chemistry : class11 Equilibrium Constant : Equilibrium in chemical processes : Equilibrium MCQ Questions and Answers
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Equilibrium Constant
MCQ questions and answers.
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MCQ Questions
1. For the reaction N2(g) + 3H2(g) ⇌ 2NH3(g), which expression represents the equilibrium constant Kc?
A.
[NH3]^2 / ([N2][H2]^3)
B.
([N2][H2]^3) / [NH3]^2
C.
[NH3] / ([N2][H2])
D.
[N2][H2] / [NH3]
Correct Answer:
[NH3]^2 / ([N2][H2]^3)
Explanation:
For a reaction, the equilibrium constant is written as the product concentrations raised to their stoichiometric coefficients divided by the reactant concentrations raised to their coefficients.
2. In the equilibrium expression for Kc, which substances are generally omitted?
A.
Gases
B.
Aqueous substances
C.
Pure solids and pure liquids
D.
All reactants
Correct Answer:
Pure solids and pure liquids
Explanation:
The concentrations of pure solids and pure liquids remain effectively constant, so they are not included in the equilibrium constant expression.
3. For the reaction H2(g) + I2(g) ⇌ 2HI(g), the equilibrium constant Kc is expressed as:
A.
[HI]^2 / ([H2][I2])
B.
[H2][I2] / [HI]^2
C.
[HI] / ([H2][I2])
D.
[H2][I2] / [HI]
Correct Answer:
[HI]^2 / ([H2][I2])
Explanation:
The concentration of HI is squared because its coefficient in the balanced equation is 2. The reactant concentrations appear in the denominator.
4. What does a large value of Kc generally indicate for a reaction at equilibrium?
A.
Reactants are strongly favored
B.
Products are strongly favored
C.
Reactants and products are present in exactly equal amounts
D.
The reaction cannot reach equilibrium
Correct Answer:
Products are strongly favored
Explanation:
A large equilibrium constant means that the concentration of products is relatively large compared with the concentration of reactants at equilibrium.
5. For the reaction A(g) ⇌ B(g), if the equilibrium constant is Kc, what is the equilibrium constant for B(g) ⇌ A(g)?
A.
Kc
B.
Kc + 1
C.
1 / Kc
D.
2Kc
Correct Answer:
1 / Kc
Explanation:
When a chemical equation is reversed, the new equilibrium constant is the reciprocal of the original equilibrium constant.
6. For the reaction 2A(g) ⇌ 2B(g), if the equilibrium constant is Kc, what is the equilibrium constant for A(g) ⇌ B(g)?
A.
Kc
B.
2Kc
C.
Kc^2
D.
√Kc
Correct Answer:
√Kc
Explanation:
When all coefficients in a balanced equation are divided by 2, the new equilibrium constant is the square root of the original equilibrium constant.
7. For the reaction CaCO3(s) ⇌ CaO(s) + CO2(g), which is the correct expression for Kc?
A.
[CaO][CO2] / [CaCO3]
B.
[CO2]
C.
[CaCO3] / ([CaO][CO2])
D.
[CaO] / [CO2]
Correct Answer:
[CO2]
Explanation:
Pure calcium carbonate and pure calcium oxide are solids and are omitted from the equilibrium expression. Therefore, Kc is determined only by the concentration of carbon dioxide.
8. For the equilibrium reaction 2SO2(g) + O2(g) ⇌ 2SO3(g), which change would alter the numerical value of Kc?
A.
Adding more SO2
B.
Removing some SO3
C.
Changing the temperature
D.
Changing the volume
Correct Answer:
Changing the temperature
Explanation:
The value of the equilibrium constant for a particular reaction changes when the temperature changes. Changes in concentration or volume may shift equilibrium but do not change Kc at a fixed temperature.
9. For the reaction A(g) ⇌ B(g) + C(g), the equilibrium constant Kc is:
A.
[A] / ([B][C])
B.
[B][C] / [A]
C.
[A][B] / [C]
D.
[C] / ([A][B])
Correct Answer:
[B][C] / [A]
Explanation:
The products B and C appear in the numerator, while the reactant A appears in the denominator. Each concentration is raised to the power of its coefficient, which is 1 here.
10. If Kc for a reaction is much less than 1, what does this generally mean?
A.
The equilibrium mixture contains mostly products
B.
The equilibrium mixture contains mostly reactants
C.
The reaction has no reactants
D.
The reaction is always complete
Correct Answer:
The equilibrium mixture contains mostly reactants
Explanation:
A very small equilibrium constant indicates that the reactants are favored over the products at equilibrium.