chemistry : class11 Law of Mass Action : Equilibrium in chemical processes : Equilibrium MCQ Questions and Answers
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Law of Mass Action
MCQ questions and answers.
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MCQ Questions
1. According to the law of mass action, the rate of a reaction is proportional to the product of the active masses of the reactants, each raised to a power equal to its
A.
Atomic mass
B.
Stoichiometric coefficient
C.
Molecular mass
D.
Valency
Correct Answer:
Stoichiometric coefficient
Explanation:
The law of mass action states that the reaction rate depends on the concentrations of reactants, with each concentration raised to the power of its stoichiometric coefficient.
2. For the reaction H₂(g) + I₂(g) ⇌ 2HI(g), the equilibrium constant in terms of concentration is
A.
Kc = [HI]² / ([H₂][I₂])
B.
Kc = [H₂][I₂] / [HI]²
C.
Kc = [HI] / ([H₂][I₂])
D.
Kc = [H₂]²[I₂]² / [HI]
Correct Answer:
Kc = [HI]² / ([H₂][I₂])
Explanation:
The concentrations of products are written in the numerator and those of reactants in the denominator, each raised to its stoichiometric coefficient.
3. For the reaction N₂(g) + 3H₂(g) ⇌ 2NH₃(g), which expression represents Kc?
A.
Kc = [N₂][H₂]³ / [NH₃]²
B.
Kc = [NH₃]² / ([N₂][H₂]³)
C.
Kc = [NH₃] / ([N₂][H₂])
D.
Kc = [NH₃]³ / ([N₂]²[H₂])
Correct Answer:
Kc = [NH₃]² / ([N₂][H₂]³)
Explanation:
For a balanced reaction, product concentrations form the numerator and reactant concentrations form the denominator, with powers equal to their coefficients.
4. For the reaction CaCO₃(s) ⇌ CaO(s) + CO₂(g), which species is included in the equilibrium constant expression?
A.
CaCO₃(s)
B.
CaO(s)
C.
CO₂(g)
D.
Both CaCO₃(s) and CaO(s)
Correct Answer:
CO₂(g)
Explanation:
The active masses of pure solids are taken as constant and are omitted from the equilibrium expression. Therefore, only gaseous CO₂ appears.
5. For the reaction 2SO₂(g) + O₂(g) ⇌ 2SO₃(g), the equilibrium constant Kc is written as
A.
[SO₃]² / ([SO₂]²[O₂])
B.
[SO₂]²[O₂] / [SO₃]²
C.
[SO₃] / ([SO₂][O₂])
D.
[SO₃]² / ([SO₂][O₂]²)
Correct Answer:
[SO₃]² / ([SO₂]²[O₂])
Explanation:
The coefficients in the balanced equation become the powers in the equilibrium expression: 2 for SO₂, 1 for O₂, and 2 for SO₃.
6. In the law of mass action, the term active mass of a gaseous substance is commonly represented by its
A.
Colour
B.
Concentration
C.
Molar mass
D.
Melting point
Correct Answer:
Concentration
Explanation:
For dilute systems and equilibrium calculations, the active mass of a dissolved or gaseous substance is represented by its concentration.
7. For the reaction A(g) + B(g) ⇌ C(g), the equilibrium constant Kc is
A.
[A][B] / [C]
B.
[C] / ([A][B])
C.
[A][C] / [B]
D.
[B][C] / [A]
Correct Answer:
[C] / ([A][B])
Explanation:
The concentration of the product C is placed in the numerator, while the concentrations of reactants A and B are placed in the denominator.
8. For the reaction 2A(g) ⇌ B(g), which is the correct expression for Kc?
A.
[A]² / [B]
B.
[B] / [A]²
C.
[B]² / [A]
D.
[A] / [B]²
Correct Answer:
[B] / [A]²
Explanation:
The product B appears in the numerator with power 1, and reactant A appears in the denominator with power 2, matching the balanced equation.
9. For the reaction H₂(g) + Cl₂(g) ⇌ 2HCl(g), which concentration term is raised to the power of 2 in Kc?
A.
[H₂]
B.
[Cl₂]
C.
[HCl]
D.
All concentration terms
Correct Answer:
[HCl]
Explanation:
HCl has a stoichiometric coefficient of 2 in the balanced equation, so its concentration is squared in the equilibrium constant expression.
10. For the reaction PCl₅(g) ⇌ PCl₃(g) + Cl₂(g), the equilibrium constant Kc is
A.
[PCl₅] / ([PCl₃][Cl₂])
B.
[PCl₃][Cl₂] / [PCl₅]
C.
[PCl₃] / ([PCl₅][Cl₂])
D.
[Cl₂] / ([PCl₅][PCl₃])
Correct Answer:
[PCl₃][Cl₂] / [PCl₅]
Explanation:
The products PCl₃ and Cl₂ are placed in the numerator, and the reactant PCl₅ is placed in the denominator according to the law of mass action.