chemistry : class11 Equilibrium Concentrations : Equilibrium in chemical processes : Equilibrium MCQ Questions and Answers
Practice important
Equilibrium Concentrations
MCQ questions and answers.
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MCQ Questions
1. For the reaction A(g) ⇌ B(g), the initial concentration of A is 1.0 mol L−1 and that of B is 0. At equilibrium, the concentration of A is 0.6 mol L−1. What is the equilibrium concentration of B?
A.
0.2 mol L−1
B.
0.4 mol L−1
C.
0.6 mol L−1
D.
1.6 mol L−1
Correct Answer:
0.4 mol L−1
Explanation:
A decreases from 1.0 mol L−1 to 0.6 mol L−1, so 0.4 mol L−1 of A reacts. Since the reaction ratio is 1:1, 0.4 mol L−1 of B is formed.
2. For the reaction H2(g) + I2(g) ⇌ 2HI(g), the equilibrium concentrations are [H2] = 0.2 mol L−1, [I2] = 0.2 mol L−1, and [HI] = 0.8 mol L−1. What is the equilibrium constant Kc?
A.
4
B.
8
C.
16
D.
32
Correct Answer:
16
Explanation:
For this reaction, Kc = [HI]²/([H2][I2]) = (0.8)²/(0.2 × 0.2) = 0.64/0.04 = 16.
3. For the reaction N2(g) + 3H2(g) ⇌ 2NH3(g), if 1 mol L−1 of N2 reacts completely according to the reaction ratio, how much H2 is consumed?
A.
1 mol L−1
B.
2 mol L−1
C.
3 mol L−1
D.
4 mol L−1
Correct Answer:
3 mol L−1
Explanation:
The balanced equation shows that 1 mol of N2 reacts with 3 mol of H2. Therefore, consumption of 1 mol L−1 of N2 requires 3 mol L−1 of H2.
4. For the reaction A(g) ⇌ 2B(g), the equilibrium concentration of A is 0.5 mol L−1 and 0.4 mol L−1 of A has decomposed. What is the equilibrium concentration of B if initially no B was present?
A.
0.2 mol L−1
B.
0.4 mol L−1
C.
0.8 mol L−1
D.
1.0 mol L−1
Correct Answer:
0.8 mol L−1
Explanation:
For every 1 mol of A that decomposes, 2 mol of B are formed. Thus, 0.4 mol L−1 of A produces 2 × 0.4 = 0.8 mol L−1 of B.
5. At equilibrium, the concentrations of reactants and products in a reversible reaction become:
A.
Equal to each other
B.
Constant with time
C.
Zero for the reactants
D.
Zero for the products
Correct Answer:
Constant with time
Explanation:
At equilibrium, the forward and reverse reaction rates are equal, so the concentrations of reactants and products remain constant with time, although they need not be equal.
6. For the reaction X(g) ⇌ Y(g), the initial concentration of X is 0.80 mol L−1. If 0.30 mol L−1 of X changes into Y at equilibrium, what is the equilibrium concentration of X?
A.
0.30 mol L−1
B.
0.50 mol L−1
C.
0.80 mol L−1
D.
1.10 mol L−1
Correct Answer:
0.50 mol L−1
Explanation:
The equilibrium concentration of X is its initial concentration minus the amount that reacts: 0.80 − 0.30 = 0.50 mol L−1.
7. For the reaction 2SO2(g) + O2(g) ⇌ 2SO3(g), if 0.4 mol L−1 of SO2 is consumed, how much O2 is consumed?
A.
0.1 mol L−1
B.
0.2 mol L−1
C.
0.4 mol L−1
D.
0.8 mol L−1
Correct Answer:
0.2 mol L−1
Explanation:
The reaction consumes 2 mol of SO2 for every 1 mol of O2. Therefore, consumption of 0.4 mol L−1 of SO2 requires 0.2 mol L−1 of O2.
8. For the reaction A(g) + B(g) ⇌ C(g), the equilibrium concentrations are [A] = 0.2 mol L−1, [B] = 0.3 mol L−1, and [C] = 0.6 mol L−1. What is Kc?
A.
0.5
B.
1
C.
10
D.
20
Correct Answer:
10
Explanation:
For A + B ⇌ C, Kc = [C]/([A][B]) = 0.6/(0.2 × 0.3) = 0.6/0.06 = 10.
9. In a reversible reaction, the equilibrium concentrations of reactants and products are measured after sufficient time. Which statement is correct?
A.
Only the products are present
B.
Only the reactants are present
C.
Both reactants and products may be present
D.
All substances have equal concentrations
Correct Answer:
Both reactants and products may be present
Explanation:
At chemical equilibrium, the forward and reverse reactions continue simultaneously. Therefore, both reactants and products generally remain present at constant concentrations.
10. For the reaction 2A(g) ⇌ B(g), the initial concentration of A is 1.0 mol L−1 and no B is present. If 0.4 mol L−1 of A remains unreacted at equilibrium, what is the equilibrium concentration of B?
A.
0.2 mol L−1
B.
0.3 mol L−1
C.
0.6 mol L−1
D.
1.2 mol L−1
Correct Answer:
0.3 mol L−1
Explanation:
The amount of A consumed is 1.0 − 0.4 = 0.6 mol L−1. Since 2 mol of A form 1 mol of B, the concentration of B formed is 0.6/2 = 0.3 mol L−1.