Q: In a closed system at equilibrium, what happens if some $CO_2(g)$ is removed from the reaction $\mathrm{CaCO_3(s) \rightleftharpoons CaO(s) + CO_2(g)}$?

More $CaCO_3$ will decompose to restore equilibrium.

Q: Which of the following is a correct equilibrium constant expression for the reaction $\mathrm{NH_3(aq) + H_2O(l) \rightleftharpoons NH_4^+(aq) + OH^-(aq)}$?

$K_c = \frac{[NH_4^+][OH^-]}{[NH_3]}$

Q: A student sets up a reaction with only $CaO(s)$ and $CO_2(g)$ at a pressure greater than $K_p$ for the reaction $\mathrm{CaCO_3(s) \rightleftharpoons CaO(s) + CO_2(g)}$. What will happen as the system moves toward equilibrium?

$CO_2$ will react with $CaO$ to form $CaCO_3$ until equilibrium is reached.

Q: Which of the following best describes the role of a sacrificial reductant in a photoredox catalytic cycle?

It donates electrons to regenerate the photocatalyst.

Q: In the context of photoredox chemistry, what does 'metal-to-ligand charge transfer' (MLCT) refer to?

An electron moves from a metal orbital to a ligand orbital upon photoexcitation.

Q: Which of the following is true about the equilibrium of a system containing $Br_2(l)$ and $Br_2(g)$ in a closed container?

The equilibrium constant depends only on the vapor pressure of $Br_2(g)$.

Question 1

Which of the following best explains why equilibrium constants ($K_c$ and $K_p$) are unitless?

Accepted Answer

Because the concentrations and pressures used are actually dimensionless activities.

Question 2

For the reaction $\mathrm{CaCO_3(s) \rightleftharpoons CaO(s) + CO_2(g)}$, which of the following is true about the equilibrium constant expression?

Accepted Answer

$K_p = P_{CO_2}$

Question 3

A reaction vessel contains $\mathrm{Br_2(g) + Cl_2(g) \rightleftharpoons 2BrCl(g)}$ with an initial partial pressure of 1.00 atm BrCl and $K_p = 7.0$ at 400 K. What is the equilibrium partial pressure of BrCl?

Accepted Answer

0.57 atm

Question 4

Why are pure solids and liquids omitted from equilibrium constant expressions?

Accepted Answer

Their activities are 1 and their concentrations do not change during the reaction.

Question 5

Given the reaction $\mathrm{CH_4(g) + I_2(g) ightleftharpoons CH_3I(g) + HI(g)}$ with $K_p = 2.26 	imes 10^{-4}$ at 630 K, and initial partial pressures $P_{CH_4} = 0.138$ atm and $P_{I_2} = 0.105$ atm, what is the equilibrium partial pressure of HI?

Accepted Answer

0.00178 atm

Question 6

Which of the following statements about heterogeneous equilibria is correct?

Accepted Answer

The amount of solid present does not affect the equilibrium position as long as some is present.

Question 7

For the reaction $\mathrm{2NO(g) + 2H_2(g) \rightleftharpoons N_2(g) + 2H_2O(g)}$, if the equilibrium concentrations are $[NO] = 0.062$ M, $[H_2] = 0.012$ M, $[N_2] = 0.019$ M, and $[H_2O] = 0.138$ M, what is the value of $K_c$?

Accepted Answer

$K_c = 654$

Question 8

Which shortcut can be used when solving for equilibrium concentrations if $x$ is much smaller than the initial concentrations?

Accepted Answer

Neglect $x$ in the denominator if $x < 5\%$ of the initial value.

Question 9

In a closed system at equilibrium, what happens if some $CO_2(g)$ is removed from the reaction $\mathrm{CaCO_3(s) \rightleftharpoons CaO(s) + CO_2(g)}$?

Accepted Answer

More $CaCO_3$ will decompose to restore equilibrium.

Question 10

Which of the following is a correct equilibrium constant expression for the reaction $\mathrm{NH_3(aq) + H_2O(l) \rightleftharpoons NH_4^+(aq) + OH^-(aq)}$?

Accepted Answer

$K_c = \frac{[NH_4^+][OH^-]}{[NH_3]}$

Question 11

A student sets up a reaction with only $CaO(s)$ and $CO_2(g)$ at a pressure greater than $K_p$ for the reaction $\mathrm{CaCO_3(s) \rightleftharpoons CaO(s) + CO_2(g)}$. What will happen as the system moves toward equilibrium?

Accepted Answer

$CO_2$ will react with $CaO$ to form $CaCO_3$ until equilibrium is reached.

Question 12

Which of the following best describes the role of a sacrificial reductant in a photoredox catalytic cycle?

Accepted Answer

It donates electrons to regenerate the photocatalyst.

Question 13

In the context of photoredox chemistry, what does 'metal-to-ligand charge transfer' (MLCT) refer to?

Accepted Answer

An electron moves from a metal orbital to a ligand orbital upon photoexcitation.

Question 14

Which of the following is true about the equilibrium of a system containing $Br_2(l)$ and $Br_2(g)$ in a closed container?

Accepted Answer

The equilibrium constant depends only on the vapor pressure of $Br_2(g)$.

Question 15

A reaction mixture initially contains 0.100 mol NO, 0.050 mol H2, and 0.100 mol H2O in a 1.00 L vessel. At equilibrium, [NO] = 0.062 M. What is the equilibrium concentration of H2?

Accepted Answer

0.012 M

Question 16

For the reaction $\mathrm{Br_2(g) + Cl_2(g) \rightleftharpoons 2BrCl(g)}$, if the initial partial pressures of Br2 and Cl2 are both zero and BrCl is 1.00 atm, what is the correct setup for the ICE table?

Accepted Answer

Br2: 0 + x; Cl2: 0 + x; BrCl: 1.00 - 2x

Question 17

Which of the following is a correct statement about solvents in equilibrium constant expressions?

Accepted Answer

If a reactant or product is also the solvent, it is omitted from the equilibrium expression.

Equilibrium Constants and Heterogeneous Equilibria: General Chemistry Study Guide

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