9

If the rate constant for the forward reaction is $$k_{forward} = 2.0 	imes 10$$^{-3}$$ and for the reverse reaction is k$$_{reverse} = 4.0 	imes $$10^{-5}$$, what is the equilibrium constant $$K$$?

Accepted Answer

$$K = 5.0 	imes 10$$^{1}$$

Question 10

For the reaction $$2 SO_2$ (g) + O_2$ (g) \rightleftharpoons 2 SO_3$ (g)$$, if the equilibrium constant $$K_c is 10 at 700 K$$, what will be the new equilibrium constant if the reaction is reversed?

Accepted Answer

$$K_{new} = 0.1$$

Question 11

Which of the following best describes the effect of increasing temperature on an exothermic reaction at equilibrium?

Accepted Answer

The equilibrium shifts to the left, favoring reactants.

Question 12

A reaction has $$K_c = 1.2 	imes 10$$^{-5}$$ at 25°C. If the reaction quotient Q$ is 2.5$$ 	imes $$10^{-6}$$, what will happen as the system moves toward equilibrium?

Accepted Answer

The reaction will shift to the right, forming more products.

Question 13

Which of the following is NOT a valid shortcut for solving ICE chart equilibrium problems?

Accepted Answer

Ignoring the change in concentration for all species regardless of $$K$$ value.

Question 14

For the reaction $$2 NOBr (g) \rightleftharpoons 2 NO (g) + Br_2$ (g)$$, if $$[NOBr] = 0.50 M$$, $$[NO] = 0.20 M$$, and $$[Br_2$] = 0.10 M at $$equilibrium, what is the value of $$K_c$$?

Accepted Answer

$$K_c = \frac{[NO]^2 [Br_2$]}{[NOBr]^2} = \frac{(0.20)^2$ 	imes 0.10}{(0.50)^2$} = 0.016$$

Question 15

Which of the following disturbances will shift the equilibrium to the left for the reaction $$2 SO_2$ (g) + O_2$ (g) \rightleftharpoons 2 SO_3$ (g)$$?

Accepted Answer

Removing $$SO_2$$

Question 16

If the equilibrium constant for a reaction is $$K = 1.0 	imes 10$$^{-8}$$, which statement is most accurate?

Accepted Answer

The reaction strongly favors reactants at equilibrium.

Question 17

For the reaction $$2 SO_2$ (g) + O_2$ (g) \rightleftharpoons 2 SO_3$ (g)$$, if the equilibrium constant for the forward reaction is $$K$$, what is the equilibrium constant for the reaction $$SO_3 (g$$) \rightleftharpoons $$SO_2 (g) + 0.5$$ $$O_2 (g$$)$$?

Accepted Answer

$$1/K^{1/2}$$

Chemical Equilibrium: Concepts, Calculations, and Applications

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