Quick answer: At chemical equilibrium the forward and reverse reaction rates are equal, so concentrations stay constant. This AP Chemistry test on chemical equilibrium has 8 questions worth 20 marks, to do in 45 minutes: writing K, reaction quotient and ICE table. The mark scheme is on a separate page; free printable PDF.
This test lasts 45 minutes and covers K and Q, ICE tables, Kp and Kc, and Le Chatelier’s principle. A calculator is allowed. Use R = 0.08206 L atm mol⁻¹ K⁻¹ when needed. Show your working; the total is 20 marks.
Level: AP Chemistry · Curriculum: AP Chem Unit 7
Question 1 Writing K (2 marks)
Write Kc for each.- 2 NO(g) + O₂(g) ⇌ 2 NO₂(g) (1 mark)
- CaCO₃(s) ⇌ CaO(s) + CO₂(g) (1 mark)
Question 2 Reaction quotient (3 marks)
N₂(g) + 3 H₂(g) ⇌ 2 NH₃(g) has Kc = 0.50 at a certain temperature. A mixture has [N₂] = 0.50 M, [H₂] = 0.20 M and [NH₃] = 0.10 M.- Calculate Q. (2 marks)
- Predict the direction of change. (1 mark)
Question 3 ICE table (3 marks)
2 HI(g) ⇌ H₂(g) + I₂(g), Kc = 1/64 = 0.0156. Start with 0.80 M HI. Calculate the equilibrium concentrations of all species.Question 4 Le Chatelier (2 marks)
N₂O₄(g) ⇌ 2 NO₂(g), ΔH > 0. State the direction of shift for each.- Raise the temperature. (1 mark)
- Compress the gas mixture. (1 mark)
Question 5 Catalyst and inert gas (2 marks)
Explain why adding a catalyst, or adding argon at constant volume, does not shift an equilibrium.Question 6 Kp and Kc (3 marks)
PCl₅(g) ⇌ PCl₃(g) + Cl₂(g). At equilibrium at 500 K, P(PCl₅) = 0.40 atm and P(PCl₃) = P(Cl₂) = 0.60 atm.- Calculate Kp. (1 mark)
- Calculate Kc using R = 0.08206 L atm mol⁻¹ K⁻¹. (2 marks)
Question 7 Reading a disturbance (3 marks)
- Identify the disturbance at 10 s. (1 mark)
- State the direction of the shift and justify it from the graph. (1 mark)
- State what happens to K. (1 mark)
Question 8 Temperature and K (2 marks)
For an exothermic reaction, K = 100 at 300 K. Predict whether K at 500 K is greater or smaller, and explain.
