Unit 7: Equilibrium
Practice AP Chemistry Unit 7 — Kc, Kp, ICE tables, reaction quotient, Le Chatelier's principle, and Ksp. Build FRQ skills for equilibrium calculations.
What Unit 7 Covers in AP Chemistry
Equilibrium is one of the most concept-dense and calculation-intensive units in AP Chemistry. It is also one of the most heavily tested — equilibrium reasoning appears not just in Unit 7 questions but also in acid-base and electrochemistry FRQs later in the course.
Core Topics in Unit 7
- Equilibrium constant expressions — Writing Kc and Kp expressions from balanced equations; understanding why pure solids and liquids are excluded
- Relationship between Kc and Kp — Converting between Kc and Kp using the ideal gas law relationship and delta-n
- ICE tables — Setting up and solving ICE (Initial, Change, Equilibrium) tables for both Kc and Ksp calculations
- Reaction quotient Q — Calculating Q and comparing it to K to predict the direction a reaction will shift to reach equilibrium
- Le Chatelier's principle — Predicting the effect of changes in concentration, pressure, volume, and temperature on equilibrium position and on K itself
- Solubility product constant Ksp — Calculating molar solubility from Ksp; predicting precipitate formation using the ion product
AP FRQ Patterns: Equilibrium Calculations
A standard AP equilibrium FRQ gives you an initial concentration, a K value, and asks you to find equilibrium concentrations using an ICE table. Many students lose points by setting up the ICE table correctly but then making algebra errors. Practice solving the quadratic approximation and knowing when the approximation is valid (when K is very small).
AP FRQ Patterns: Le Chatelier Reasoning
Le Chatelier questions ask you to predict a shift and then explain the result in terms of Q vs. K. A complete AP-style response states the direction of the shift, identifies which species increase or decrease, and explains whether the K value itself changes (it only changes with temperature). Responses that only say 'the reaction shifts right' without justification earn minimal credit.
Common Mistakes in Unit 7
- Including pure solids or pure liquids in equilibrium expressions
- Confusing a shift in equilibrium position with a change in K — only temperature changes K
- Setting up ICE tables with the wrong stoichiometric coefficients in the Change row
- Calculating Q and comparing it to K in the wrong direction when predicting the shift