plumiKc and Kp expressions and calculations: OCR A‑Level Chemistry A questions
OCR A-Level Chemistry A past-paper questions on 5.1.2.2 Kc and Kp expressions and calculations, 2016–2025, with mark schemes and examiner’s reports where available.
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Q17(c)(i)
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All 21 questions on Kc and Kp expressions and calculations, as a list
- June 2025, Paper 1, Q17(c)(i) (1 mark): Explain why Kp for Equilibrium 17.3 has no units. [1]
- June 2025, Paper 1, Q17(c)(ii) (3 marks): An equal number of moles of steam and carbon monoxide are left at 700 K in a sealed container until equilibrium is reached. At equilibrium, both H2 and CO2 have
- June 2024, Paper 1, Q18(a)(i) (5 marks): 2.25 moles of SO3 is heated to 550 °C in the presence of a catalyst and the resulting mixture allowed to reach equilibrium. The equilibrium mixture contains 0.9
- June 2023, Paper 1, Q19(a)(i) (5 marks): A sealed flask containing 6.00 moles of NO2(g) is heated to a constant temperature and allowed to reach equilibrium. The equilibrium mixture contains 5.40 mol o
- June 2023, Paper 3, Q6(d) (5 marks): In the UK, most sulfuric acid, H2SO4, is manufactured by the Contact process. One stage in the Contact process involves the equilibrium between sulfur dioxide,
- June 2022, Paper 1, Q20(a) (6 marks): This question is about equilibria involving hydrogen. (a)* Hydrogen is used industrially to manufacture ammonia. The equilibrium is shown below. 2NH3(g) ∆H = –9
- November 2021, Paper 1, Q20(c)(i) (4 marks): Calculate Kp, in MPa–1, for Equilibrium 20.1. Give your answer to 3 significant figures. Kp = MPa–1 [4]
- November 2021, Paper 3, Q1(b) (2 marks): Pure PCl5 is placed in a sealed container which is heated to 200 ºC. An equilibrium is set up: PCl5(g) PCl3(g) + Cl2(g) Under these conditions: Kc = 8.00 × 10–3
- November 2020, Paper 1, Q9 (1 mark): The reversible reaction of nitrogen and hydrogen to form ammonia is shown below. N2(g) + 3H2(g) 2NH3(g) In the equilibrium mixture, the partial pressure of N2 i
- November 2020, Paper 1, Q17(d) (3 marks): At 298 K, the free energy change, ∆G, for the production of methanol in equilibrium 1 is −2.48 × 104 J mol−1. ∆G is linked to Kp by the relationship: ∆G = −RT l
- November 2020, Paper 1, Q20(b) (4 marks): The student carries out a second experiment to determine the value of Kc for this reaction. The student mixes 9.6 g of CH3OH with 12.0 g of CH3COOH and adds the
- June 2019, Paper 1, Q19(b)(ii) (5 marks): Determine the value of Kp for Equilibrium 1 at 1000 K. Show all your working. Give your answer to 3 significant figures. Kp = [5]
- June 2018, Paper 1, Q18(a) (2 marks): Write an expression for Kc for this equilibrium and state the units. Kc = Units = [2]
- June 2018, Paper 1, Q18(b) (4 marks): A chemist mixes together nitrogen and oxygen and pressurises the gases so that their total gas volume is 4.0 dm3. • The mixture is allowed to reach equilibrium
- June 2018, Paper 3, Q5(b)(iv) (1 mark): Kc is the equilibrium constant in terms of equilibrium concentrations. Why can expression 5.1 be used to calculate Kc for this equilibrium? [1]
- June 2018, Paper 3, Q5(b)(v) (3 marks): Calculate the value of Kc for this reaction. Show your working. Kc = [3]
- June 2017, Paper 1, Q18(b)(i) (1 mark): Why is equilibrium 18.1 a heterogeneous equilibrium? [1]
- June 2017, Paper 1, Q18(b)(ii) (1 mark): Write the expression for Kp for equilibrium 18.1. [1]
- June 2017, Paper 1, Q20(b)(i) (2 marks): Write the expression for Kc and the units of Kc for this equilibrium. [2]
- June 2017, Paper 1, Q20(b)(ii) (4 marks): Determine the amount, in mol, of SO3 in the equilibrium mixture at this temperature. Give your final answer to an appropriate number of significant figures. Sho
- June 2017, Paper 3, Q3(c)(ii) (3 marks): Peroxyethanoic acid can be prepared by reacting hydrogen peroxide with ethanoic acid. This is a heterogeneous equilibrium. CH3COOOH(aq) + H2O(l) Kc = 0.37 dm3 m
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