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 H2(g) + I2(g) ⇌ 2HI(g), which expression represents the equilibrium constant Kc?
A.
Kc = [H2][I2] / [HI]2
B.
Kc = [HI]2 / ([H2][I2])
C.
Kc = [HI] / ([H2][I2])
D.
Kc = [H2][I2][HI]2
Correct Answer:
Kc = [HI]2 / ([H2][I2])
Explanation:
For a reaction, the equilibrium constant is the product of equilibrium concentrations raised to their stoichiometric coefficients, divided by the corresponding reactant concentrations.
2. For the reaction N2(g) + 3H2(g) ⇌ 2NH3(g), what is the expression for Kc?
A.
Kc = [NH3]2 / ([N2][H2]3)
B.
Kc = [N2][H2]3 / [NH3]2
C.
Kc = [NH3] / ([N2][H2])
D.
Kc = [N2][H2] / [NH3]
Correct Answer:
Kc = [NH3]2 / ([N2][H2]3)
Explanation:
The powers in the Kc expression are the stoichiometric coefficients in the balanced chemical equation: 2 for NH3, 1 for N2, and 3 for H2.
3. For the equilibrium reaction 2SO2(g) + O2(g) ⇌ 2SO3(g), which substances appear in the denominator of the Kc expression?
A.
Only SO3
B.
Only SO2
C.
SO2 and O2
D.
SO3 and O2
Correct Answer:
SO2 and O2
Explanation:
Reactants appear in the denominator of the equilibrium constant expression, while products appear in the numerator.
4. What does a large value of Kc generally indicate for a reaction at equilibrium?
A.
The reaction mixture contains mostly reactants
B.
The reaction mixture contains mostly products
C.
The reaction has stopped completely
D.
The reaction has no reactants
Correct Answer:
The reaction mixture contains mostly products
Explanation:
A large equilibrium constant means the concentration of products is relatively high compared with that of reactants at equilibrium.
5. What does a very small value of Kc generally indicate for a reaction at equilibrium?
A.
Products are strongly favored
B.
Reactants are strongly favored
C.
Reactants and products are always present in equal amounts
D.
The reaction cannot occur
Correct Answer:
Reactants are strongly favored
Explanation:
A very small Kc means the numerator containing product concentrations is small relative to the denominator containing reactant concentrations.
6. For the reaction CaCO3(s) ⇌ CaO(s) + CO2(g), which expression represents Kc?
A.
Kc = [CaO][CO2] / [CaCO3]
B.
Kc = [CaCO3] / ([CaO][CO2])
C.
Kc = [CO2]
D.
Kc = [CaCO3][CaO][CO2]
Correct Answer:
Kc = [CO2]
Explanation:
Pure solids are not included in the equilibrium constant expression, so only the concentration of gaseous CO2 appears.
7. For the reaction H2(g) + Cl2(g) ⇌ 2HCl(g), what happens to the equilibrium constant expression if the reaction is written in the reverse direction?
A.
It remains unchanged
B.
It becomes the reciprocal of the original expression
C.
It becomes zero
D.
It becomes the square of the original expression
Correct Answer:
It becomes the reciprocal of the original expression
Explanation:
Reversing a chemical equation changes the equilibrium constant from Kc to 1/Kc.
8. If the balanced equation for a reaction is multiplied by 2, how is its equilibrium constant related to the original equilibrium constant Kc?
A.
It becomes 2Kc
B.
It becomes Kc/2
C.
It becomes Kc2
D.
It remains Kc
Correct Answer:
It becomes Kc2
Explanation:
When all coefficients in a balanced equation are multiplied by a factor, the new equilibrium constant is raised to that factor.
9. Which quantity is used in the expression for the concentration equilibrium constant Kc?
A.
Equilibrium concentrations of the reacting species
B.
Initial masses of the reacting species
C.
Melting points of the reacting species
D.
Volumes of the reaction vessel only
Correct Answer:
Equilibrium concentrations of the reacting species
Explanation:
Kc is calculated using the concentrations of reactants and products when the system has reached equilibrium.
10. For the reaction 2NO2(g) ⇌ N2O4(g), which expression gives Kc?
A.
Kc = [NO2]2 / [N2O4]
B.
Kc = [N2O4] / [NO2]2
C.
Kc = [N2O4] / [NO2]
D.
Kc = [NO2][N2O4]
Correct Answer:
Kc = [N2O4] / [NO2]2
Explanation:
The product N2O4 is placed in the numerator, and the reactant NO2 is placed in the denominator with its stoichiometric coefficient, 2, as the exponent.