• 69 questions

AP Chemistry Equilibrium Practice Test

Unofficial multiple-choice practice for Unit 7 of AP Chemistry, Equilibrium: K and Q, Le Châtelier's principle and Ksp.

What does a double arrow (⇌) between the sides of a chemical equation show?

Pick an answer, then press Check answer. Then you see Correct or Not quite, with the reason. Keys: A to D pick, Enter checks.

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Unofficial practice questions, not affiliated with the College Board. Bank checked October 9, 2026.

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All 69 questions

Topic 7.1: Introduction to equilibrium 6

  • A half-full bottle of soda is sealed and left until the pressure of CO₂ above the liquid stops rising. What are the CO₂ molecules doing then? Wikipedia, "Dynamic equilibrium"; course topic 7.1
  • A sealed flask of reacting gases has reached equilibrium. What is true of the forward and reverse reactions? Purdue University, General Chemistry Topic Review, "Gas-Phase Reactions"; course topic 7.1
  • ClNO₂ and NO are mixed in a flask with no products present. How do the two rates change as the mixture heads toward equilibrium? Purdue University, General Chemistry Topic Review, "Gas-Phase Reactions"; course topic 7.1
  • On a graph of concentration against time for a reaction that reaches equilibrium, how does the equilibrium region look? Purdue University, General Chemistry Topic Review, "Gas-Phase Reactions"; course topic 7.1
  • What does a double arrow (⇌) between the sides of a chemical equation show? Purdue University, General Chemistry Topic Review, "Gas-Phase Reactions"; course topic 7.1
  • Which observation shows that a reaction mixture has reached equilibrium? Purdue University, General Chemistry Topic Review, "Gas-Phase Reactions"; course topic 7.1
Show all 69 questions (63 more)

Topic 7.2: Direction of reversible reactions 3

  • A flask at equilibrium holds H₂, I₂ and HI. Extra HI is injected, so for a moment the reverse reaction is faster than the forward. What happens next? Purdue University, General Chemistry Topic Review, "Equilibrium Expressions"; course topic 7.2
  • At one moment the forward reaction in a closed system is faster than the reverse reaction. What is the net change at that moment? Purdue University, General Chemistry Topic Review, "Equilibrium Expressions"; course topic 7.2
  • Only the products of a reversible reaction are placed in a flask. Which rate is zero at that instant? Purdue University, General Chemistry Topic Review, "Gas-Phase Reactions"; course topic 7.2

Topic 7.3: Reaction quotient and equilibrium constant 6

  • For 2 NO₂(g) ⇌ N₂O₄(g), which is the Kp expression? Purdue University, General Chemistry Topic Review, "Equilibrium Expressions"; course topic 7.3
  • For 2 SO₂(g) + O₂(g) ⇌ 2 SO₃(g), a mixture has [SO₂] = 0.20 M, [O₂] = 0.10 M and [SO₃] = 0.40 M. What is Qc? Purdue University, General Chemistry Topic Review, "Equilibrium Expressions"; course topic 7.3
  • For H₂(g) + I₂(g) ⇌ 2 HI(g), a flask holds much HI and only a trace of H₂ and I₂. What can be said about Qc? Purdue University, General Chemistry Topic Review, "Equilibrium Expressions"; course topic 7.3
  • Limestone breaks down on heating: CaCO₃(s) ⇌ CaO(s) + CO₂(g). What is the Kp expression? Wikipedia, "Calcium carbonate"; course topic 7.3
  • The reaction quotient Q and the equilibrium constant K are written in the same form. How do they differ? Purdue University, General Chemistry Topic Review, "Equilibrium Expressions"; course topic 7.3
  • What is the Kc expression for N₂(g) + 3 H₂(g) ⇌ 2 NH₃(g)? Purdue University, General Chemistry Topic Review, "Equilibrium Expressions"; course topic 7.3

Topic 7.4: Calculating the equilibrium constant 5

  • 2.00 mol of SO₃ is placed in a 1.00 L flask. At equilibrium 0.40 mol of O₂ is present. What is Kc for 2 SO₃(g) ⇌ 2 SO₂(g) + O₂(g)? Purdue University, General Chemistry Topic Review, "Equilibrium Expressions"; course topic 7.4
  • At equilibrium a flask holds [H₂] = 0.020 M, [I₂] = 0.020 M and [HI] = 0.16 M. What is Kc for H₂(g) + I₂(g) ⇌ 2 HI(g) at this temperature? Purdue University, General Chemistry Topic Review, "Equilibrium Expressions"; course topic 7.4
  • At equilibrium P(NO₂) = 0.50 atm and P(N₂O₄) = 1.5 atm. What is Kp for 2 NO₂(g) ⇌ N₂O₄(g) at this temperature? Purdue University, General Chemistry Topic Review, "Equilibrium Expressions"; course topic 7.4
  • PCl₅ starts at 0.100 M with no products present and decomposes: PCl₅(g) ⇌ PCl₃(g) + Cl₂(g). At equilibrium [Cl₂] = 0.040 M. What is Kc? Purdue University, General Chemistry Topic Review, "Equilibrium Expressions"; course topic 7.4
  • Two flasks at the same temperature hold the same reaction at equilibrium, but they were filled with different starting amounts. What must be the same in both? Purdue University, General Chemistry Topic Review, "Equilibrium Expressions"; course topic 7.4

Topic 7.5: Magnitude of the equilibrium constant 4

  • 2 NO(g) + O₂(g) ⇌ 2 NO₂(g) has Kc = 3 × 10⁶ at 200 °C. What does a K this large say about the equilibrium mixture? Purdue University, General Chemistry Topic Review, "Equilibrium Expressions"; course topic 7.5
  • At room temperature the equilibrium for N₂ + 3 H₂ ⇌ 2 NH₃ favors ammonia, yet a mixture of the two gases makes none that can be detected. Why? Wikipedia, "Haber process"; course topic 7.5
  • Four reactions of the form A(g) + B(g) ⇌ C(g) + D(g) have the Kc values below. Which goes furthest toward products? College Board, AP Chemistry Course and Exam Description, topic 7.5
  • N₂(g) + O₂(g) ⇌ 2 NO(g) has Kc = 2.3 × 10⁻¹⁹ at 200 °C. What does this predict for a mixture of N₂ and O₂ held at that temperature? Purdue University, General Chemistry Topic Review, "Equilibrium Expressions"; course topic 7.5

Topic 7.6: Properties of the equilibrium constant 5

  • At a certain temperature 2 SO₂(g) + O₂(g) ⇌ 2 SO₃(g) has Kc = 4.0 × 10². What is Kc for SO₃(g) ⇌ SO₂(g) + ½ O₂(g)? College Board, AP Chemistry Course and Exam Description, topic 7.6
  • At a certain temperature H₂(g) + I₂(g) ⇌ 2 HI(g) has Kc = 49. What is Kc for ½ H₂(g) + ½ I₂(g) ⇌ HI(g) at that temperature? College Board, AP Chemistry Course and Exam Description, topic 7.6
  • ClNO₂(g) + NO(g) ⇌ NO₂(g) + ClNO(g) has Kc = 1.3 × 10⁴ at 25 °C. What is Kc for the reverse reaction at 25 °C? Purdue University, General Chemistry Topic Review, "Equilibrium Expressions"; course topic 7.6
  • Every coefficient in a balanced equation is doubled. What happens to Q for a given mixture? College Board, AP Chemistry Course and Exam Description, topic 7.6
  • N₂(g) + O₂(g) ⇌ 2 NO(g) has constant K₁, and 2 NO(g) + O₂(g) ⇌ 2 NO₂(g) has constant K₂. What is K for N₂(g) + 2 O₂(g) ⇌ 2 NO₂(g)? Purdue University, General Chemistry Topic Review, "Equilibrium Expressions"; course topic 7.6

Topic 7.7: Calculating equilibrium concentrations 6

  • 2 SO₃(g) ⇌ 2 SO₂(g) + O₂(g) has Kc = 1.6 × 10⁻¹⁰ at 300 °C. Starting from 0.100 M SO₃, which assumption makes the calculation manageable? Purdue University, General Chemistry Topic Review, "Equilibrium Expressions"; course topic 7.7
  • At a certain high temperature N₂(g) + O₂(g) ⇌ 2 NO(g) has Kc = 4.0 × 10⁻⁶. A flask starts with 0.50 M N₂ and 0.50 M O₂. What is [NO] at equilibrium? Wikipedia, "ICE table"; course topic 7.7
  • At a certain temperature H₂(g) + I₂(g) ⇌ 2 HI(g) has Kc = 50. A mixture has [H₂] = 0.10 M, [I₂] = 0.10 M and [HI] = 0.50 M. Which way does it go? Purdue University, General Chemistry Topic Review, "Equilibrium Expressions"; course topic 7.7
  • At a certain temperature H₂(g) + I₂(g) ⇌ 2 HI(g) has Kc = 64. A flask starts with 1.00 M H₂ and 1.00 M I₂ and no HI. What is [HI] at equilibrium? Wikipedia, "ICE table"; course topic 7.7
  • For N₂(g) + 3 H₂(g) ⇌ 2 NH₃(g), [N₂] falls by x on the way to equilibrium. How does [NH₃] change? Purdue University, General Chemistry Topic Review, "Equilibrium Expressions"; course topic 7.7
  • PCl₅(g) ⇌ PCl₃(g) + Cl₂(g) has Kc = 0.030 at 250 °C. A mixture at that temperature has Qc = 0.30. What happens as it moves to equilibrium? Purdue University, General Chemistry Topic Review, "Equilibrium Expressions"; course topic 7.7

Topic 7.8: Representations of equilibrium 4

  • A particle drawing of A(g) ⇌ B(g) at equilibrium shows 2 particles of A and 8 particles of B in one box. What is K? College Board, AP Chemistry Course and Exam Description, topic 7.8
  • A(g) ⇌ B(g) has K = 1.0. A particle drawing of a mixture shows 9 A and 3 B. What will a drawing made at equilibrium show? College Board, AP Chemistry Course and Exam Description, topic 7.8
  • For A₂(g) + B₂(g) ⇌ 2 AB(g), a particle drawing at equilibrium shows 1 A₂, 1 B₂ and 6 AB in one box. What is K? College Board, AP Chemistry Course and Exam Description, topic 7.8
  • Two particle drawings show the same sealed mixture at equilibrium, one minute apart. How do they compare? Wikipedia, "Chemical equilibrium"; course topic 7.8

Topic 7.9: Introduction to Le Châtelier's principle 9

  • 2 NO₂(g) ⇌ N₂O₄(g) is exothermic. NO₂ is brown and N₂O₄ is colorless. A sealed tube of the mixture is moved from room temperature into hot water. What is seen? Purdue University, General Chemistry Topic Review, "Equilibrium Expressions"; course topic 7.9
  • A pink solution of cobalt(II) chloride in water turns blue when concentrated hydrochloric acid is added. Which added ion drives the shift? Wikipedia, "Cobalt(II) chloride"; course topic 7.9
  • A rigid vessel holds N₂, H₂ and NH₃ at equilibrium. Helium is then let in. What does the helium do to the amounts of the three gases? Wikipedia, "Le Chatelier's principle"; course topic 7.9
  • Ammonia is taken out of a mixture of N₂, H₂ and NH₃ at equilibrium, and the yield of the reaction goes up. Why? Wikipedia, "Haber process"; course topic 7.9
  • An iron catalyst is added to a mixture of N₂, H₂ and NH₃. What does it change? Wikipedia, "Le Chatelier's principle"; course topic 7.9
  • H₂(g) + I₂(g) ⇌ 2 HI(g) is at equilibrium. The container's volume is halved at constant temperature. What happens to the position of equilibrium? Wikipedia, "Le Chatelier's principle"; course topic 7.9
  • Making ammonia from N₂ and H₂ is exothermic, so a cold reactor would give the best equilibrium yield. Why is the process run hot anyway? Wikipedia, "Le Chatelier's principle"; course topic 7.9
  • N₂(g) + 3 H₂(g) ⇌ 2 NH₃(g) at equilibrium is compressed to a smaller volume at constant temperature. Which way does it shift, and why? Purdue University, General Chemistry Topic Review, "Le Chatelier's Principle"; course topic 7.9
  • N₂(g) + 3 H₂(g) ⇌ 2 NH₃(g) has settled in a rigid vessel. Extra N₂ is injected. Once the mixture settles again, how does [H₂] compare with its earlier value? Purdue University, General Chemistry Topic Review, "Le Chatelier's Principle"; course topic 7.9

Topic 7.10: Reaction quotient and Le Châtelier's principle 5

  • 2 NO₂(g) ⇌ N₂O₄(g) has Kp = 7.1 at 25 °C. At equilibrium P(NO₂) = 0.10 atm and P(N₂O₄) = 0.071 atm. The volume is suddenly halved, doubling both pressures. What follows? Purdue University, General Chemistry Topic Review, "Equilibrium Expressions"; course topic 7.10
  • The blood-red equilibrium Fe³⁺(aq) + SCN⁻(aq) ⇌ FeSCN²⁺(aq) is diluted with water to twice its volume. How does Q compare with K just after, and which way does it shift? Wikipedia, "Thiocyanate"; course topic 7.10
  • More of a reactant is added to a system at equilibrium at constant temperature. Which is true the instant after? Purdue University, General Chemistry Topic Review, "Le Chatelier's Principle"; course topic 7.10
  • N₂O₄(g) ⇌ 2 NO₂(g) is endothermic. What does heating the mixture do to K? Wikipedia, "Le Chatelier's principle"; course topic 7.10
  • Which stress changes the value of K itself? Purdue University, General Chemistry Topic Review, "Le Chatelier's Principle"; course topic 7.10

Topic 7.11: Introduction to solubility equilibria 10

  • A salt has a Ksp greater than 1. How do the solubility rules class it? College Board, AP Chemistry Course and Exam Description, topic 7.11
  • A saturated solution of NaCl sits over undissolved crystals. What is true of the system? Purdue University, General Chemistry Topic Review, "Solubility"; course topic 7.11
  • A saturated solution of silver chromate, Ag₂CrO₄, holds 6.5 × 10⁻⁵ mol of the salt per liter. What is Ksp? Wikipedia, "Silver chromate"; course topic 7.11
  • AgCl has Ksp = 1.8 × 10⁻¹⁰ and AgBr has Ksp = 5.0 × 10⁻¹³. Which is more soluble in water, in moles per liter? Purdue University, General Chemistry Topic Review, "Solubility Product"; Ksp of AgCl from its "Common Ions and Complex Ions" page; course topic 7.11
  • AgCl has Ksp = 1.8 × 10⁻¹⁰ and Ag₂CrO₄ has Ksp = 1.1 × 10⁻¹². Which is more soluble in water, in moles per liter? Purdue University, General Chemistry Topic Review, "Solubility Product"; Ksp of AgCl from its "Common Ions and Complex Ions" page, of Ag₂CrO₄ from Wikipedia, "Silver chromate"; course topic 7.11
  • Barium sulfate (233.4 g/mol) has Ksp = 1.1 × 10⁻¹⁰ at 25 °C. About how many milligrams of it dissolve in one liter of pure water? Wikipedia, "Barium sulfate"; course topic 7.11
  • Equal volumes of 2.0 × 10⁻⁴ M AgNO₃ and 2.0 × 10⁻⁴ M NaCl are mixed. Ksp for AgCl is 1.8 × 10⁻¹⁰. Does AgCl precipitate? Purdue University, General Chemistry Topic Review, "Solubility Product"; Ksp of AgCl from its "Common Ions and Complex Ions" page; course topic 7.11
  • Lead(II) iodide, PbI₂, has Ksp = 4.4 × 10⁻⁹ at 20 °C. What is its molar solubility in pure water? Wikipedia, "Lead(II) iodide"; course topic 7.11
  • More solid AgCl is stirred into a saturated AgCl solution that already has solid at the bottom. What happens to [Ag⁺]? Purdue University, General Chemistry Topic Review, "Solubility Product"; course topic 7.11
  • What is the Ksp expression for silver chromate, Ag₂CrO₄(s) ⇌ 2 Ag⁺(aq) + CrO₄²⁻(aq)? Purdue University, General Chemistry Topic Review, "Solubility Product"; course topic 7.11

Topic 7.12: Common-ion effect 6

  • A student measures the solubility of AgCl but uses tap water that contains chloride in place of distilled water. How is the result affected? Wikipedia, "Common-ion effect"; course topic 7.12
  • Barium sulfate has Ksp = 1.1 × 10⁻¹⁰. What is its molar solubility in 0.010 M Na₂SO₄? Wikipedia, "Solubility equilibrium"; course topic 7.12
  • CaF₂ has Ksp = 4.0 × 10⁻¹¹. Is CaF₂ less soluble in 0.10 M NaF or in 0.10 M Ca(NO₃)₂? Purdue University, General Chemistry Topic Review, "Solubility Product"; course topic 7.12
  • How soluble is AgCl in 0.10 M NaCl compared with pure water? Purdue University, General Chemistry Topic Review, "Common Ions and Complex Ions"; course topic 7.12
  • Lead(II) iodide, PbI₂, has Ksp = 4.4 × 10⁻⁹. What is its molar solubility in 0.10 M KI? Wikipedia, "Common-ion effect"; course topic 7.12
  • Solid NaCl is dissolved in a saturated solution of AgCl at constant temperature. What happens to Ksp and to [Ag⁺]? Purdue University, General Chemistry Topic Review, "Solubility Product"; course topic 7.12

How this list was compiled: Our own questions, written to Unit 7 (Equilibrium) of the College Board's AP Chemistry Course and Exam Description, effective fall 2024, https://apcentral.collegeboard.org/media/pdf/ap-chemistry-course-and-exam-description.pdf, read 2026-10-09. Each fact and each constant was read on 2026-10-09 in the public page named under its question: the General Chemistry Topic Review of Purdue University, Wikipedia and the course description itself. Every calculated answer was worked a second time from the numbers in the question. Licence: Own work. Short quotations from the public documents named under each question.

How it works

This AP Chemistry equilibrium practice test has 69 questions of our own on Unit 7, from the equilibrium constant to solubility. It is unofficial, and it is not affiliated with or endorsed by the College Board, the owner of AP.

Read the full guide

What Unit 7 covers

The College Board's course description, read October 9, 2026, gives Unit 7 twelve topics and no weights among them, so the spread is ours: introduction to equilibrium (6 questions), direction of reversible reactions (3), Q and K (6), calculating K (5), magnitude of K (4), properties of K (5), equilibrium concentrations (6), particle drawings (4), Le Châtelier's principle (9), Q and Le Châtelier (5), solubility equilibria (10) and the common-ion effect (6).

Constants and sources

A question prints every K and Ksp it needs. The values and rules were read in a Purdue University chemistry review, a Wikipedia article or the course description, named under each answer, and every calculated answer was worked twice.

  • Write Q exactly as you write K, then compare. Q below K runs forward; Q above K runs in reverse.
  • Only temperature changes K. More reactant, a new volume or a catalyst leaves K where it was.
  • Rank salts by Ksp only when they share an ion ratio. For AgCl against Ag₂CrO₄, work out each solubility.

Questions and answers

What unit is equilibrium in AP Chem?

Unit 7, Equilibrium, the seventh of nine units. The course description allows about 13 to 15 class periods for it, and the acid-base equilibria follow in Unit 8.

How much of the AP Chemistry exam is equilibrium?

Unit 7 is 7 to 9% of the multiple-choice section, by the College Board's course page. That section has 60 questions in 1 hour 30 minutes and is half of the exam score.

Do you have to convert between Kc and Kp on the AP Chemistry exam?

No. The course description says converting between Kc and Kp is not assessed. You should know how the two differ and notice which one a question uses.

Is Ksp part of the AP Chemistry equilibrium unit?

Yes. Topics 7.11 and 7.12 cover Ksp, molar solubility and the common-ion effect. How pH changes solubility comes in Unit 8, and the free energy of dissolution in Unit 9.

Is this the AP Chemistry Unit 7 Progress Check?

No. The Progress Check is the College Board's own set, given through AP Classroom. The questions on this page are our own, written from the Unit 7 topic list, and none copies or rewords a real exam question.

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