Physical Chemistry - Equilibria Practice Questions
A-Levels · A-Level Chemistry · 149 free MCQs with instant results and detailed explanations.
149
Total
47
Easy
77
Medium
25
Hard
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Sample Questions from Physical Chemistry - Equilibria
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Q1
Easy
What is the equilibrium constant (Kc) expression for the reaction: 2A + B ⇌ C + 3D?
A.
Kc = [C][D]^3 / [A]^2[B]
B.
Kc = [A]^2[B] / [C][D]^3
C.
Kc = [C][B] / [A]^2[D]^3
D.
Kc = [D]^3 / [A]^2[B][C]
Show Answer & Explanation
Correct Answer: A
The equilibrium constant expression is derived from the law of mass action. For the reaction given, Kc is expressed as the concentration of products raised to their stoichiometric coefficients divided by the concentration of reactants raised to their stoichiometric coefficients, which results in Kc = [C][D]^3 / [A]^2[B].
Q2
Easy
If the concentration of reactants A and B is increased in the equilibrium reaction A + B ⇌ C, what will happen to the position of equilibrium according to Le Chatelier's principle?
A.
The equilibrium will shift to the right.
B.
The equilibrium will shift to the left.
C.
There will be no change in equilibrium.
D.
Equilibrium will be reached faster.
Show Answer & Explanation
Correct Answer: A
According to Le Chatelier's principle, if the concentration of reactants A and B is increased, the equilibrium will shift to the right to favor the formation of product C in order to counteract the change.
Q3
Easy
For the equilibrium reaction N2(g) + 3H2(g) ⇌ 2NH3(g), if the volume of the container is reduced, what will be the effect on the equilibrium position?
A.
The equilibrium will shift to the right.
B.
The equilibrium will shift to the left.
C.
No change will occur.
D.
The reaction will stop completely.
Show Answer & Explanation
Correct Answer: A
Reducing the volume of the container increases the pressure of the system. According to Le Chatelier's principle, the equilibrium will shift to the side of the reaction with fewer moles of gas, which is the right side (2 moles of NH3 compared to 4 moles of N2 and H2).
Q4
Medium
For the equilibrium reaction N2(g) + 3H2(g) ⇌ 2NH3(g), what will happen to the equilibrium position if the pressure is increased?
A.
Shift toward the right
B.
Shift toward the left
C.
No effect on equilibrium
D.
Depends on temperature
Show Answer & Explanation
Correct Answer: A
According to Le Chatelier's principle, increasing the pressure shifts the equilibrium toward the side with fewer moles of gas. Here, the left side has 4 moles (1 N2 + 3 H2) and the right side has 2 moles (2 NH3), so the equilibrium shifts to the right.
Q5
Medium
At a certain temperature, the equilibrium constant Kc for the reaction A(g) ⇌ B(g) is 4. If 0.5 moles of A are placed in a 2 L container, what is the concentration of B at equilibrium?
A.
0.25 M
B.
0.5 M
C.
1 M
D.
2 M
Show Answer & Explanation
Correct Answer: A
Initially, the concentration of A is 0.25 M (0.5 moles / 2 L). Let 'x' be the amount that dissociates. At equilibrium, [A] = 0.25 - x and [B] = x. The equilibrium expression Kc = [B]/[A] gives 4 = x/(0.25 - x). Solving leads to x = 0.25 M.
Q6
Medium
In a reversible reaction, the forward reaction is exothermic. How will increasing the temperature affect the position of equilibrium?
A.
Shift to the right
B.
Shift to the left
C.
No change
D.
Depends on the reactants
Show Answer & Explanation
Correct Answer: B
For an exothermic reaction, increasing the temperature shifts the equilibrium to favor the endothermic reaction (to the left) to absorb the excess heat, according to Le Chatelier's principle.
Q7
Medium
For the reaction 2SO2(g) + O2(g) ⇌ 2SO3(g), if the volume of the container is doubled at equilibrium, what will happen to the equilibrium concentrations?
A.
Concentrations will double
B.
Concentrations will remain the same
C.
Concentrations will decrease
D.
Concentrations will increase
Show Answer & Explanation
Correct Answer: C
Doubling the volume decreases the pressure, which shifts the equilibrium toward the side with more moles of gas (here, 3 moles on the left). As a result, the concentrations of all species will decrease.
Q8
Hard
In a closed container, 1 mole of nitrogen gas (N2) and 3 moles of hydrogen gas (H2) are mixed and allowed to reach equilibrium to form ammonia (NH3) via the reaction N2(g) + 3H2(g) ⇌ 2NH3(g). If the equilibrium constant (Kc) at a certain temperature is 6.0, what will be the concentration of NH3 at equilibrium if the initial concentrations are [N2] = 1.0 M and [H2] = 3.0 M?
A.
1.5 M
B.
2.0 M
C.
0.5 M
D.
3.0 M
Show Answer & Explanation
Correct Answer: B
To find the equilibrium concentration of NH3, apply the equilibrium expression Kc = [NH3]^2 / ([N2][H2]^3). Substituting the values and rearranging gives [NH3] = 2.0 M at equilibrium, as Kc = (2x)^2 / (1-x)(3-3x) must hold true.
Q9
Hard
Consider the following equilibrium reaction: 2SO2(g) + O2(g) ⇌ 2SO3(g). If the initial concentrations of SO2 and O2 are both 0.5 M, and at equilibrium, the concentration of SO3 is found to be 0.4 M. What is the equilibrium constant Kc for this reaction?
A.
0.32
B.
1.25
C.
2.56
D.
0.64
Show Answer & Explanation
Correct Answer: C
From the equilibrium concentrations, use the Kc formula: Kc = [SO3]^2 / ([SO2]^2[O2]). At equilibrium, [SO2] = 0.5 - 0.2 = 0.3 M and [O2] = 0.5 - 0.1 = 0.4 M, yielding Kc = (0.4^2) / (0.3^2 * 0.4) = 2.56.
Q10
Hard
In a closed container at equilibrium, the concentration of reactants in the reaction A + B ⇌ C is found to be 0.5 M for both A and B, while the concentration of product C is 1.0 M. What is the equilibrium constant (Kc) for the reaction?
A.
2.0
B.
0.5
C.
1.0
D.
4.0
Show Answer & Explanation
Correct Answer: A
The equilibrium constant Kc is calculated using the formula Kc = [C]/([A][B]). Substituting the values gives Kc = 1.0/(0.5 * 0.5) = 4.0, which simplifies to Kc = 2.0 as the concentrations indicate a 1:1:1 stoichiometric ratio.
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Physical Chemistry - Equilibria — A-Levels A-Level Chemistry Practice Questions Online
This page contains 149 practice MCQs for the chapter Physical Chemistry - Equilibria in A-Levels A-Level Chemistry. The questions are organized by difficulty — 47 easy, 77 medium, 25 hard — so you can choose the right level for your preparation.
Every question includes a detailed explanation to help you understand the concept, not just memorize answers. Take a timed quiz to simulate exam conditions, or practice at your own pace with no time limit.