AP Chemistry Exam Unit 7 Practice Test 2025 (Equilibrium)

Last Updated on January 13, 2025

AP Chemistry Exam Unit 7 Practice Test 2025 (Equilibrium). We freely provide this AP Chemistry Unit 5: Atomic Structure and Properties Multiple Choice Questions and Answers and Free-Response Questions. This unit is 7%–9% of the Advanced Placement (AP) Exam score.

You’ll explore various questions about methods to observe the changes occurring during a chemical reaction, the factors influencing reaction rate, and how they relate to a series of elementary reactions. This online quiz engages subject reviews, covering Introduction to Equilibrium to Introduction to solubility equilibria.

Table of Contents

AP Chemistry Exam Unit 7 Practice Test

AP Chemistry Unit 7: Equilibrium

AP Chemistry Practice Test
Unit 7: Equilibrium
Total Items: 25 (Multiple Choice Questions)

Unit 7: Equilibrium

You’ll chart how chemical reactions change over time, what causes substances to reach equilibrium, and how systems react when that equilibrium is disturbed.

Topics may include:

Introduction to equilibrium
Calculating the equilibrium constant
Calculating equilibrium concentrations
Introduction to Le Châtelier’s principle
Introduction to solubility equilibria

On The Exam

7%–9% of exam score

1 / 23

A catalyst will NOT

(A) increase the forward reaction rate

(B) shift the equilibrium to favor the products

(D) increase the speed at which equilibrium will be achieved

2 / 23

The effect of changing the temperature on a chemical system is best determined using

(A) K_a, Q, and the enthalpy of reaction

(B) Ks_sp and Le Châtelier’s principle

(D) K_c and Le Châtelier’s principle

3 / 23

How can you determine if a system has come to equilibrium?

(A) By calculating Q and the direction toward equilibrium

(B) If K_sp is equal to Heisenberg’s uncertainty principle

(D) By comparing to see if K_c = K_p

4 / 23

A chemical system in equilibrium will

(A) have the same concentrations of all products and reactants

(B) form more products if the temperature is increased

(D) not have any precipitates

5 / 23

Using logical estimates, in which of the following expressions can the variable x be assumed to be either much smaller than or much larger than the other term(s) to simplify the mathematics?

(A) x[C]

(B) [C] – x

(D) ax² – bx + c

6 / 23

Note the following reaction:

heat + 2NO₂(g) ⇌ N₂O₄(g)

Which change will not be effective in increasing the amount of N₂O₄(g)

(A) Decreasing the volume of the reaction vessel

(B) Increasing the temperature

(D) Absorbing the N₂O₄(g) with a solid absorbant

7 / 23

The reaction

2NO₂(g) ⇌ N₂O₄(g)

has an equilibrium constant of 4.5 × 10³ at a certain temperature. What is the equilibrium constant of

2N₂O₄(g) ⇔ 4NO₂(g) ?

(A) 9.0 × 10⁶

(B) 4.5 × 10³

(D) 4.9 × 10^-8

8 / 23

The correct form of the solubility product for silver sulfate, Ag₂SO₄, is

(A)

(B)

(C)

(D)

9 / 23

In the following concentration versus time curve, at what time has this reaction reached equilibrium?

(A) Before 1 minute

(B) Between 1 and 3 minutes

(D) After 6 minutes

10 / 23

Which is an appropriate formulation of the equilibrium expression for the reaction

(A)

(B)

(C)

(D)

11 / 23

In the reaction

2HI(g) ⇌ H₂(g) + l₂(g)

the equilibrium constant is 0.020. If 0.200 mol of HI are placed in a 10.0 L flask, how many moles of I₂(g) will be in the flask when equilibrium is reached?

(A) 0.0022 mol

(B) 0.022 mol

(D) 2.2 mol

12 / 23

For the reaction

2NO₂(g) ⇌ N₂O₄(g)

K_p = 8.8 when pressures are measured in atmospheres. Under which of the following conditions will the reaction proceed in the forward direction?

(A)

(B)

(C)

(D)

13 / 23

The solubility product of PbI2 is 7.9 × 10^–9. What is the molar solubility of PbI₂ in a solution that has 2.0 x 10^-3 molar KI?

(A) 2.0 × 10^-3 M

(B) 4.0 x 10^-6 M

(D) 8.9 × 10^-5 M

14 / 23

Consider the concentration versus time curve in question 9. If we call the reactants A and B and the products X and Y, what is the most reasonable chemical equation to describe this reaction?

(A) 2A + 2B ⇌ X + Y

(B) 2A + 3B ⇌ X + 2Y

(D) A + 2B ⇌ X + 2Y

15 / 23

When pure liquids and/or solids are part of a chemical equation, they are not included in the equilibrium expression for that equation. Why?

(A) The concentrations of all pure liquids and solids are defined as 1.00.

(B) Pure substances react very slowly unless ground to a fine powder.

(D) The concentration of a solid or of a liquid at a given temperature and pressure is always a constant no matter how much of the substance is present.

16 / 23

Look at questions 9 and 14. Estimate the equilibrium constant for that reaction if the concentration at equilibrium of the bottom line in the graph represents 0.10 M.

(A) 3.7

(B) 0.27

(D) 1.0 × 10^-2

17 / 23

In which of the following cases is the reaction expected to be endothermic.

(A) Increasing the pressure increases the amount of product formed.

(B) Increasing the amount of reactants increases the amount of product formed.

(D) Increasing the volume decreases the amount of product formed.

18 / 23

A reaction has a very large equilibrium constant of 3.3 × 10¹³. Which statement is NOT true about this reaction?

(A) The reaction is very fast.

(B) The reaction is essentially complete.

(D) The equilibrium constant will change if the temperature is changed.

19 / 23

The K_sp of AgCl is 1.8 × 10^–10, and the K_sp of AgI is 8.3 × 10^–17. A solution is 0.100 M in I⁻ and Cl⁻. When a silver nitrate solution is slowly added to this mixture, what is the molarity of iodide ions when AgCl just starts to precipitate?

(A) 1.0 × 10^-5 M

(B) 8.3 × 10^-7 M

(D) 9.1 × 10^-9 M

20 / 23

A certain reaction is known to be endothermic. A temperature jump experiment is run where the system at equilibrium is rapidly heated a few degrees Celsius and then allowed to cool back to room temperature. The concentrations of the reactants and products are monitored. The following concentration versus time graphs were obtained for all species in the mixture.

(A) A + B ⇌ C + D

(B) 2A + B ⇌ C + D

(D) C + D ⇌ 2A + B

21 / 23

The equilibrium constant for the reaction

H₂(g) + l₂(g) ⇌ 2HI(g)

must be determined. If 1.00 g of HI is placed in a 2.00 L flask, which of the following is LEAST important in determining the equilibrium constant?

(A) The temperature must remain constant at the desired value.

(B) Several measurements must be made to assure that the reaction is at ‐ equilibrium.

(D) All three concentrations must be accurately measured.

22 / 23

In an experiment 0.00300 mol each of SO₃(g), SO₂(g), and O₂(g) were placed in a 10.0 L flask at a certain temperature. When the reaction came to equilibrium, the concentration of SO₂(g) in the flask was 3.50 × 10^–5
M. What is K_c for the reaction.

2SO₂(g) + O₂(g) ⇌ 2SO₃₍g)

(A) 1.9 × 10⁷

(B) 3.5 × 10^-5

(D) 1.2 × 10^-9

23 / 23

The weak acid H2A ionizes in two steps with these equilibrium constants:

H₂A ⇌ H⁺ + HA^- K_a1 = 2.3 × 10^-4

HA^- ⇌ H⁺ + A^2- K_a2 = 4.5 × 10^-7

What is the equilibrium constant for the reaction:

H₂A ⇌ 2H⁺ + A^2-

(A) 6.8 × 10^-11

(B) 1.0 × 10^-10

(D) 2.0 × 10^-3

Your score is

Free-Response Questions

Use the principles and techniques of chemical equilibrium to answer the following questions.

1. When performing equilibrium calculations, it is possible to make simplifying assumptions. These assumptions are based in one case on the mathematical principles behind using significant figures in calculations. In a second case, the assumptions are based on an experimental principle of making a measurement.

(a) Explain how an understanding of significant figures allows you to make a simplification and give an example.
(b) Explain how the simplifying assumption often relates to an understanding of a measurement process.

(a) The solubility product of HgI₂ is 1.1 × 10^–28.
(i) What is the molar solubility of HgI₂?
(ii) What is the molar solubility if HgI₂ is dissolved in 0.000250 molar NaI solution?

(b) At a certain temperature the reaction of hydrogen and chlorine to produce hydrogen chloride, all in the gas phase, has an equilibrium constant of 265. If 25.0 g of HCl are placed in a 150 L vessel and allowed to come to equilibrium, what will the concentrations of all species be?

(c) The gas-phase reaction between oxygen and sulfur dioxide has an equilibrium constant of 8.8 ×10¹⁴ at a certain temperature. If 23.4 g of sulfur trioxide are placed in a 20.0 L vessel, calculate the concentration of all species at equilibrium.