Equilibrium constant Kc for homogeneous systems: AQA A‑Level Chemistry questions

AQA A-Level Chemistry past-paper questions on 3.1.6.2 Equilibrium constant Kc for homogeneous systems, 2008–2025, with mark schemes and examiner’s reports where available.

All 106 questions on Equilibrium constant Kc for homogeneous systems, as a list

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, Q07.3 (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 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, 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 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, 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 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, 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
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, 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 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 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
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, 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, 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 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, 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 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 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 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 (1 mark): 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
June 2016, CHEM4 (old spec), Q2(c)(i) (2 marks): Calculate the amount, in moles, of ethanal and of ethanol in this equilibrium mixture. [2 marks] Amount of ethanal mol Amount of ethanol mol Space for working
June 2016, CHEM4 (old spec), Q2(c)(ii) (4 marks): In a different experiment using the same reaction as in part (c), an equilibrium mixture was established at a given temperature. This mixture contained 0.58 mol
June 2015, CHEM4 (old spec), Q2(a) (2 marks): Write an expression for the equilibrium constant, Kc, for this reaction and deduce its units. [2 marks] Kc Units
June 2015, CHEM4 (old spec), Q2(b) (3 marks): Samples of sulfur dioxide, oxygen and sulfur trioxide were added to a flask of volume 1.40 dm3 and allowed to reach equilibrium at a given temperature. The flas
June 2015, CHEM4 (old spec), Q2(c)(i) (1 mark): State the effect, if any, of using a smaller flask on the value of Kc [1 mark]
June 2014, CHEM4 (old spec), Q1(a) (2 marks): A 2.0 mol sample of E was heated in a sealed container with a 1.0 mol sample of F. Equilibrium was established at a given temperature and the equilibrium mixtur
June 2014, CHEM4 (old spec), Q1(b) (2 marks): Write an expression for the equilibrium constant Kc for this equilibrium. State the units of Kc [2 marks] Expression Units
June 2014, CHEM4 (old spec), Q1(c) (2 marks): A different mixture of E and F reached equilibrium at temperature T1 in a container of volume 1.50 dm3. This equilibrium mixture contained 2.50 mol of E, 1.20 m
June 2014, CHEM4 (old spec), Q1(e) (3 marks): The mixture in Question 1 (c) was allowed to reach equilibrium at temperature T2 in the original container of volume 1.50 dm3. The value of Kc for the equilibri
June 2013, CHEM4 (old spec), Q2(a) (2 marks): A 2.50 mol sample of NOCl was heated in a sealed container and equilibrium was established at a given temperature. The equilibrium mixture formed contained 0.80
June 2013, CHEM4 (old spec), Q2(b)(i) (1 mark): Write an expression for the equilibrium constant Kc (1 mark)
June 2013, CHEM4 (old spec), Q2(b)(ii) (4 marks): Calculate the amount, in moles, of Cl2 in this equilibrium mixture.
June 2013, CHEM4 (old spec), Q2(b)(iii) (2 marks): Consider this alternative equation for the equilibrium at temperature T. NOCl(g) NO(g) + – Cl2(g) Calculate a value for the different equilibrium constant Kc fo
January 2013, CHEM4 (old spec), Q3(b)(i) (3 marks): A mixture of 2.50 mol of A and 10.0 mol of ethanol was left to reach equilibrium in an inert solvent in the presence of a small amount of concentrated sulfuric
January 2013, CHEM4 (old spec), Q3(b)(iii) (1 mark): Using A to represent the acid and DEM to represent the ester, write an expression for the equilibrium constant Kc for the reaction. (1 mark)
January 2013, CHEM4 (old spec), Q3(b)(iv) (3 marks): In a second experiment, the equilibrium mixture was found to contain 0.85 mol of A, 7.2 mol of ethanol, 2.1 mol of DEM and 3.4 mol of water. Calculate a value o
June 2012, CHEM4 (old spec), Q1(a)(i) (2 marks): Calculate the amounts, in moles, of hydrogen and of iodine in the equilibrium mixture. Moles of hydrogen Moles of iodine (2 marks)
June 2012, CHEM4 (old spec), Q1(a)(ii) (1 mark): Write an expression for the equilibrium constant (Kc) for this equilibrium. (1 mark)
June 2012, CHEM4 (old spec), Q1(a)(iii) (1 mark): Kc for this equilibrium has no units. State why the units cancel in the expression for Kc (1 mark)
June 2012, CHEM4 (old spec), Q1(a)(iv) (2 marks): A different mixture of hydrogen, iodine and hydrogen iodide was left to reach equilibrium at the same temperature in a container of the same volume. This second
June 2012, CHEM4 (old spec), Q1(b)(i) (1 mark): Change: increase the temperature of the equilibrium mixture at constant pressure. H2(g) + l2(g) 2Hl(g) ΔH = +52 kJ mol–1 (1 mark)
June 2012, CHEM4 (old spec), Q1(b)(ii) (1 mark): Change: increase the total pressure of the equilibrium mixture at constant temperature. 3H2(g) + N2(g) 2NH3(g) ΔH = –92 kJ mol–1 (1 mark)
June 2012, CHEM4 (old spec), Q1(b)(iii) (1 mark): Change: add a catalyst to the equilibrium mixture at constant temperature. CO(g) + H2O(g) CO2(g) + H2(g) ΔH = – 41 kJ mol–1 (1 mark)
June 2012, CHEM4 (old spec), Q1(b)(iv) (1 mark): Change: add chlorine to the equilibrium mixture at constant temperature. PCl5(g) PCl3(g) + Cl2(g) ΔH = +93 kJ mol–1 (1 mark)
January 2012, CHEM4 (old spec), Q2(a)(i) (2 marks): Calculate the amount, in moles, of sulfur trioxide and of sulfur dioxide in the equilibrium mixture. Amount of sulfur trioxide Amount of sulfur dioxide (2 marks
January 2012, CHEM4 (old spec), Q2(a)(ii) (1 mark): Write an expression for the equilibrium constant, Kc, for this equilibrium. (1 mark)
January 2012, CHEM4 (old spec), Q2(a)(iii) (1 mark): Deduce the units of Kc for this equilibrium. (1 mark)
January 2012, CHEM4 (old spec), Q2(a)(iv) (3 marks): Calculate a value of Kc for this equilibrium at temperature T1 (If you were unable to complete the calculations in part (a) (i) you should assume that the amoun
January 2012, CHEM4 (old spec), Q2(b)(ii) (1 mark): the value of Kc (1 mark)
January 2012, CHEM4 (old spec), Q2(c) (3 marks): The experiment was repeated in the original container but at temperature T2 The value of Kc was smaller than the value at temperature T1 State which is the high
June 2011, CHEM4 (old spec), Q3(b) (1 mark): Write an expression for Kc for this reaction. (1 mark) 3
June 2011, CHEM4 (old spec), Q3(c) (4 marks): The volume of the container was 10.0 dm3. Calculate the concentration, in mol dm–3, of Q in the equilibrium mixture.
June 2011, CHEM4 (old spec), Q3(f) (1 mark): State the effect, if any, on the value of Kc of increasing the temperature. All other factors are unchanged. (1 mark)
June 2011, CHEM4 (old spec), Q3(g) (1 mark): State the effect, if any, on the value of Kc of using a container of larger volume. All other factors are unchanged. (1 mark)
June 2011, CHEM4 (old spec), Q3(h) (1 mark): Deduce the value of the equilibrium constant, at temperature T, for the reaction 2R(g) P(g) + 2Q(g) (1 mark)
January 2011, CHEM4 (old spec), Q3(a) (2 marks): A sample of synthesis gas containing 0.240 mol of carbon monoxide and 0.380 mol of hydrogen was sealed together with a catalyst in a container of volume 1.50 dm
January 2011, CHEM4 (old spec), Q3(b)(i) (1 mark): Write an expression for the equilibrium constant Kc for this reaction. (1 mark)
January 2011, CHEM4 (old spec), Q3(b)(ii) (4 marks): Calculate a value for Kc for the reaction at temperature T1 and state its units. Calculation
January 2011, CHEM4 (old spec), Q3(b)(iii) (1 mark): State the effect, if any, on the value of Kc of adding more hydrogen to the equilibrium mixture. (1 mark)
June 2010, CHEM4 (old spec), Q2(a)(i) (3 marks): Calculate the amounts, in moles, of methane, steam and hydrogen in the equilibrium mixture. Moles of methane Moles of steam Moles of hydrogen (3 marks) 3 3
June 2010, CHEM4 (old spec), Q2(a)(ii) (1 mark): The volume of the flask was 5.0dm3. Calculate the concentration, in moldm–3, of methane in the equilibrium mixture. (1 mark)
June 2010, CHEM4 (old spec), Q2(b)(i) (1 mark): Write an expression for the equilibrium constant, Kc, for this reaction. (1 mark)
June 2010, CHEM4 (old spec), Q2(b)(ii) (3 marks): Calculate a value for Kc at temperature T and give its units. Calculation
January 2010, CHEM4 (old spec), Q1(a)(i) (3 marks): Calculate the amounts, in moles, of propanoic acid, of ethanol and of water in this equilibrium mixture. Moles of propanoic acid Moles of ethanol Moles of water
January 2010, CHEM4 (old spec), Q1(a)(ii) (1 mark): Write an expression for the equilibrium constant, Kc, for this equilibrium. (1 mark)
January 2010, CHEM4 (old spec), Q1(a)(iii) (3 marks): Calculate a value for Kc for this equilibrium at this temperature. Explain why this Kc value has no units. Calculation
January 2010, CHEM4 (old spec), Q1(b)(iii) (1 mark): the value of Kc (1 mark)
June 2008, CHM5 (2008 spec), Q9(b) (7 marks): 9 (b) Methanol can be produced by using a reversible reaction between carbon monoxide and hydrogen. 2H2(g) + CO(g) CH3OH(g) When 2.00 mol of hydrogen and 1.00mo
January 2008, CHM4 (2008 spec), Q3(a) (1 mark): (a) Write an expression for the equilibrium constant, Kc, for this reaction. (1 mark)
January 2008, CHM4 (2008 spec), Q3(b) (4 marks): (b) At a given temperature and pressure, the equilibrium mixture contained 0.44 mol of methane, 0.28 mol of hydrogen and 0.12 mol of ethyne (C2H2) in a containe
January 2008, CHM4 (2008 spec), Q3(c) (2 marks): (c) State the effect of an increase in temperature on the position of this equilibrium and on the value of Kc for this reaction. Effect on position of equilibri
January 2008, CHM4 (2008 spec), Q3(d) (2 marks): (d) State the effect of an increase in pressure on the position of this equilibrium and on the value of Kc for this reaction. Effect on position of equilibrium
January 2008, CHM4 (2008 spec), Q3(g) (2 marks): (g) A different equilibrium mixture was produced starting from methane alone. 2CH4(g) 3H2(g) + C2H2(g) When 3.0 mol of methane were used, the equilibrium mixtur

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