CHEM134 Practice Exam 8 Chemical
Equilibrium Practice Exam Questions
And Correct Answers (Verified
Answers) Plus Rationales 2026 Q&A |
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1. Which statement best describes a chemical system at equilibrium?
A. The concentrations of reactants and products are equal.
B. The reaction has completely stopped.
C. The forward and reverse reactions occur at equal rates.
D. All reactants have been converted into products.
Answer: C. The forward and reverse reactions occur at equal rates.
Rationale: At dynamic equilibrium, the forward and reverse reactions
continue simultaneously, but they occur at the same rate. Because the
rates are equal, the macroscopic concentrations of reactants and
products remain constant. Equilibrium does not require equal
concentrations, nor does it mean that the reaction has stopped.
2. For the reaction N₂(g) + 3H₂(g) ⇌ 2NH₃(g), which expression
correctly represents Kc?
A. Kc = [NH₃]²/[N₂][H₂]³
B. Kc = [N₂][H₂]³/[NH₃]²
C. Kc = [NH₃]/[N₂][H₂]
D. Kc = [NH₃]²/[N₂][H₂]
Answer: A. Kc = [NH₃]²/[N₂][H₂]³
,Rationale: The equilibrium constant expression places the equilibrium
concentrations of products in the numerator and reactants in the
denominator. Each concentration is raised to the power of its
stoichiometric coefficient. Therefore, NH₃ is squared, H₂ is cubed, and
N₂ has an exponent of one.
3. What does a large value of K generally indicate for a reaction at
equilibrium?
A. The reaction is necessarily fast.
B. The equilibrium mixture contains relatively more products than
reactants.
C. The reaction has a large activation energy.
D. The reaction must be exothermic.
Answer: B. The equilibrium mixture contains relatively more
products than reactants.
Rationale: A large equilibrium constant indicates that products are
favored thermodynamically at equilibrium. It does not indicate
reaction speed, activation energy, or whether the reaction is
exothermic. A reaction can have a large K and still proceed slowly.
4. For the reaction 2SO₂(g) + O₂(g) ⇌ 2SO₃(g), what happens to the
equilibrium position when additional SO₂ is added?
A. It shifts toward reactants.
B. It remains unchanged.
C. The equilibrium constant decreases.
D. It shifts toward products.
Answer: D. It shifts toward products.
Rationale: Adding SO₂ increases the concentration of a reactant.
According to Le Châtelier’s principle, the system responds by
,consuming some of the added SO₂, shifting toward the products. At
constant temperature, the equilibrium constant itself does not change.
5. Which factor changes the numerical value of an equilibrium
constant?
A. Adding a catalyst
B. Changing the initial concentrations
C. Changing the temperature
D. Changing the amount of a pure solid
Answer: C. Changing the temperature
Rationale: Temperature is the only factor among the choices that
changes the value of K. Concentration changes can shift the
equilibrium position, but K remains constant at a fixed temperature.
Catalysts affect the rates of both forward and reverse reactions and
therefore do not change K. Pure solids are not included in the
equilibrium expression.
6. For a reaction at equilibrium, Q is calculated using the same
mathematical form as K. If Q < K, what occurs?
A. The reaction shifts toward products.
B. The reaction shifts toward reactants.
C. The reaction is already at equilibrium.
D. The reaction becomes impossible.
Answer: A. The reaction shifts toward products.
Rationale: Q compares the current composition of the system with the
equilibrium composition. If Q is smaller than K, there are relatively
too few products compared with the equilibrium condition. The
reaction therefore proceeds in the forward direction until Q reaches K.
, 7. Which substances are omitted from the equilibrium expression for
a heterogeneous equilibrium?
A. All gases
B. Aqueous solutes
C. Pure solids and pure liquids
D. All reactants
Answer: C. Pure solids and pure liquids
Rationale: Pure solids and pure liquids have effectively constant
activities under ordinary equilibrium calculations, so they are omitted
from K expressions. Gases and aqueous species are generally included.
Whether a species is omitted depends on its physical state and activity,
not simply whether it is a reactant or product.
8. Consider CaCO₃(s) ⇌ CaO(s) + CO₂(g). Which expression is
correct?
A. Kc = [CaO][CO₂]/[CaCO₃]
B. Kc = [CO₂]
C. Kc = [CaCO₃]/[CaO][CO₂]
D. Kc = [CaO]/[CaCO₃]
Answer: B. Kc = [CO₂]
Rationale: CaCO₃ and CaO are pure solids, so they are omitted from
the equilibrium expression. Only the gaseous CO₂ appears.
Consequently, the equilibrium constant is represented by the
equilibrium concentration of CO₂.
9. What is the primary effect of a catalyst on an equilibrium system?
A. It increases K.
B. It favors the products.
Equilibrium Practice Exam Questions
And Correct Answers (Verified
Answers) Plus Rationales 2026 Q&A |
Instant Download Pdf
1. Which statement best describes a chemical system at equilibrium?
A. The concentrations of reactants and products are equal.
B. The reaction has completely stopped.
C. The forward and reverse reactions occur at equal rates.
D. All reactants have been converted into products.
Answer: C. The forward and reverse reactions occur at equal rates.
Rationale: At dynamic equilibrium, the forward and reverse reactions
continue simultaneously, but they occur at the same rate. Because the
rates are equal, the macroscopic concentrations of reactants and
products remain constant. Equilibrium does not require equal
concentrations, nor does it mean that the reaction has stopped.
2. For the reaction N₂(g) + 3H₂(g) ⇌ 2NH₃(g), which expression
correctly represents Kc?
A. Kc = [NH₃]²/[N₂][H₂]³
B. Kc = [N₂][H₂]³/[NH₃]²
C. Kc = [NH₃]/[N₂][H₂]
D. Kc = [NH₃]²/[N₂][H₂]
Answer: A. Kc = [NH₃]²/[N₂][H₂]³
,Rationale: The equilibrium constant expression places the equilibrium
concentrations of products in the numerator and reactants in the
denominator. Each concentration is raised to the power of its
stoichiometric coefficient. Therefore, NH₃ is squared, H₂ is cubed, and
N₂ has an exponent of one.
3. What does a large value of K generally indicate for a reaction at
equilibrium?
A. The reaction is necessarily fast.
B. The equilibrium mixture contains relatively more products than
reactants.
C. The reaction has a large activation energy.
D. The reaction must be exothermic.
Answer: B. The equilibrium mixture contains relatively more
products than reactants.
Rationale: A large equilibrium constant indicates that products are
favored thermodynamically at equilibrium. It does not indicate
reaction speed, activation energy, or whether the reaction is
exothermic. A reaction can have a large K and still proceed slowly.
4. For the reaction 2SO₂(g) + O₂(g) ⇌ 2SO₃(g), what happens to the
equilibrium position when additional SO₂ is added?
A. It shifts toward reactants.
B. It remains unchanged.
C. The equilibrium constant decreases.
D. It shifts toward products.
Answer: D. It shifts toward products.
Rationale: Adding SO₂ increases the concentration of a reactant.
According to Le Châtelier’s principle, the system responds by
,consuming some of the added SO₂, shifting toward the products. At
constant temperature, the equilibrium constant itself does not change.
5. Which factor changes the numerical value of an equilibrium
constant?
A. Adding a catalyst
B. Changing the initial concentrations
C. Changing the temperature
D. Changing the amount of a pure solid
Answer: C. Changing the temperature
Rationale: Temperature is the only factor among the choices that
changes the value of K. Concentration changes can shift the
equilibrium position, but K remains constant at a fixed temperature.
Catalysts affect the rates of both forward and reverse reactions and
therefore do not change K. Pure solids are not included in the
equilibrium expression.
6. For a reaction at equilibrium, Q is calculated using the same
mathematical form as K. If Q < K, what occurs?
A. The reaction shifts toward products.
B. The reaction shifts toward reactants.
C. The reaction is already at equilibrium.
D. The reaction becomes impossible.
Answer: A. The reaction shifts toward products.
Rationale: Q compares the current composition of the system with the
equilibrium composition. If Q is smaller than K, there are relatively
too few products compared with the equilibrium condition. The
reaction therefore proceeds in the forward direction until Q reaches K.
, 7. Which substances are omitted from the equilibrium expression for
a heterogeneous equilibrium?
A. All gases
B. Aqueous solutes
C. Pure solids and pure liquids
D. All reactants
Answer: C. Pure solids and pure liquids
Rationale: Pure solids and pure liquids have effectively constant
activities under ordinary equilibrium calculations, so they are omitted
from K expressions. Gases and aqueous species are generally included.
Whether a species is omitted depends on its physical state and activity,
not simply whether it is a reactant or product.
8. Consider CaCO₃(s) ⇌ CaO(s) + CO₂(g). Which expression is
correct?
A. Kc = [CaO][CO₂]/[CaCO₃]
B. Kc = [CO₂]
C. Kc = [CaCO₃]/[CaO][CO₂]
D. Kc = [CaO]/[CaCO₃]
Answer: B. Kc = [CO₂]
Rationale: CaCO₃ and CaO are pure solids, so they are omitted from
the equilibrium expression. Only the gaseous CO₂ appears.
Consequently, the equilibrium constant is represented by the
equilibrium concentration of CO₂.
9. What is the primary effect of a catalyst on an equilibrium system?
A. It increases K.
B. It favors the products.
