AP Chemistry Practice Quiz: Properties of the Equilibrium Constant

Written by AP Content Team, Verified for 2026 AP Exams, Last updated: May 2026

Test your understanding with short quizzes. This quiz has 11 questions to check your progress.

Question 1 of 11

Consider the generic equilibrium reaction: A(g) ⇌ B(g), which has an equilibrium constant, K, of 5.0. What is the value of the equilibrium constant for the reverse reaction, B(g) ⇌ A(g)?

A)5.0B)-5.0C)0.20D)25

All Questions (11)

Consider the generic equilibrium reaction: A(g) ⇌ B(g), which has an equilibrium constant, K, of 5.0. What is the value of the equilibrium constant for the reverse reaction, B(g) ⇌ A(g)?

A) 5.0

B) -5.0

C) 0.20

D) 25

Correct Answer: C

According to the rules for manipulating equilibrium constants, when a reaction is reversed, the new equilibrium constant (K_new) is the inverse of the original constant (K_orig). Therefore, K_new = 1 / K_orig = 1 / 5.0 = 0.20.

The equilibrium constant, K, for the reaction 2SO₂(g) + O₂(g) ⇌ 2SO₃(g) is 4.0. What is the equilibrium constant for the reaction SO₂(g) + ½O₂(g) ⇌ SO₃(g) at the same temperature?

A) 2.0

B) 4.0

C) 8.0

D) 16.0

Correct Answer: A

The second reaction's stoichiometric coefficients are the first reaction's coefficients multiplied by a factor of ½. When the coefficients are multiplied by a factor 'c', the new equilibrium constant is the original K raised to the power of c. Here, K_new = K^(½) = (4.0)^(½) = √4.0 = 2.0.

Given the following elementary steps for a reaction: Step 1: A + B ⇌ C, K₁ = 2.0 Step 2: C + D ⇌ E, K₂ = 3.0 What is the equilibrium constant, K_overall, for the overall reaction A + B + D ⇌ E?

A) 0.67

B) 1.0

C) 5.0

D) 6.0

Correct Answer: D

When reactions are added together to form an overall reaction, the equilibrium constant for the overall reaction is the product of the equilibrium constants for the individual steps. Therefore, K_overall = K₁ × K₂ = 2.0 × 3.0 = 6.0.

The equilibrium constant for the reaction H₂(g) + I₂(g) ⇌ 2HI(g) is K. If the reaction is manipulated to become 2HI(g) ⇌ H₂(g) + I₂(g), the new equilibrium constant is 1/K. Given that the mathematical forms for K and the reaction quotient Q are identical, how would the reaction quotient for the forward reaction (Q) relate to the reaction quotient for the reversed reaction (Q') under the same set of non-equilibrium conditions?

A) Q' = 1 / Q

B) Q' = -Q

C) Q' = Q²

D) Q' = Q

Correct Answer: A

The expressions for K and Q have identical mathematical forms. Therefore, any valid algebraic manipulation of K, such as inverting it for a reversed reaction, also applies to Q. If K_rev = 1/K_fwd, then Q_rev = 1/Q_fwd.

The equilibrium constant for the reaction N₂(g) + 3H₂(g) ⇌ 2NH₃(g) is K = 36. What is the equilibrium constant for the reaction NH₃(g) ⇌ ½N₂(g) + ³/₂H₂(g)?

A) 1/6

B) 1/18

C) 1/36

D) 1/72

Correct Answer: A

This requires two manipulations. First, reverse the original reaction: 2NH₃(g) ⇌ N₂(g) + 3H₂(g), for which K' = 1/K = 1/36. Second, multiply the coefficients of this reversed reaction by ½. This raises the new constant to the power of ½: K_new = (K')^(½) = (1/36)^(½) = 1/6.

Given the following equilibrium reactions and their constants: 1. A(g) + B(g) ⇌ C(g) K₁ = 15 2. D(g) ⇌ C(g) K₂ = 3.0 What is the equilibrium constant for the reaction A(g) + B(g) ⇌ D(g)?

A) 45

B) 18

C) 12

D) 5.0

Correct Answer: D

To obtain the target reaction, we must add reaction 1 to the reverse of reaction 2. The reverse of reaction 2 is C(g) ⇌ D(g), and its equilibrium constant is K₂' = 1/K₂ = 1/3.0. When the reactions are added, the overall K is the product of the individual constants: K_overall = K₁ × K₂' = 15 × (1/3.0) = 5.0.

A chemist represents a complex chemical process as a sum of several elementary reaction steps. How is the overall equilibrium expression for the multistep process related to the equilibrium expressions of the constituent steps?

A) The overall K is the sum of the K values for the individual steps.

B) The overall K is the product of the K values for the individual steps.

C) The overall K is the average of the K values for the individual steps.

D) The overall K is determined only by the K value of the slowest step.

Correct Answer: B

When individual reactions are added together to yield an overall reaction, the equilibrium constant for the resulting overall reaction is the product of the equilibrium constants (K's) for the reactions that were summed.

Given the following reactions at a certain temperature: 1. H₂(g) + I₂(g) ⇌ 2HI(g) K₁ = 50 2. N₂(g) + 3H₂(g) ⇌ 2NH₃(g) K₂ = 1.0 × 10⁵ Determine the equilibrium constant, K, for the reaction: 2NH₃(g) + 3I₂(g) ⇌ N₂(g) + 6HI(g)

A) 5.0 × 10⁶

B) 2.0 × 10⁻¹⁰

C) 1.25

D) 8.0 × 10⁻¹

Correct Answer: C

To get the target equation, we must manipulate the given reactions. First, reverse reaction 2: 2NH₃ ⇌ N₂ + 3H₂, K₂' = 1/K₂ = 1/(1.0 × 10⁵) = 1.0 × 10⁻⁵. Second, multiply reaction 1 by 3: 3H₂ + 3I₂ ⇌ 6HI, K₁' = (K₁)³ = 50³ = 1.25 × 10⁵. Finally, add the two new reactions. The 3H₂ cancels out. The overall K is the product of the manipulated constants: K_overall = K₂' × K₁' = (1.0 × 10⁻⁵) × (1.25 × 10⁵) = 1.25.

The equilibrium constant for the reaction 2NO(g) + Cl₂(g) ⇌ 2NOCl(g) is K = 4.0 × 10⁴. What is the value of K for the reaction 4NO(g) + 2Cl₂(g) ⇌ 4NOCl(g)?

A) 8.0 × 10⁴

B) 2.0 × 10²

C) 4.0 × 10⁸

D) 1.6 × 10⁹

Correct Answer: D

The second reaction is obtained by multiplying the stoichiometric coefficients of the first reaction by a factor of 2. When coefficients are multiplied by a factor 'c', the equilibrium constant is raised to the power of c. Therefore, K_new = K² = (4.0 × 10⁴)² = 16 × 10⁸ = 1.6 × 10⁹.

The overall reaction X + 2Y ⇌ Z has an overall equilibrium constant K_overall = 80. The reaction proceeds via two steps: Step 1: X + Y ⇌ W, K₁ = 20 Step 2: W + Y ⇌ Z, K₂ = ? What is the value of the equilibrium constant, K₂, for the second step?

A) 1600

B) 60

C) 4

D) 0.25

Correct Answer: C

The overall reaction is the sum of Step 1 and Step 2. Therefore, the overall equilibrium constant is the product of the constants for each step: K_overall = K₁ × K₂. We can solve for K₂: K₂ = K_overall / K₁ = 80 / 20 = 4.

Given the following equilibrium reactions: 1. N₂O₄(g) ⇌ 2NO₂(g) K₁ = 0.21 2. 2NO(g) + O₂(g) ⇌ 2NO₂(g) K₂ = 4.0 × 10¹³ What is the equilibrium constant for the reaction 2NO(g) + O₂(g) ⇌ N₂O₄(g)?

A) 8.4 × 10¹²

B) 4.0 × 10¹³

C) 5.2 × 10⁻¹⁵

D) 1.9 × 10¹⁴

Correct Answer: D

To obtain the target reaction, we must combine the given reactions. We can use reaction 2 as written. We must reverse reaction 1 to get 2NO₂(g) ⇌ N₂O₄(g). The constant for this reversed reaction is K₁' = 1/K₁ = 1/0.21. Adding reaction 2 and the reversed reaction 1 cancels out 2NO₂(g). The overall K is the product of the constants: K_overall = K₂ × K₁' = (4.0 × 10¹³) × (1/0.21) ≈ 1.9 × 10¹⁴.