Chemical equilibria, Le Chatelier’s principle and Kc: AQA A‑Level Chemistry questions

Every AQA A-Level Chemistry exam question on 3.1.6 Chemical equilibria, Le Chatelier’s principle and Kc, 2016–2025, with its mark scheme and examiner’s report.

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2,301 questions

Q04.5
June 2025 · Paper 1
2 marks3.1.6 Chemical equilibria, Le Chatelier’s principle and Kc
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Q04.1
June 2025 · Paper 3
1 mark3.1.6 Chemical equilibria, Le Chatelier’s principle and Kc
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Q04.2
June 2025 · Paper 3
2 marks3.1.6 Chemical equilibria, Le Chatelier’s principle and Kc
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Q04.3
June 2025 · Paper 3
6 marks3.1.6 Chemical equilibria, Le Chatelier’s principle and Kc
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Q07.1
June 2025 · AS Paper 1
2 marks3.1.6 Chemical equilibria, Le Chatelier’s principle and Kc
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Q07.2
June 2025 · AS Paper 1
3 marks3.1.6 Chemical equilibria, Le Chatelier’s principle and Kc
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Q07.3
June 2025 · AS Paper 1
6 marks3.1.6 Chemical equilibria, Le Chatelier’s principle and Kc
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Q15
June 2025 · AS Paper 1
1 mark3.1.6 Chemical equilibria, Le Chatelier’s principle and Kc
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Q04.3
June 2024 · Paper 1
1 mark3.1.6 Chemical equilibria, Le Chatelier’s principle and Kc
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Q02.1
June 2024 · Paper 2
2 marks3.1.6 Chemical equilibria, Le Chatelier’s principle and Kc
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Q02.2
June 2024 · Paper 2
4 marks3.1.6 Chemical equilibria, Le Chatelier’s principle and Kc
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Q02.3
June 2024 · Paper 2
2 marks3.1.6 Chemical equilibria, Le Chatelier’s principle and Kc
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Q07.6
June 2024 · AS Paper 2
1 mark3.1.6 Chemical equilibria, Le Chatelier’s principle and Kc
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Q07.7
June 2024 · AS Paper 2
4 marks3.1.6 Chemical equilibria, Le Chatelier’s principle and Kc
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Q07.8
June 2024 · AS Paper 2
3 marks3.1.6 Chemical equilibria, Le Chatelier’s principle and Kc
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Q04.4
June 2023 · Paper 1
2 marks3.1.6 Chemical equilibria, Le Chatelier’s principle and Kc 3.1.10 Equilibrium constant Kp for homogeneous systems
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Q04.5
June 2023 · Paper 1
2 marks3.1.6 Chemical equilibria, Le Chatelier’s principle and Kc
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Q13
June 2023 · Paper 3
1 mark3.1.6 Chemical equilibria, Le Chatelier’s principle and Kc
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Q25
June 2023 · Paper 3
1 mark3.1.6 Chemical equilibria, Le Chatelier’s principle and Kc
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Q08.1
June 2023 · AS Paper 1
2 marks3.1.6 Chemical equilibria, Le Chatelier’s principle and Kc
The whole paper ↗

All 90 questions on Chemical equilibria, Le Chatelier’s principle and Kc, as a list

June 2025, Paper 1, Q04.5 (2 marks): Some ammonia and oxygen are reacted and the mixture is left to reach equilibrium at a fixed temperature. Explain why increasing the temperature of this equilibr
June 2025, Paper 3, Q04.1 (1 mark): Give the expression for the equilibrium constant, Kc, for the equilibrium. [1 mark] Kc
June 2025, Paper 3, Q04.2 (2 marks): Before the titration, the sample is ‘quenched’ by adding 50 cm3 of ice-cold water. Suggest why the sample is ‘quenched’ in this way before the titration. Explai
June 2025, Paper 3, Q04.3 (6 marks): The amount of I–(aq) in the equilibrium mixture is found to be 3.00 × 10–4 mol Calculate the value of Kc at 40 °C for the equilibrium. 2 Fe3+(aq) + 2 I–(aq) ⇌ 2
June 2025, AS Paper 1, Q07.1 (2 marks): Draw a line on Figure 1 to show how the concentration of hydrogen iodide changes with time. [2 marks]
June 2025, AS Paper 1, Q07.2 (3 marks): State and explain the effect of increasing the temperature on the equilibrium yield of hydrogen iodide. [3 marks] Effect on yield Explanation
June 2025, AS Paper 1, Q07.3 (6 marks): Give an expression for the equilibrium constant, Kc, for this reaction. Calculate a value for the equilibrium constant at this fixed temperature. Give the units
June 2025, AS Paper 1, Q15 (1 mark): Which equilibrium has a lower yield of product when the pressure in the system is increased at constant temperature? [1 mark] A 2 NOCl(g) ⇌ 2 NO(g) + Cl2(g) B 2
June 2024, Paper 1, Q04.3 (1 mark): The temperature of the equilibrium mixture formed in Question 04.1 is increased. How does the amount of H2(g) change when the new position of equilibrium is rea
June 2024, Paper 2, Q02.1 (2 marks): Calculate the amount, in moles, of P before the reaction with Q. Use your answer to calculate the concentration, in mol dm–3, of P in the initial 25.0 cm3 sampl
June 2024, Paper 2, Q02.2 (4 marks): Give the expression for the equilibrium constant, Kc Calculate the value of Kc and deduce its units. [4 marks] Kc Value of Kc Units
June 2024, Paper 2, Q02.3 (2 marks): Explain why the amount of S increases when water is added to the equilibrium mixture. [2 marks]
June 2024, AS Paper 2, Q07.6 (1 mark): Give an expression for the equilibrium constant (Kc) for this reaction. [1 mark] Kc =
June 2024, AS Paper 2, Q07.7 (4 marks): Table 3 shows the amount of each substance in an equilibrium mixture in a container of volume 1.20 dm3 at a constant temperature. Table 3 Substance C2H4(g) H2O(
June 2024, AS Paper 2, Q07.8 (3 marks): Predict the effect of increasing the temperature on the yield of propanoic acid. Explain your answer. [3 marks] Effect on yield Explanation Section B Answer all
June 2023, Paper 1, Q04.4 (2 marks): The equilibrium mixture in Question 04.3 is compressed into a smaller volume. Deduce the effect, if any, of this change on the equilibrium yield of oxygen and o
June 2023, Paper 1, Q04.5 (2 marks): The equilibrium mixture in Question 04.3 is allowed to reach equilibrium at a lower temperature. Explain why the equilibrium yield of oxygen decreases. [2 marks
June 2023, Paper 3, Q13 (1 mark): When HF is added to water at 298 K, this equilibrium is established. HF(aq) ⇌ H+(aq) + F–(aq) At equilibrium, [HF] = 7.70 × 10–3 mol dm–3 and [F–] = 2.30 × 10–3
June 2023, Paper 3, Q25 (1 mark): Which statement about catalysts used in reactions at equilibrium, at a constant temperature, is correct? [1 mark] A They are always used in the solid state. B T
June 2023, AS Paper 1, Q08.1 (2 marks): A solution containing 0.60 mol of A is added to a solution containing 0.60 mol of B. The amount of C formed at equilibrium is 0.28 mol Deduce the amounts, in mo
June 2023, AS Paper 1, Q08.2 (1 mark): Give an expression for the equilibrium constant (Kc) for this reaction. [1 mark] Kc
June 2023, AS Paper 1, Q08.3 (3 marks): The temperature of the equilibrium mixture is decreased. Predict the effect, if any, on the value of Kc Give a reason for your prediction. [3 marks] Prediction
June 2023, AS Paper 1, Q08.4 (3 marks): In another mixture at equilibrium [A] = 0.48 mol dm–3 [C] = 0.62 mol dm–3 For this reaction, the equilibrium constant Kc = 7.8 mol–2 dm6 Calculate [B] at equili
June 2023, AS Paper 2, Q16 (1 mark): Which statement about the industrial production of ethanol from ethene at 300 °C is correct? C2H4(g) + H2O(g) ⇌ C2H5OH(g) ΔH= –46 kJ mol –1 [1 mark] A An increa
June 2022, Paper 1, Q01.1 (2 marks): Give two features of a reaction in dynamic equilibrium. [2 marks] Feature 1 Feature 2
June 2022, Paper 1, Q01.2 (1 mark): A gas-phase reaction is at equilibrium. When the pressure is increased the yield of product decreases. State what can be deduced about the chemical equation for
June 2022, Paper 2, Q02.1 (2 marks): Calculate the amount, in moles, of C2F4 and of HCl in the equilibrium mixture. [2 marks] Amount of C2F4 mol Amount of HCl mol
June 2022, Paper 2, Q02.2 (1 mark): Give an expression for Kc for this equilibrium. [1 mark] Kc
June 2022, Paper 2, Q02.3 (3 marks): Calculate a value for Kc Give its units. [3 marks] Kc Units
June 2022, Paper 2, Q02.4 (3 marks): State and explain the effect of using a higher temperature on the equilibrium yield of tetrafluoroethene. [3 marks] Effect on yield Explanation
June 2022, AS Paper 1, Q07.1 (2 marks): Explain how Figure 1 shows that the forward reaction in this equilibrium is exothermic. [2 marks]
June 2022, AS Paper 1, Q07.2 (3 marks): State whether the forward reaction in this equilibrium results in an increase, decrease or no change in the amount, in moles, of gas. Explain your answer. [3 ma
June 2022, AS Paper 1, Q07.3 (1 mark): Explain why using a catalyst has no effect on the percentage yield. [1 mark]
June 2022, AS Paper 1, Q07.4 (5 marks): At 745 K, 0.150 dm3 of an equilibrium mixture contains 0.0285 mol of hydrogen and 0.0870 mol of nitrogen. Calculate the amount, in moles, of ammonia present in
June 2022, AS Paper 1, Q07.5 (2 marks): Calculate the value, at 745 K, for the equilibrium constant Kc for this dissociation of ammonia to give hydrogen and nitrogen. State the units. 2 NH3(g) ⇌ 3 H2(
June 2022, AS Paper 2, Q18 (1 mark): The reaction reaches equilibrium in a container of fixed volume. Which is the expression for Kc for this equilibrium? [1 mark] A Kc = [CH3OH] [CO] + [H2]2 B Kc
June 2022, AS Paper 2, Q19 (1 mark): 2.0 mol of carbon monoxide is mixed with 3.0 mol of hydrogen and allowed to reach equilibrium. The equilibrium mixture contains 0.6 mol of methanol. What is the
June 2022, AS Paper 2, Q20 (1 mark): Which change in condition will decrease the equilibrium yield of methanol? [1 mark] A Increase the amount of CO in the equilibrium mixture. B Increase the press
November 2021, Paper 1, Q05.1 (3 marks): State and explain the effect, if any, of a decrease in overall pressure on the equilibrium yield of SO3 [3 marks] Effect Explanation
November 2021, Paper 2, Q05.1 (3 marks): 1 mol of a diester with molecular formula C7H12O4 is added to 1 mol of water in the presence of a small amount of catalyst. The mixture is left to reach equilib
November 2021, Paper 2, Q05.3 (3 marks): A new equilibrium mixture of the substances from Question 05.1 is prepared at a different temperature. C7H12O4(l) + 2 H2O(l) ⇌ 2 CH3COOH(l) + HO(CH2)3OH(l) Tabl
November 2021, Paper 3, Q20 (1 mark): Which statement about the addition of a catalyst to an equilibrium mixture is correct? [1 mark] A The activation energy for the reverse reaction increases. B Th
November 2021, AS Paper 1, Q09 (6 marks): Hydrogen can be prepared on an industrial scale using the reversible reaction between methane and steam. CH4(g) + H2O(g) ⇌ CO(g) + 3 H2(g) ΔH = +206 kJ mol−1 Th
November 2021, AS Paper 1, Q10.1 (1 mark): Give an expression for the equilibrium constant (Kc) for this reaction. [1 mark] Kc
November 2021, AS Paper 1, Q10.2 (3 marks): A mixture of sulfur dioxide and oxygen is allowed to reach equilibrium in a container of volume 1800 cm3 at temperature T. At equilibrium, the mixture contains
November 2020, Paper 1, Q06.1 (1 mark): Draw a cross (x) on the appropriate axis of Figure 3 when the mixture reaches equilibrium. [1 mark]
November 2020, Paper 1, Q06.4 (2 marks): Some more carbon monoxide is added to the mixture in Question 06.2. The new mixture is allowed to reach equilibrium at temperature T. State the effect, if any,
November 2020, Paper 2, Q09.1 (2 marks): Calculate the amount of A and the amount of B, in moles, in the equilibrium mixture. [2 marks] Amount of A mol Amount of B mol
November 2020, Paper 2, Q09.2 (4 marks): At a different temperature, another equilibrium mixture contains 0.30 mol of A, 0.25 mol of B and 0.020 mol of C in 350 cm3 of solution. Calculate the value of
November 2020, Paper 2, Q09.3 (1 mark): Suggest why an expression for K can be written without the concentration of water. [1 mark]
November 2020, Paper 2, Q09.4 (5 marks): Distilled water is added to 4.71 g of chloroethanal (Mr = 78.5) to make 50.0 cm3 of solution. The mixture is allowed to reach equilibrium. The value of the equi
November 2020, AS Paper 1, Q19 (1 mark): Which statement is not always correct for a reaction at equilibrium? reactants ⇌ products [1 mark] A The concentrations of the reactants and products are equal.
November 2020, AS Paper 2, Q08.1 (2 marks): Give an expression for Kc for this equilibrium. State its units. [2 marks] Kc Units of Kc
November 2020, AS Paper 2, Q08.2 (3 marks): Table 4 shows the amount of each substance in an equilibrium mixture in a container of volume 750 cm3 Table 4 Substance C2H5OH(g) H2O(g) CO(g) H2(g) Amount of s
November 2020, AS Paper 2, Q08.3 (4 marks): The pressure of the equilibrium mixture was increased by reducing the volume of the container at constant temperature. Predict the effect of increasing the pres
June 2019, Paper 3, Q09 (1 mark): Which change leads to a higher concentration of SO3 in this equilibrium mixture? 2 SO2(g) + O2(g) ⇌ 2 SO3(g) ∆H = −188 kJ mol−1 [1 mark] A higher concentration
June 2019, AS Paper 1, Q05.1 (2 marks): 1.50 mol of NO are mixed with 1.00 mol of Cl2 and the mixture is left to reach equilibrium at a given temperature. The equilibrium mixture contains 0.350 mol of
June 2019, AS Paper 1, Q05.2 (1 mark): Give the expression for the equilibrium constant, Kc, for the reaction between nitrogen monoxide and chlorine to form nitrosyl chloride. [1 mark] Kc =
June 2019, AS Paper 1, Q05.3 (4 marks): A different equilibrium mixture is prepared in a flask of volume 800 cm3 at a different temperature. At equilibrium this mixture contains 0.850 mol of NO and 0.
June 2019, AS Paper 2, Q05.3 (6 marks): Methanol is made by the reaction of carbon monoxide with hydrogen. CO + 2 H2 ⇌ CH3OH ∆H = –91 kJ mol–1 The reaction uses a copper-based catalyst, a pressure of
June 2019, AS Paper 2, Q12 (1 mark): When one mole of ammonia is heated to a given temperature, 50 % of it dissociates and the following equilibrium is established. NH3(g) ⇌ 1 2 N2(g) + 3 2 H2(g) W
June 2018, Paper 2, Q04.1 (5 marks): A beaker contained 40 cm3 of a 0.16 mol dm–3 aqueous solution of A. 9.5 × 10–3 mol of B and 2.8 × 10–2 mol of C were added to the beaker and the mixture was lef
June 2018, Paper 2, Q04.2 (2 marks): Give the expression for the equilibrium constant (Kc) for this equilibrium and its units. [2 marks] Kc Units
June 2018, Paper 2, Q04.3 (3 marks): A different equilibrium mixture of these four compounds, at a different temperature, contained 0.21 mol of B, 1.05 mol of C and 0.076 mol of D in a total volume
June 2018, Paper 2, Q04.4 (3 marks): Justify the statement that adding more water to the equilibrium mixture in Question 04.3 will lower the amount of A in the mixture. [3 marks]
June 2018, Paper 3, Q34 (1 mark): For this reaction at equilibrium, which combination of temperature and pressure would give the greatest equilibrium yield of products? W(g) + X(g) ⇌ 2Y(g) + Z(g
June 2018, AS Paper 1, Q05.1 (2 marks): State the time, to the nearest minute, when equilibrium is first established. Explain your answer. [2 marks] Time minutes Explanation
June 2018, AS Paper 1, Q05.2 (2 marks): Sketch on the graph in Figure 4 how the concentration of sulfur dioxide changes over these 6 minutes at temperature T1 [2 marks]
June 2018, AS Paper 1, Q05.3 (2 marks): The temperature of the mixture was changed to T2 and the mixture left to establish a new equilibrium. In the new equilibrium mixture the concentration of sulfur
June 2018, AS Paper 2, Q08.1 (2 marks): State and explain the effect of using a catalyst on the yield of methanol in this equilibrium. [2 marks]
June 2018, AS Paper 2, Q08.2 (1 mark): Give an expression for the equilibrium constant (Kc) for this reaction. [1 mark]
June 2018, AS Paper 2, Q08.3 (3 marks): A mixture of carbon monoxide and hydrogen was allowed to reach equilibrium in a container of volume 250 cm3 at temperature T. At equilibrium, the mixture contai
June 2018, AS Paper 2, Q08.4 (2 marks): Methanol decomposes on heating in a reaction that is the reverse of that used in its manufacture. CH3OH(g) ⇌ CO(g) + 2H2(g) Use your answer from Question 08.3 t
June 2017, Paper 1, Q09.1 (6 marks): The first stage involves a gaseous equilibrium between the reactants (methane and steam), and some gaseous products. Figures 1 and 2 show the percentage convers
June 2017, Paper 2, Q05.2 (3 marks): A small amount of catalyst was added to a mixture of 0.470 mol of ethanoic acid and 0.205 mol of ethane-1,2-diol. The mixture was left to reach equilibrium at a
June 2017, Paper 2, Q05.3 (2 marks): Write an expression for the equilibrium constant, Kc, for the reaction. The total volume of the mixture does not need to be measured to allow a correct value fo
June 2017, Paper 2, Q05.4 (3 marks): A different mixture of ethanoic acid, ethane-1,2-diol and water was prepared and left to reach equilibrium at a different temperature from the experiment in Que
June 2017, Paper 3, Q20 (1 mark): An equilibrium mixture is prepared in a container of fixed volume. CO(g) + Cl2(g) ⇌ COCl2(g) ΔH = −108 kJ mol−1 The temperature of this mixture is decreased and
June 2017, AS Paper 1, Q04.1 (1 mark): The amount, in moles, of each of P and Q at equilibrium is (1− x). Deduce in terms of x the amount, in moles, of R in the equilibrium mixture. [1 mark
June 2017, AS Paper 1, Q04.2 (3 marks): At 298 K the value of the equilibrium constant Kc = 3.6 Calculate a value for the equilibrium concentration, in mol dm−3, of R. [3 marks Equilibrium concentrati
June 2017, AS Paper 1, Q19: The forward reaction in this equilibrium is endothermic COCl2 (g) ⇌ CO(g) + Cl2 (g) Which statement is correct? [1 mar A If the total pressure is increased at c
June 2017, AS Paper 2, Q21 (1 mark): Hydrogen can be produced by this reaction. CO(g) + H2O(g) ⇌ CO2(g) + H2(g) In an experiment 4.20 mol of carbon monoxide were mixed with 2.00 mol of steam. When
June 2016, AS Paper 1, Q19: A pale brown mixture of NO2 and N2O4 is allowed to reach equilibrium in a sealed gas syringe according to the following equation. 2NO2(g) ⇌ N2O4(g) When the plu
June 2016, AS Paper 2, Q01.1 (2 marks): Write an expression for the equilibrium constant Kc for this equilibrium. Deduce the units of Kc. [2 marks] Expression Units
June 2016, AS Paper 2, Q01.2 (2 marks): An equilibrium mixture was found to contain 0.700 mol of ethene, 1.20 mol of steam and 4.40 mol of ethanol at a temperature T. The volume of the container was 2
June 2016, AS Paper 2, Q19 (1 mark): A and B react together in this reversible reaction. A + 3B ⇌ C + 2D A mixture of 10 mol of A and 10 mol of B were left to reach equilibrium. The equilibrium mix
June 2016, AS Paper 2, Q21 (1 mark): Which of the following shows how the equilibrium yield of hydrogen and the value of the equilibrium constant are affected by the changes shown? [1 mark] Change
Specimen, Paper 1, Q04.4 (3 marks): Use Le Chatelier's principle to justify why the reaction is carried out at a high pressure rather than at atmospheric pressure. [3 marks] 0 4 . 4
Specimen, Paper 3, Q02.1 (6 marks): Kc = 6 A student obtained the titration results given in Table 2. Table 2 Rough 1 2 3 Final burette reading / cm3 4.60 8.65 12.85 16.80 Initial burette reading
Specimen, Paper 3, Q11: When one mole of ammonia is heated to a given temperature, 50% of the compound dissociates and the following equilibrium is established. NH3(g) 1 2N2(g) + 3 2H2

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