Equilibrium Practice Questions
AP (Advanced Placement) · AP Chemistry · 150 free MCQs with instant results and detailed explanations.
150
Total
47
Easy
81
Medium
22
Hard
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Sample Questions from Equilibrium
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Q1
Easy
Which of the following expressions represents the equilibrium constant (Kc) for the reaction: 2A(g) + B(g) ⇌ 3C(g)?
A.
Kc = [C]^3 / ([A]^2[B])
B.
Kc = ([A]^2[B]) / [C]^3
C.
Kc = [B] / ([A]^2[C]^3)
D.
Kc = [C]^3[B] / [A]^2
Show Answer & Explanation
Correct Answer: A
The equilibrium constant Kc is defined in terms of the concentrations of the products and reactants at equilibrium. For the reaction 2A + B ⇌ 3C, Kc = [C]^3 / ([A]^2[B]) is the correct expression.
Q2
Easy
If the equilibrium constant Kc for the reaction N2(g) + 3H2(g) ⇌ 2NH3(g) is 6.0 at a certain temperature, what can be inferred about the position of equilibrium?
A.
The formation of NH3 is favored.
B.
The decomposition of NH3 is favored.
C.
Both the forward and reverse reactions are equally favored.
D.
The reaction cannot reach equilibrium.
Show Answer & Explanation
Correct Answer: A
A Kc value greater than 1 indicates that at equilibrium, the products (NH3) are favored over the reactants (N2 and H2), thus the formation of NH3 is favored.
Q3
Easy
In which of the following scenarios will the equilibrium shift to the right (towards products) according to Le Chatelier's principle?
A.
Increasing the concentration of reactant A.
B.
Removing product B.
C.
Decreasing the temperature of an exothermic reaction.
D.
Increasing the pressure for a reaction with equal moles of gas on both sides.
Show Answer & Explanation
Correct Answer: C
For an exothermic reaction, decreasing the temperature shifts the equilibrium to the right to produce heat, favoring the formation of products.
Q4
Medium
In a closed system at equilibrium, if the concentration of reactants is increased, what will be the effect on the equilibrium position according to Le Chatelier's principle?
A.
The equilibrium shifts to the right, favoring product formation.
B.
The equilibrium shifts to the left, favoring reactant formation.
C.
The equilibrium position remains unchanged.
D.
The reaction rate decreases.
Show Answer & Explanation
Correct Answer: A
According to Le Chatelier's principle, if the concentration of a reactant is increased, the system will respond by shifting the equilibrium position to the side that consumes the added reactant, thus favoring the formation of products.
Q5
Medium
At a certain temperature, the equilibrium constant Kc for the reaction A + B ⇌ C is 4.0. If the initial concentrations of A and B are both 1.0 M, what will be the equilibrium concentration of C?
A.
0.5 M
B.
1.0 M
C.
0.25 M
D.
0.75 M
Show Answer & Explanation
Correct Answer: B
Starting with 1.0 M of A and B, let x be the amount that reacts. At equilibrium, [C] = x. Given Kc = [C]/([A][B]) = 4.0, we find that x = 1.0 M, hence [C] = 1.0 M.
Q6
Medium
Which of the following conditions will NOT affect the position of equilibrium of the reaction 2SO2(g) + O2(g) ⇌ 2SO3(g)?
A.
Increasing the pressure by decreasing volume.
B.
Adding a catalyst.
C.
Increasing the temperature.
D.
Removing SO3(g) from the system.
Show Answer & Explanation
Correct Answer: B
A catalyst increases the rate of both the forward and reverse reactions equally but does not change the position of equilibrium. Therefore, adding a catalyst will not affect the concentrations of reactants or products at equilibrium.
Q7
Medium
For the reaction N2(g) + 3H2(g) ⇌ 2NH3(g), if the volume of the container is increased, what will happen to the equilibrium concentrations of the gases?
A.
The concentration of NH3 will increase.
B.
The concentration of H2 will decrease.
C.
The concentration of N2 will decrease.
D.
The equilibrium will shift to the left.
Show Answer & Explanation
Correct Answer: D
Increasing the volume of the container decreases the pressure. According to Le Chatelier's principle, the equilibrium will shift towards the side with more gas molecules, which in this case is the left side (reactants) with 4 moles compared to 2 moles of NH3.
Q8
Hard
Consider the following equilibrium system: N2(g) + 3H2(g) ⇌ 2NH3(g). If the initial concentrations are [N2] = 1.00 M, [H2] = 3.00 M, and [NH3] = 0 M, what will be the concentration of NH3 at equilibrium if Kc = 0.500?
A.
0.50 M
B.
0.25 M
C.
0.75 M
D.
0.10 M
Show Answer & Explanation
Correct Answer: C
Using an ICE table, we set the changes as x for NH3 increase, giving us equilibrium concentrations of [N2] = 1.00 - (x/2), [H2] = 3.00 - (3x), and [NH3] = 0 + 2x. Setting up the Kc expression (0.500 = (2x)^2 / ((1.00 - x/2)(3.00 - 3x))), solves to find x. Solving yields x = 0.75 M for NH3.
Q9
Hard
At a certain temperature, the equilibrium constant Kc for the reaction 2A(g) ⇌ B(g) + C(g) is 4.0. If the initial concentration of A is 2.0 M, what is the equilibrium concentration of B?
A.
0.5 M
B.
1.0 M
C.
1.5 M
D.
2.0 M
Show Answer & Explanation
Correct Answer: B
At equilibrium, if we let x be the change in concentration of A. Then, the change in concentration of B and C will be x. The equilibrium expression is Kc = [B][C]/[A]^2, leading to 4.0 = (x)(x)/(2.0 - 2x)^2. Solving gives x = 1.0 M for B.
Q10
Hard
Consider the exothermic reaction N2(g) + 3H2(g) ⇌ 2NH3(g). If the system is at equilibrium and the temperature is increased, what would be the effect on the equilibrium position according to Le Chatelier's principle?
A.
Shifts to the right, producing more NH3.
B.
Shifts to the left, producing more N2 and H2.
C.
No change in the equilibrium position.
D.
Reaction rate increases, but equilibrium remains unchanged.
Show Answer & Explanation
Correct Answer: B
According to Le Chatelier's principle, increasing the temperature of an exothermic reaction shifts the equilibrium position to the left, favoring the reactants N2 and H2 and producing less NH3.
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Equilibrium — AP (Advanced Placement) AP Chemistry Practice Questions Online
This page contains 150 practice MCQs for the chapter Equilibrium in AP (Advanced Placement) AP Chemistry. The questions are organized by difficulty — 47 easy, 81 medium, 22 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.