Entropy: Edexcel International A Level Chemistry questions

Every Edexcel International A Level Chemistry exam question on 12A Entropy (specification points 12.1–12.11), 2019–2025, with its mark scheme and examiner’s report.

All 87 questions on Entropy, as a list

June 2025, Unit 4, Q3 (1 mark): Which of these substances would be expected to have the greatest standard molar entropy? A FeO B FeS C FeCl2 D FeCl3
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, Q19(a)(ii) (2 marks): Using the data in the table, calculate the standard molar entropy change, ΔSd system , for this reaction. (2)
June 2025, Unit 4, Q19(a)(iii) (3 marks): Using your answers from (a)(i) and (a)(ii), calculate the lowest temperature at which hydrated copper(II) sulfate will decompose. (3)
June 2025, Unit 5, Q15(d)(ii) (2 marks): Explain, by considering the equation shown, why this process is thermodynamically feasible. Pt(Cl)2(NH3)2 + DNA → [Pt(NH3)2(DNA)] 2+ + 2Cl − (2)
June 2025 (A), Unit 5, Q8 (1 mark): When EDTA4– is added to an aqueous solution of iron(III) ions, the EDTA complex is formed. Which is the best explanation for this? A iron(III) ions form stronge
January 2025, Unit 4, Q9 (1 mark): Which pair of values will always give a thermodynamically feasible reaction? Entropy change of the system Enthalpy change of reaction A negative positive B nega
January 2025, Unit 4, Q14 (1 mark): Which has the greatest molar entropy? A Hg(l) B H2O(l) C NO(g) D NO2(g)
January 2025, Unit 4, Q19(a) (2 marks): Give two reasons why this reaction is thermodynamically feasible when considering the entropy of the system. (2)
January 2025, Unit 4, Q19(b) (3 marks): Describe, in terms of the particles involved, why the reaction does not occur until the tablets are dissolved in water. (3)
January 2025, Unit 4, Q19(c) (2 marks): For the reaction at 25°C, the standard entropy change of the surroundings, ∆Ssurroundings = −234.9 J K−1 mol−1 . Calculate the enthalpy change of the reaction.
October 2024, Unit 4, Q11 (1 mark): Some thermodynamic information is shown for four reactions, W, X, Y and Z, at 298 K. ΔH TΔSsystem Reaction negative and with a larger W negative negative value
October 2024, Unit 4, Q20(a)(i) (2 marks): Calculate the standard entropy change for the system, ∆Ssystem . Standard molar entropy Compound / J K–1 mol–1 BaCO3 112.1 BaO 70.4 CO2 213.6 (2)
October 2024, Unit 4, Q20(a)(ii) (3 marks): The lowest temperature at which barium carbonate, BaCO3 , decomposes is 712 °C. Use this information and your answer from (a)(i) to calculate the standard entha
October 2024, Unit 5, Q18(d)(i) (1 mark): Give a reason, by referring to the equation, why the formation of the diamine complex from the aqueous complex ion is thermodynamically favoured. (1)
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
June 2024, Unit 4, Q15(a)(ii) (2 marks): The entropy change of the system, ΔSsystem , for Reaction 1 is –43.8 J K–1 mol–1. Suggest, with reference to the equation, why ΔSsystem for this reaction is neg
June 2024, Unit 4, Q15(a)(iii) (2 marks): The enthalpy change, ΔH, for Reaction 1 is –370 kJ mol–1. Calculate the entropy change of the surroundings, ΔSsurroundings , in J K–1 mol–1, for Reaction 1 at 2
June 2024, Unit 4, Q15(a)(iv) (2 marks): Calculate the total entropy change, ΔStotal , for Reaction 1 at 23.0 °C. Give your answer to an appropriate number of significant figures, and in units of J K–1
June 2024, Unit 4, Q15(c)(i) (2 marks): Calculate the entropy change of the system, ΔSsystem , in J K–1 mol–1, for Reaction 2. (2)
June 2024, Unit 4, Q15(c)(ii) (1 mark): State why the entropy change of the surroundings for Reaction 2 is highly positive, in terms of the bond strengths of the reactants and products. (1)
June 2024, Unit 5, Q16(b)(ii) (2 marks): Explain, using a balanced equation, why the formation of the dimethyldithiocarbamate complex from an aqueous solution of nickel ions is thermodynamically feasib
January 2024, Unit 4, Q4 (1 mark): The equations for three reactions involving hydrogen are shown. N2(g) + 3H2(g) → 2NH3(g) J N2(g) + 2H2(g) → N2H4(l) K I2(s) + H2(g) → 2HI(g) L What is the order
January 2024, Unit 4, Q5 (1 mark): Methane reacts with steam to produce carbon dioxide and hydrogen. CH4(g) + 2H2O(g) → CO2(g) + 4H2(g) The standard molar entropies of the reactants and products
January 2024, Unit 4, Q6 (1 mark): What are the signs of the entropy changes at 373 K when water vapour condenses? H2O(g) → H2O(l) ΔSsystem ΔSsurroundings A positive positive B positive negative
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, Q16(a)(i) (3 marks): Calculate the standard entropy change of the system for this reaction. (3)
October 2023, Unit 4, Q16(a)(iii) (3 marks): Explain how your answers to (a)(i) and (a)(ii) show that this reaction is feasible at all temperatures. (3)
October 2023, Unit 4, Q16(b)(i) (4 marks): Calculate the temperature at which this reaction becomes feasible. (4)
October 2023, Unit 4, Q16(b)(ii) (1 mark): Suggest why aluminium is not extracted from its oxide using a blast furnace. (1)
October 2023, Unit 5, Q19(e) (2 marks): Ethanedioate ligands react with iron(II) ions in aqueous solution. 2− → [Fe(C2O4)2 (H2O)2]2− + 4H2O [Fe(H2O)6]2+ + 2C2O4 Explain, in terms of entropy, why this
June 2023, Unit 4, Q20(a)(i) (2 marks): Some standard molecular entropy data are shown. Standard molecular entropy S Substance / J K–1 mol–1 nitrogen, N2 192 oxygen, O2 205 nitrous oxide, N2O 220 Calc
June 2023, Unit 4, Q20(a)(ii) (2 marks): The standard enthalpy change of the forward reaction is –82 kJ mol–1. Calculate the entropy change of the surroundings at 2048 K. Include a sign and units in yo
June 2023, Unit 4, Q20(a)(iii) (1 mark): Calculate the total entropy change of the reaction at 2048 K. Include a sign and units in your answer. (1)
June 2023, Unit 4, Q20(c) (2 marks): Explain whether or not this reaction occurs at 2048 K by considering the values calculated in (a) and (b). (2)
January 2023, Unit 4, Q4 (1 mark): Which graph shows the entropy of a substance as it changes state from solid to liquid to gas? Graph 1 Graph 2 Entropy Entropy Temperature Temperature Graph 3 Gr
January 2023, Unit 4, Q5 (1 mark): Two flasks, P and Q, are connected by a tube fitted with a tap. P Q Flask P contains argon gas and flask Q is in vacuum. Assume argon behaves as an ideal gas an
January 2023, Unit 4, Q6 (1 mark): When hydrogen and oxygen are mixed in a flask, there is no reaction. When a platinum gauze is added to the flask, the mixture explodes. It can be deduced that,
January 2023, Unit 4, Q20(a)(i) (2 marks): Calculate the entropy change in the system, ΔS d system , for the cracking of butane. Include a sign and units with your answer. (2)
January 2023, Unit 4, Q20(a)(iii) (2 marks): Calculate the entropy change in the surroundings, ΔS d surroundings, at 298 K for the cracking of butane, using your answer to (a)(ii). Include a sign and units
January 2023, Unit 4, Q20(a)(iv) (1 mark): Calculate the total entropy change, ΔS d total, at 298 K for the cracking of butane, using your answers to (a)(i) and (a)(iii). Include a sign and units with yo
January 2023, Unit 4, Q20(a)(v) (2 marks): Calculate the temperature at which the cracking reaction becomes feasible. (2)
October 2022, Unit 4, Q5 (1 mark): Which sequence shows the elements in order of increasing standard entropy? A He(g) < O2(g) < Hg(l) < Os(s) B O2(g) < He(g) < Hg(l) < Os(s) C Os(s) < Hg(l) < He(
October 2022, Unit 4, Q17(a)(iii) (2 marks): Explain why the entropy change of the system, ΔSsystem , is greater for Reaction 1 than for Reaction 2. (2)
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
October 2022, Unit 4, Q18(c)(vi) (2 marks): The equation relating ∆G, ∆H and ∆Ssystem is shown. ∆G = ∆H − T∆Ssystem Calculate ∆Ssystem at 620 K , using your answers to (c)(iv) and (c)(v). (2)
October 2022, Unit 4, Q18(d) (3 marks): Explain, in terms of the total entropy change, ∆Stotal , why this reaction is feasible at any temperature. Assume that both ∆H and ∆Ssystem are independent of t
October 2022, Unit 5, Q23(e)(ii) (2 marks): Explain why the salen ligand complex of the Ni2+ ion is much more stable than the aqua complex of the same ion. (2)
June 2022, Unit 4, Q14 (1 mark): In which series does the standard molar entropy of the compounds increase? A CaO(s) < H2O(l) < CO2(g) < SO2(g) B CaO(s) < H2O(l) < SO2(g) < CO2(g) C SO2(g) < CO
June 2022, Unit 4, Q21(a)(ii) (3 marks): Calculate the entropy change, ∆Ssystem , for this reaction. (3)
June 2022, Unit 4, Q21(a)(iii) (3 marks): Calculate the temperature at which this reaction becomes feasible, using your answers from (a)(i) and (a)(ii). (3)
June 2022, Unit 4, Q21(b)(i) (2 marks): Explain why the reaction should be feasible at any temperature. (2)
June 2022, Unit 4, Q21(b)(ii) (3 marks): Explain how an increase in temperature would affect ∆Stotal of this reaction. No calculation is required. (3)
June 2022, Unit 5, Q15(d) (2 marks): The concentration of nickel(II) ions, Ni2+(aq), can be determined by forming a complex with the ligand dimethylglyoxime, C4H8N2O2 . [Ni(H2O)6]2+ + 2C4H8N2O2 + 2
January 2022, Unit 4, Q22(a) (2 marks): At 298 K the standard entropy change of the system, ΔS d system = –98 J K–1 mol–1. Calculate the standard entropy of one mole of ammonia. Use the value of ΔS d
January 2022, Unit 4, Q22(b) (2 marks): The value of the total entropy change, ΔS total, varies with temperature. Data for the value of ΔS total at different temperatures but at standard pressure of 1
January 2022, Unit 4, Q22(c)(i) (1 mark): Determine the gradient of the line plotted in (b), including units in your answer. (1)
January 2022, Unit 4, Q22(c)(ii) (1 mark): Identify the thermodynamic quantity that can be obtained from this gradient. (1)
January 2022, Unit 4, Q22(c)(iii) (1 mark): Determine the temperature at which the reaction ceases to be thermodynamically feasible at a pressure of 100 kPa. (1)
January 2022, Unit 4, Q22(d)(i) (1 mark): State the relationship between the total entropy, ΔS total, and the equilibrium constant, K. (1)
January 2022, Unit 4, Q22(d)(ii) (2 marks): Calculate the value of the equilibrium constant K at 750 K. [ΔS total at 750 K = –37.7 J K–1 mol–1] (2)
January 2022, Unit 4, Q22(d)(iii) (3 marks): Explain why ΔS total decreases with an increase in temperature. (3)
October 2021, Unit 4, Q3 (1 mark): Ammonium nitrate is very soluble in water. −(aq) ∆H = +25.8 kJ mol−1 NH4NO3(s) + aq → NH4 +(aq) + NO3 What is the best explanation for this? A all ammonium salt
October 2021, Unit 4, Q4 (1 mark): The decomposition of calcium carbonate is an important reaction in the manufacture of cement. CaCO3(s) → CaO(s) + CO2(g) ∆H = +178 kJ mol−1 What are the signs o
October 2021, Unit 4, Q5 (1 mark): The standard molar entropy, S , of a substance A is not affected by changes of state or changes in temperature B only changes when the temperature changes C onl
October 2021, Unit 5, Q7 (1 mark): Some nickel(II) complex ions are formed by the addition of complexing agents to nickel(II) ions, [Ni(H2O)6]2+ , in aqueous solution. On formation, which of thes
June 2021, Unit 4, Q1 (1 mark): Which of these gases would have the greatest standard molar entropy? A NH3 B H2 C N2 D SO2
June 2021, Unit 4, Q2 (1 mark): What is the standard entropy change of the system, in J K–1 mol–1, for the reaction between nitrogen and hydrogen to form ammonia? N2 + 3H2 → 2NH3 Standard mola
June 2021, Unit 4, Q15(a) (2 marks): Calculate the value for the standard entropy change in the surroundings, ∆Ssurroundings , when ammonium nitrate dissolves in water at 298 K. Include a sign and
June 2021, Unit 4, Q15(b) (3 marks): Explain what can be deduced from your answer in (a) about the sign and the value of the standard entropy change in the system, ∆Ssystem , when NH4NO3 dissolves.
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)
June 2021, Unit 4, Q20(c) (3 marks): Draw a sketch of entropy against temperature for water to illustrate the entropy changes as temperature increases, including when water changes state. A scale i
January 2021, Unit 4, Q1 (1 mark): Which of these has the highest standard molar entropy at 298 K and 1 atm pressure? A carbon dioxide, CO2 B copper, Cu C ethanol, C2H5OH D hydrogen, H2
January 2021, Unit 4, Q2 (1 mark): The entropy change of the surroundings, ¨Ssurroundings , and the entropy change of the system, ¨Ssystem , for four different reactions are given. ¨Ssurroundings
January 2021, Unit 4, Q5 (1 mark): The standard enthalpy change of solution of potassium chloride, KCl, is +17 kJ mol−1. The solubility of potassium chloride in water at 298 K is 359 g dm−3. Whic
January 2021, Unit 4, Q6 (1 mark): The total entropy change, ¨Stotal , of a reaction at 298 K is −85.0 J K−1 mol−1. What is the value of the equilibrium constant for this reaction at 298 K? [R =
January 2021, Unit 4, Q20(a) (5 marks): Potassium bromate(V) decomposes to form potassium bromide and oxygen. 2KBrO3(s) o 2KBr(s) + 3O2(g) ¨rH = −67.2 kJ mol−1 The standard molar entropies of these su
October 2020, Unit 4, Q6 (1 mark): The equation for an exothermic reaction is shown. Mg(s) + 2HCl(aq) → MgCl2(aq) + H2(g) Which of these is true? A ΔH is positive B ΔSsurroundings is positive C Δ
October 2020, Unit 4, Q19(a)(i) (2 marks): Calculate ∆Ssystem for this reaction at 298 K. Include a sign and units with your answer. [Standard molar entropy, S , for 1 mol of each gas, in J K−1 mol−1 : N
October 2020, Unit 4, Q19(a)(ii) (2 marks): Explain, using ideas about disorder, whether the sign of your answer to (a)(i) is as expected. (2)
October 2020, Unit 4, Q19(a)(iii) (2 marks): At 700 K, the enthalpy change for this reaction is ∆H = −110.2 kJ mol−1. Calculate the entropy change of the surroundings, ∆Ssurroundings , at 700 K. Include a
October 2020, Unit 4, Q19(a)(iv) (1 mark): At 700 K, the total entropy change, ∆Stotal = −78.7 J K−1 mol−1. Calculate ∆Ssystem for this reaction at 700 K. Include a sign and units in your answer. (1)
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
January 2020, Unit 4, Q7 (1 mark): Which of these changes has the largest increase in the entropy of the system? A H2O(s) → H2O(l) B Hg(l) → Hg(g) C H2O(l) + HCl(g) → H3O+(aq) + Cl–(aq) D C(graph
January 2020, Unit 4, Q19(a)(i) (5 marks): Calculate the total entropy change, ¨Stotal, for this reaction, at 298 K, using the information given. Include a sign and units in your answer which should be g
January 2020, Unit 4, Q19(a)(ii) (3 marks): In industry, the reaction is carried out at 700 °C. By considering entropy and other relevant factors, justify the use of this temperature. (3)
January 2020, Unit 4, Q19(a)(iii) (2 marks): Use your answer from (a)(i) to calculate the equilibrium constant for the reaction at 298 K. (2)

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