Question 1

Which of the following statements best describes a chemical equilibrium?

Accepted Answer

It is a dynamic state where the rates of the forward and reverse reactions are equal, and concentrations remain constant.

Question 2

For the reaction $\mathrm{N_2(g) + 3H_2(g) \rightleftharpoons 2NH_3(g)}$, which is the correct equilibrium constant expression $K_c$?

Accepted Answer

$K_c = \dfrac{[NH_3]^2}{[N_2][H_2]^3}$

Question 3

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

Accepted Answer

The mixture contains mostly products.

Question 4

Consider the reaction $\mathrm{N_2O_4(g) \rightleftharpoons 2NO_2(g)}$. If the partial pressure of $\mathrm{N_2O_4}$ is 0.0145 atm and $\mathrm{NO_2}$ is 0.0761 atm at equilibrium, what is the value of $K_p$?

Accepted Answer

$K_p = \dfrac{(0.0761)^2}{0.0145}$

Question 5

Which of the following will NOT appear in the equilibrium constant expression for the reaction $\mathrm{H_2O(l) + C(s) \rightleftharpoons H_2(g) + CO(g)}$?

Accepted Answer

$[H_2O]$

Question 6

For the reaction $\mathrm{2A \rightleftharpoons B}$, the equilibrium constant is $K$. What is the equilibrium constant for the reverse reaction $\mathrm{B \rightleftharpoons 2A}$?

Accepted Answer

$\dfrac{1}{K}$

Question 7

If the coefficients in a balanced chemical equation are doubled, how does this affect the equilibrium constant $K$?

Accepted Answer

The new $K$ is the original $K$ squared.

Question 8

Given the reaction $\mathrm{N_2(g) + 3H_2(g) \rightleftharpoons 2NH_3(g)}$, what will happen if more $\mathrm{N_2}$ is added to a system at equilibrium?

Accepted Answer

The reaction will shift toward the products.

Question 9

For the reaction $\mathrm{N_2(g) + 3H_2(g) \rightleftharpoons 2NH_3(g)}$, what effect will increasing the pressure have on the position of equilibrium?

Accepted Answer

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

Question 10

Which of the following best describes Le Châtelier's Principle?

Accepted Answer

If a system at equilibrium is disturbed, the system will shift to minimize the disturbance and restore equilibrium.

Question 11

A reaction mixture at equilibrium contains $[A] = 0.50\ \mathrm{M}$, $[B] = 0.25\ \mathrm{M}$, and $[C] = 0.10\ \mathrm{M}$ for the reaction $\mathrm{A + 2B \rightleftharpoons C}$. What is the value of $K_c$?

Accepted Answer

$K_c = \dfrac{[C]}{[A][B]^2}$

Question 12

For the reaction $\mathrm{2NO_2(g) \rightleftharpoons N_2O_4(g)}$, if $K_c = 0.212$ for the forward reaction, what is $K_c$ for the reverse reaction?

Accepted Answer

$K_c = \dfrac{1}{0.212}$

Question 13

Which of the following changes will increase the yield of ammonia in the Haber process ($\mathrm{N_2(g) + 3H_2(g) \rightleftharpoons 2NH_3(g)}$), assuming the reaction is exothermic?

Accepted Answer

Removing $\mathrm{NH_3}$ as it forms.

Question 14

A closed system contains only products at the start of a reversible reaction. What will happen as the system approaches equilibrium?

Accepted Answer

Reactants will begin to form until equilibrium is reached.

Question 15

For the reaction $\mathrm{H_2CO_3(aq) + NaOH(aq) \rightleftharpoons H_2O(l) + NaHCO_3(aq)}$, which species should NOT be included in the equilibrium constant expression?

Accepted Answer

$[H_2O]$

Question 16

If $K_c$ for a reaction is 1.5 and the initial concentrations are $[A] = 1.0\ \mathrm{M}$, $[B] = 1.0\ \mathrm{M}$, and $[C] = 0.5\ \mathrm{M}$ for $\mathrm{A + B \rightleftharpoons C}$, which direction will the reaction shift to reach equilibrium?

Accepted Answer

Toward the products.

Question 17

Which of the following is true about the equilibrium constant $K$?

Accepted Answer

It is only affected by temperature.

Question 18

A reaction has $\Delta n = 2$ (where $\Delta n$ is moles of gaseous products minus moles of gaseous reactants). If $K_c = 0.212$ at 100°C, what is the formula to calculate $K_p$?

Accepted Answer

$K_p = K_c(RT)^{2}$

Chemical Equilibria: Principles, Calculations, and Applications

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