Q: For the reaction $PCl_3(g) + Cl_2(g) \rightleftharpoons PCl_5(g)$, $K = 24$ at a certain temperature. If at a given moment $[PCl_3] = 0.22$ M, $[Cl_2] = 0.1046$ M, and $[PCl_5] = 0.30$ M, what is the value of $Q$ and which direction will the reaction shift to reach equilibrium?

$Q = \frac{0.30}{0.22 \times 0.1046} = 13.0$, so the reaction will shift to the right.

Question 1

Which of the following best describes a system at dynamic equilibrium?

Accepted Answer

The rates of the forward and reverse reactions are equal, but the concentrations of reactants and products are not necessarily equal.

Question 2

For the reaction $\mathrm{O_2(g) + NO(g) \rightarrow NO_3(g)}$, what is the correct equilibrium constant expression?

Accepted Answer

$K = \frac{[NO_3]}{[O_2][NO]}$

Question 3

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

Accepted Answer

A large $K$ (e.g., $K = 1000$) means the reaction favors products at equilibrium.

Question 4

Given the reaction $2 NO_2(g) \rightarrow N_2(g) + 2 O_2(g)$, what is the correct equilibrium constant expression?

Accepted Answer

$K = \frac{[N_2][O_2]^2}{[NO_2]^2}$

Question 5

For the reaction $2 Al(s) + 3 O_2(g) \rightarrow 2 Al_2O_3(s)$, what is the correct equilibrium constant expression?

Accepted Answer

$K = \frac{1}{[O_2]^3}$

Question 6

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

Accepted Answer

The reaction mixture at equilibrium contains mostly reactants.

Question 7

If the equation for a reaction is reversed, how does the new equilibrium constant $K'$, relate to the original $K$?

Accepted Answer

$K' = \frac{1}{K}$

Question 8

For the reaction $PCl_3(g) + Cl_2(g) \rightleftharpoons PCl_5(g)$, $K = 24$ at a certain temperature. If at a given moment $[PCl_3] = 0.22$ M, $[Cl_2] = 0.1046$ M, and $[PCl_5] = 0.30$ M, what is the value of $Q$ and which direction will the reaction shift to reach equilibrium?

Accepted Answer

$Q = \frac{0.30}{0.22 	imes 0.1046} = 13.0$, so the reaction will shift to the right.

Question 9

Which of the following changes will cause the equilibrium to shift to the right for the reaction $N_2(g) + 3 H_2(g) \rightleftharpoons 2 NH_3(g)$?

Accepted Answer

Removing $NH_3(g)$ from the system.

Question 10

For the reaction $CaO(s) + CO_2(g) \rightleftharpoons CaCO_3(s)$, which of the following will shift the equilibrium to the left?

Accepted Answer

Decreasing the pressure of $CO_2(g)$.

Question 11

If the equilibrium constant $K$ for a reaction is 0.20, what is the value of $K$ for the reaction if the equation is multiplied by 2?

Accepted Answer

$K = 0.20^2 = 0.040$

Question 12

For the reaction $3 H_2(g) + N_2(g) \rightleftharpoons 2 NH_3(l)$, which of the following is true about the equilibrium constant expression?

Accepted Answer

The concentration of $NH_3(l)$ does not appear in the equilibrium constant expression.

Question 13

Which of the following best explains why solids and liquids are not included in equilibrium constant expressions?

Accepted Answer

Their concentrations do not change during the reaction.

Question 14

For the reaction $HBr(l) \rightarrow H_2(g) + Br_2(g)$, what is the correct equilibrium constant expression?

Accepted Answer

$K = [H_2][Br_2]$

Question 15

If a system at equilibrium is disturbed by adding more reactant, according to Le Chatelier’s Principle, what will happen?

Accepted Answer

The system will shift to the right to form more products.

Question 16

For the reaction $PCl_3(g) + Cl_2(g) \rightleftharpoons PCl_5(g)$ at equilibrium, what will happen if $PCl_5(g)$ is removed from the system?

Accepted Answer

The reaction will shift to the right to produce more $PCl_5(g)$.

Question 17

Which of the following is true at equilibrium?

Accepted Answer

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

Question 18

For a gaseous reaction, the relationship between $K_p$ and $K_c$ is given by $K_p = K_c(RT)^{\Delta n}$. If $\Delta n = 2$, $K_c = 0.5$, $R = 0.08206$, and $T = 300$ K, what is $K_p$?

Accepted Answer

$K_p = 0.5 	imes (0.08206 	imes 300)^2 = 30.2$

Chemical Equilibrium: Principles, Constants, and Applications

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