Q: For the reaction $2 SO_2 (g) + O_2 (g) \rightleftharpoons 2 SO_3 (g)$, initially 0.30 M SO$_2$ and 0.20 M O$_2$ are mixed. At equilibrium, [SO$_3$] = 0.0150 M. What is the value of $K_c$?

$K_c = \frac{(0.0150)^2}{(0.30 - 2 \times 0.0150)^2 (0.20 - 0.0150)}$

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 is the correct equilibrium constant expression?

Accepted Answer

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

Question 3

For the reaction $2 SO_2 (g) + O_2 (g) \rightleftharpoons 2 SO_3 (g)$, if the equilibrium constant $K$ is multiplied by 3, what happens to the value of $K$?

Accepted Answer

It is cubed: $K_{new} = K^3$

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 $K_p = K_c (RT)^{\Delta n}$, for which reaction will $K_p = K_c$?

Accepted Answer

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

Question 7

A reaction has $K = 1.2 	imes 10^5$ at a certain temperature. Which statement is true?

Accepted Answer

The reaction favors products at equilibrium.

Question 8

For the reaction $2 NOBr (g) \rightleftharpoons 2 NO (g) + Br_2 (g)$, if $K = 0.75$ and the initial concentrations are $[NOBr] = 1.25$ M, $[NO] = 0.80$ M, $[Br_2] = 0.50$ M, what will happen?

Accepted Answer

The partial pressure of NOBr will increase.

Question 9

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

Accepted Answer

Removing $O_2$

Question 10

If the rate constant for the forward reaction is $k_{forward} = 2.0 	imes 10^{-2}$ and for the reverse reaction is $k_{reverse} = 4.0 	imes 10^{-5}$, what is the equilibrium constant $K$?

Accepted Answer

$K = 5.0 	imes 10^{2}$

Question 11

For the reaction $2 NO (g) + Br_2 (g) \rightleftharpoons 2 NOBr (g)$, if $K = 10$ and the reaction quotient $Q = 30$, what will happen?

Accepted Answer

The reaction will shift to the left to form more reactants.

Question 12

Which of the following is NOT included in the equilibrium constant expression?

Accepted Answer

Solids

Question 13

For the reaction $PCl_5 (g) \rightleftharpoons PCl_3 (g) + Cl_2 (g)$, which is true about $K_p$ and $K_c$?

Accepted Answer

$K_p < K_c$

Question 14

A reaction mixture initially contains 0.15 atm COBr$_2$. At equilibrium, the partial pressure of CO is found to be 0.10 atm. If $K_p = 4.08$ for $COBr_2 (g) \rightleftharpoons CO (g) + Br_2 (g)$, what is the equilibrium partial pressure of Br$_2$?

Accepted Answer

0.10 atm

Question 15

Which of the following will increase the yield of products for the exothermic reaction $N_2 (g) + 3 H_2 (g) \rightleftharpoons 2 NH_3 (g) + heat$?

Accepted Answer

Decreasing the temperature

Question 16

If the equilibrium constant for a reaction increases with increasing temperature, the reaction is:

Accepted Answer

Endothermic

Question 17

For the reaction $2 SO_2 (g) + O_2 (g) \rightleftharpoons 2 SO_3 (g)$, initially 0.30 M SO$_2$ and 0.20 M O$_2$ are mixed. At equilibrium, [SO$_3$] = 0.0150 M. What is the value of $K_c$?

Accepted Answer

$K_c = \frac{(0.0150)^2}{(0.30 - 2 	imes 0.0150)^2 (0.20 - 0.0150)}$

Chemical Equilibrium: Concepts, Calculations, and Applications

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