AP Chemistry — Unit 7: Equilibrium

What AP Chemistry Unit 7 covers

The College Board Course and Exam Description breaks Unit 7 into 14 topics:

1. 7.1 Introduction to Equilibrium
2. 7.2 Direction of Reversible Reactions
3. 7.3 Reaction Quotient and Equilibrium Constant
4. 7.4 Calculating the Equilibrium Constant
5. 7.5 Magnitude of the Equilibrium Constant
6. 7.6 Properties of the Equilibrium Constant
7. 7.7 Calculating Equilibrium Concentrations
8. 7.8 Representations of Equilibrium
9. 7.9 Introduction to Le Chatelier's Principle
10. 7.10 Reaction Quotient and Le Chatelier's Principle
11. 7.11 Introduction to Solubility Equilibria
12. 7.12 Common-Ion Effect
13. 7.13 pH and Solubility
14. 7.14 Free Energy of Dissolution

AP Chemistry Unit 7 practice questions

• What does it mean for a chemical equilibrium to be 'dynamic'?

  Forward and reverse reactions keep occurring at equal rates. There's no net change, but the system never truly stops.

• A sealed bottle of sparkling water sits unopened. CO₂ gas and dissolved CO₂ are present. What observable sign confirms equilibrium has been reached?

  No observable change occurs over time in the sealed system. Concentrations and partial pressures of all species stay constant.

• At a given moment, the forward reaction rate in a reversible system is greater than the reverse rate. What happens to the concentrations of reactants and products?

  Reactant concentrations fall and product concentrations rise until rates match. Net change stops once forward and reverse rates become equal.

• How does a system behave differently when the reverse rate exceeds the forward rate versus when both rates are equal?

  When reverse > forward: net conversion of products to reactants occurs. When rates are equal: equilibrium is established and concentrations stay constant.

• For the reaction aA + bB ⇌ cC + dD, what is the expression for Kc (the equilibrium constant in terms of concentration)?

  Kc = [C]^c[D]^d / [A]^a[B]^b. Products go on top, reactants on the bottom, each raised to its coefficient.

• Why are pure solids and pure liquids excluded from equilibrium constant expressions?

  Their concentration is constant regardless of how much is present. So pure solids and liquids don't affect Q or K.

• For N₂ + 3H₂ ⇌ 2NH₃, at equilibrium: [N₂] = 0.50 M, [H₂] = 0.20 M, [NH₃] = 0.60 M. What is Kc?

  Kc = (0.60)²/[(0.50)(0.20)³] = 90. This is [NH₃]² over [N₂][H₂]³.

• For a gas-phase reaction, what does Kp use instead of molar concentrations, and how is the expression structured?

  Kp uses each gas's partial pressure raised to its coefficient, just like Kc. Same form as Kc, but with pressures: Kp = (P_C)^c(P_D)^d / (P_A)^a(P_B)^b.

+ 32 more AP Chemistry cards in the app.

Key terms in Unit 7

These 12 terms show up in the Unit 7 cards. Each one links to its definition in the AP Chemistry key-term reference.

• Acid-base reaction
• Common-ion effect
• ICE table
• Ionic solid
• Le Chatelier's principle
• Molar solubility
• Partial pressure
• Reaction rate
• Solubility
• Stoichiometry
• Thermodynamics
• ΔG° = ΔH° − TΔS°