Chemical equilibria: Edexcel International A Level Chemistry questions

Every Edexcel International A Level Chemistry exam question on Chemical equilibria (specification points 13.1–13.9), 2019–2025, with its mark scheme and examiner’s report.

All 79 questions on Chemical equilibria, as a list

June 2025, Unit 4, Q13(a) (1 mark): Which is the expression for the equilibrium constant, Kp? (1) 2 p SO 3 A Kp = 2 p SO p O 2 2 2 SO 3 B Kp = 2 SO O 2 2 2 p SO 3 C Kp = 2 p SO p O 2 2 2 p SO p
June 2025, Unit 4, Q13(b) (1 mark): Which statement about this equilibrium is correct? (1) A increasing the pressure increases the value of Kp B decreasing the pressure decreases the equilibrium y
June 2025, Unit 4, Q13(c) (1 mark): What is the relationship between the equilibrium constant, K, and ΔStotal ? (1) A ΔStotal = R ln K ln ΔStotal = R K B C ΔStotal = R log K D log ΔStotal = R K
June 2025, Unit 4, Q14(a) (2 marks): A mixture of nitrosyl chloride, chlorine and nitric oxide was placed in a sealed container and allowed to reach equilibrium. Explain what you would expect to se
June 2025, Unit 4, Q14(b)(i) (1 mark): Write the expression for the equilibrium constant Kc . (1)
June 2025, Unit 4, Q14(b)(ii) (2 marks): Complete the table using the equilibrium equation and the data. (2) Substance NOCl NO Cl2 Initial mol 0.250 0 0 Equilibrium mol 0.016 Concentration / mol dm3
June 2025, Unit 4, Q14(b)(iii) (3 marks): Using your answers from (b)(i) and (b)(ii), calculate the equilibrium constant, Kc . Give your answer to an appropriate number of significant figures and includ
June 2025, Unit 4, Q14(b)(iv) (2 marks): When the temperature is reduced, the value of the equilibrium constant, Kc , becomes smaller. Explain what can be deduced about the nature of the reaction. (2)
June 2025, Unit 6, Q2(a) (1 mark): Give the reason why the conical flask is left for one day at the end of Step 2. (1)
June 2025, Unit 6, Q2(c)(iii) (1 mark): The solubility of calcium hydroxide decreases with increasing temperature. Suggest why the mean titre from the experiment in (c)(i) does not agree with the expe
June 2025, Unit 6, Q2(d) (2 marks): From the results of the experiment, the student determined the concentration of the saturated solution of calcium hydroxide to be 0.0190 mol dm–3. Calculate the
January 2025, Unit 4, Q5(a) (1 mark): What is the numerical value of Kp at 25°C using Equation 2? (1) A 2.0 × 1012 B 2.0 × 1022 C 2.0 × 1024 D 4.0 × 1024
January 2025, Unit 4, Q5(b) (1 mark): The relationship between Kp and Kc is shown. K p K c Δ n R T where T is the temperature in kelvin, R is the gas constant 0.082 dm3 atm mol–1 K–1 and ∆n = moles
January 2025, Unit 4, Q10(a) (1 mark): The equation for the reaction between hydrogen and iodine is shown. H2(g) + I2(g)  2HI(g) What is the effect, if any, of an increase in pressure on the appeara
January 2025, Unit 4, Q10(b) (1 mark): The equation for the manufacture of ammonia by the Haber process is shown. N2(g) + 3H2(g)  2NH3(g) ∆H = –92.2 kJ mol–1 (1) Kp = 6.76 × 105 atm–2 at 298 K Which
January 2025, Unit 4, Q10(c) (1 mark): The equation for the equilibrium between nitrogen dioxide and dinitrogen tetroxide is shown. N2O4(g)  2NO2(g) A change in conditions results in Kp increasing f
October 2024, Unit 4, Q9 (1 mark): Magnesium nitrate decomposes on heating as shown. Mg(NO3)2(s)  MgO(s) + 2NO2(g) + ½O2(g) What is the expression for the equilibrium constant, Kp , for this rea
June 2024, Unit 4, Q4(a) (1 mark): 10 mol of N2(g) is heated with 30 mol of H2(g) in a sealed container. At equilibrium, 8.0 mol of NH3(g) is present. What is the total amount of gas, in mol, in
June 2024, Unit 4, Q4(b) (1 mark): What is the expression for the equilibrium constant, Kp , for this reaction? (1) p ( N ) + p ( H ) 3 A 2 2 2 p ( NH ) 3 p ( NH ) 2 B 3 + 3 p ( N ) p ( H ) 2 2 p
June 2024, Unit 4, Q4(c) (1 mark): Which change would increase the value of Kp for this reaction? (1) A decreasing the temperature B decreasing the particle size of the catalyst C increasing the
June 2024, Unit 4, Q5 (1 mark): For all chemical reactions, the equilibrium constant, K, is related to the total entropy change, ΔStotal , by the expression shown. ΔStotal = R ln K ΔStotal for
January 2024, Unit 4, Q1(b) (1 mark): What are the units of the equilibrium constant, Kp, for this reaction? (1) A atm B atm–1 C atm4 D atm–4
January 2024, Unit 4, Q3(b) (1 mark): Which conditions favour the highest percentage of ammonia in an equilibrium mixture from identical amounts of nitrogen and hydrogen? (1) A a temperature of 400
January 2024, Unit 4, Q19(a)(i) (4 marks): Calculate the value for Kc for this equilibrium at 25 °C. Give your answer to an appropriate number of significant figures. (4)
January 2024, Unit 4, Q19(a)(iii) (3 marks): Deduce the effect of increasing the temperature on the total entropy change of this reaction, ΔStotal, and on the value of the equilibrium constant, Kc. Assume
October 2023, Unit 4, Q6 (1 mark): Heating copper(II) nitrate results in the equilibrium shown. 2Cu(NO3)2(s)  2CuO(s) + 4NO2(g) + O2(g) Which is the expression for Kp? × × A Kp = 2( CuO) p 4( NO
October 2023, Unit 4, Q15(a)(i) (3 marks): Calculate the number of moles of each substance at equilibrium. (3)
October 2023, Unit 4, Q15(a)(ii) (4 marks): Calculate the value of Kc under these conditions. Include units in your answer. (4)
June 2023, Unit 4, Q1 (1 mark): A homogeneous equilibrium is shown. W + X  2Y + Z What is the Kc expression for this equilibrium? A Kc = 2 Y Z W X 2 B Kc = Y Z W X C Kc = W X 2 Y Z D Kc = W X
June 2023, Unit 4, Q2 (1 mark): The reaction shown occurs at 360 °C and 1 atm. CO + H2O  CO2 + H2 ΔH = –41.2 kJ mol–1 What is the type of equilibrium and how is Kc affected by an increase in
June 2023, Unit 4, Q3 (1 mark): What are the units of Kp for the equilibrium shown? N2(g) + 3H2(g)  2NH3(g) A atm–1 B atm C atm–2 D atm2
June 2023, Unit 4, Q18(b) (2 marks): The equilibrium constant, Kp , for the reaction at 298 K is 1.55 × 106 atm–½. State what this value of the equilibrium constant indicates about the position of
January 2023, Unit 4, Q9(a) (1 mark): What is the equilibrium constant expression for this reaction? (1) × 4 A Kc = [ Fe O ] [ H ] 3 4 2 [ Fe] 3 × [ H O ] 4 2 × 4 B Kc = [ Fe O ] [ H ] 3 4 2 [ H O ]
January 2023, Unit 4, Q9(b) (1 mark): What is the effect on the equilibrium constant for this reaction if small pieces of iron are replaced by iron powder and if the temperature is increased? (1) Ir
January 2023, Unit 4, Q20(b)(i) (1 mark): Give the expression for the equilibrium constant, Kp, for this reaction. (1)
January 2023, Unit 4, Q20(b)(ii) (5 marks): Calculate the value of Kp, including units if required. (5)
October 2022, Unit 4, Q6(a) (1 mark): Which conditions of temperature and pressure would be expected to give the greatest equilibrium yield of NO? (1) A high temperature and high pressure B high tem
October 2022, Unit 4, Q6(c) (1 mark): What are the units of the equilibrium constant, Kp , for this reaction? (1) A atm−1 B atm C dm3 mol−1 D mol dm−3 Use this space for any rough working. Anything
October 2022, Unit 4, Q18(a) (1 mark): Write the expression for the equilibrium constant, Kc , of this system. (1)
October 2022, Unit 4, Q18(b) (4 marks): Chemist A carried out an experiment to determine Kc . 0.00500 mol of H2 and 0.0100 mol of I2 were heated in a sealed container of volume 1.00 dm3 . At equilibri
October 2022, Unit 4, Q18(c)(i) (2 marks): Complete the table of data. (2)
October 2022, Unit 4, Q18(c)(ii) (3 marks): Plot a graph of ln Kc against 1 / T. Include a line of best fit. (3) ln Kc 1 / T (K–1)
October 2022, Unit 4, Q18(c)(iii) (1 mark): Determine the gradient of your graph. You must show your working on the graph. (1)
October 2022, Unit 4, Q18(c)(iv) (2 marks): The gradient of the graph from (c)(iii) is related to the enthalpy change of the reaction, ∆H . gradient = Δ H − R Calculate ∆H , in J mol−1 , using your value
October 2022, Unit 4, Q18(c)(v) (2 marks): The free energy change for the reaction, ∆G , is related to entropy and can be calculated from Kc . ∆G = −RT ln Kc Calculate ∆G at 620 K , using this equation a
June 2022, Unit 4, Q13 (1 mark): Solid vanadium(V) oxide catalyses the equilibrium shown. 2SO2(g) + O2(g)  2SO3(g) ∆H = −196 kJ mol−1 Which statement is correct? A vanadium(V) oxide is a homog
June 2022, Unit 4, Q16(a)(i) (1 mark): Write the expression for the equilibrium constant, Kp . (1)
June 2022, Unit 4, Q16(a)(ii) (3 marks): An equilibrium was established by mixing nitrogen and hydrogen in a 1 : 3 ratio by volume, at a temperature of 450 °C and pressure of 200 atm. The equilibrium m
June 2022, Unit 4, Q16(a)(iii) (3 marks): Calculate the equilibrium constant. Give your answer to an appropriate number of significant figures and include units, if required. (3)
June 2022, Unit 4, Q16(a)(iv) (2 marks): When the temperature was reduced to 400 °C at the same pressure, the equilibrium mixture contained 36 % of ammonia. Explain what can be deduced about this react
January 2022, Unit 4, Q3(a) (1 mark): Which will increase when the temperature is lowered? (1) A the mole fraction of carbon dioxide B the partial pressure of carbon monoxide C the rate of the backw
January 2022, Unit 4, Q3(b) (1 mark): At 680 °C and 1 atm, 52.6 % of the molecules in the gas mixture are carbon monoxide. What is the partial pressure of carbon dioxide, in atmospheres? (1) A 0.237
January 2022, Unit 4, Q4 (1 mark): The equation for the precipitation of lead(II) chloride is shown. Pb2+(aq) + 2Cl–(aq)  PbCl2(s) What are the units of the equilibrium constant, Kc? A dm9 mol–3
January 2022, Unit 4, Q21(a)(i) (4 marks): Calculate the value of the equilibrium constant, Kc, for this reaction at 25 °C. (4)
January 2022, Unit 4, Q22(d)(iv) (1 mark): State how the Haber Process is made economically feasible at 750 K even though the total entropy change is negative. (1)
October 2021, Unit 4, Q6(a) (1 mark): What is the equilibrium constant, Kc , for this reaction? (1) B Kc = [ CO H ][ ] 2 A Kc = [CO][H2] [ ] C C Kc = [ CO H ][ ] D Kc = [ CO H ][ ] 2 2 [ H O ] [ H O
October 2021, Unit 4, Q6(b) (1 mark): What happens to the equilibrium constants of the forward and reverse reactions when the temperature is increased? (1) Kc of forward reaction Kc of reverse react
October 2021, Unit 4, Q19(a)(i) (1 mark): Give the expression for the equilibrium constant, Kp , for the reaction. (1)
October 2021, Unit 4, Q19(a)(ii) (5 marks): Calculate the equilibrium constant, Kp , for the hydration of ethene at 150 °C. Include units with your answer. (5)
October 2021, Unit 4, Q19(b) (3 marks): The manufacture of ethanol is carried out at 230 °C and 70 atm; the overall conversion into ethanol is 95 % . Comment on these conditions in relation to their e
June 2021, Unit 4, Q20(a)(i) (3 marks): An increase in the total pressure (3)
June 2021, Unit 4, Q20(a)(ii) (2 marks): An increase in the temperature (2)
June 2021, Unit 4, Q20(a)(iii) (2 marks): The use of a catalyst (2)
June 2021, Unit 4, Q20(b)(i) (3 marks): Complete the table. (3) Initial amount Equilibrium amount Mole fraction Substance / mol / mol at equilibrium HCl 0.850 O2 0.600 H2O 0 Cl2 0 0.250 0.189 Total mo
June 2021, Unit 4, Q20(b)(ii) (1 mark): Write the expression for the equilibrium constant, Kp . (1)
June 2021, Unit 4, Q20(b)(iii) (3 marks): Use your answers to (b)(i) and (b)(ii) to calculate the value for Kp . Give your answer to an appropriate number of significant figures, and include units. (3)
June 2021, Unit 4, Q20(b)(iv) (2 marks): Use your answer to (b)(iii) to calculate a value for the total entropy change of the reaction, ΔStotal . (2)
January 2021, Unit 4, Q18(a)(i) (1 mark): A catalyst of vanadium(V) oxide is used in this reaction. State the effect, if any, of the catalyst on the value of the equilibrium constant, Kp . (1)
January 2021, Unit 4, Q18(a)(ii) (2 marks): The temperature used for this reaction in industry is 700 K. Explain, in terms of the equilibrium constant and the equilibrium position, the effect of an increa
January 2021, Unit 4, Q18(a)(iii) (1 mark): Write the expression for the equilibrium constant, Kp , for this equilibrium. State symbols are not required. (1)
January 2021, Unit 4, Q18(a)(iv) (4 marks): A mixture of 2.00 mol of sulfur dioxide and 1.00 mol of oxygen is allowed to reach equilibrium at 5.00 atm pressure. 1.60 mol of sulfur trioxide is formed. Calc
October 2020, Unit 4, Q7 (1 mark): The equation for the equilibrium decomposition of hydrogen iodide into hydrogen and iodine can be written in two ways. 2HI(g)  H2(g) + I2(g) Equilibrium consta
October 2020, Unit 4, Q19(a)(v) (6 marks): Explain one advantage and one disadvantage of using a temperature higher than 700 K in the Haber process. Consider the effect of an increase in temperature on t
October 2020, Unit 4, Q19(b)(i) (1 mark): Write the expression for the equilibrium constant, Kp , for the reaction in the Haber Process. N2(g) + 3H2(g)  2NH3(g) (1)
October 2020, Unit 4, Q19(b)(ii) (3 marks): A mixture of nitrogen, hydrogen and ammonia is at equilibrium at 255 atm and 700 K. The partial pressure of nitrogen is 25 atm and that of hydrogen is 150 atm.
October 2020, Unit 4, Q19(b)(iii) (3 marks): The pressure of the system is doubled at constant temperature. Explain the effect of this on the yield of ammonia by considering the change in the Kp expression
January 2020, Unit 4, Q8 (1 mark): Equal amounts of W and X are mixed and allowed to reach equilibrium. W + X U Y + Z The value of the equilibrium constant is Kc = 4.85. At equilibrium, the mixtu
January 2020, Unit 4, Q13(a) (1 mark): In which flask(s) was the equilibrium approached from the right-hand side of the equation? (1) A flask 1 only B flask 4 only C flasks 1 and 4 only D flasks 2 an
January 2020, Unit 4, Q13(b) (1 mark): Which of these statements explains why it is possible to titrate the reaction mixture directly to find the equilibrium concentrations? (1) A the equilibrium rea

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