Enthalpy changes and Hess’s law: Edexcel International A Level Chemistry questions

Every Edexcel International A Level Chemistry exam question on Enthalpy changes and Hess’s law (specification points 6.1–6.8), 2019–2025, with its mark scheme and examiner’s report.

All 166 questions on Enthalpy changes and Hess’s law, as a list

June 2025, AS Unit 2, Q1(a) (1 mark): What is the expression for the enthalpy change of neutralisation of sodium hydroxide and ethanoic acid, in J mol–1? [Assume: the specific heat capacity of the m
June 2025, AS Unit 2, Q1(b) (1 mark): The measurement uncertainty in the thermometer used in the experiment is ±0.5 °C for each reading. What is the percentage uncertainty in the temperature change
June 2025, AS Unit 2, Q2(b) (1 mark): A data book value for the standard enthalpy change of combustion of methane is –890 kJ mol–1. What is the experimental value for the enthalpy change of vaporisa
June 2025, AS Unit 2, Q17(b)(i) (3 marks): Calculate ΔrH1 for Reaction 1. Include a sign and units in your answer. [Assume the specific heat capacity of the solution = 4.18 J g–1 °C–1 the density of the
June 2025, AS Unit 2, Q17(b)(ii) (3 marks): The enthalpy change of decomposition, ΔrH , of magnesium carbonate can be found using a Hess cycle. Calculate the enthalpy change of decomposition by using a co
June 2025, AS Unit 2, Q17(b)(iii) (1 mark): Give a reason why it is not possible to measure the enthalpy change for the decomposition directly. (1)
June 2025, AS Unit 3, Q5(b) (4 marks): The student carried out the reaction. The starting temperature recorded was 19.4°C. The maximum temperature recorded was 55.2°C. Calculate the value for the ent
June 2025, AS Unit 3, Q5(c) (1 mark): A second student repeated the experiment using the procedure described. The value obtained from this enthalpy change was considerably less exothermic than that
June 2025, AS Unit 3, Q5(d) (4 marks): Justify how the equipment and the procedure could be improved to give a more accurate value for the enthalpy change of the reaction. (4)
June 2025, Unit 4, Q19(a)(i) (2 marks): Using the data in the table, calculate the standard enthalpy change, ΔrHd, for this reaction. (2)
June 2025, Unit 4, Q19(b) (4 marks): Hydrated copper(II) sulfate is soluble in water. A student carried out an experiment to determine its enthalpy change of solution. 100 g of distilled water was
June 2025, Unit 5, Q16(a)(i) (1 mark): Complete the cycle by adding balancing numbers. (1) C(g) + H(g) C6H6(g) C(s) + H2(g) C6H6(l)
January 2025, AS Unit 2, Q21(b) (1 mark): A Hess cycle for the reaction is shown. –164.3 kJ mol–1 CH4(g) + ½O=O(g) CH3OH(l) –74.8 kJ mol–1 0.0 kJ mol–1 –239.1 kJ mol–1 C(s) + 2H2(g) + ½O2(g) State why t
October 2024, AS Unit 2, Q3 (1 mark): Which equation shows the reaction that occurs when the standard enthalpy change of formation of copper(II) carbonate is measured? A Cu(s) + C(s) + 3O(g) → CuCO3
October 2024, AS Unit 2, Q16(b)(i) (4 marks): In the first experiment, the student determined the enthalpy change when dissolving anhydrous magnesium sulfate. MgSO4(s) + (aq) → MgSO4(aq) 100.0 g of distille
October 2024, AS Unit 2, Q16(b)(ii) (2 marks): In the second experiment, the student determined the enthalpy change when dissolving hydrated magnesium sulfate. MgSO4·7H2O(s) + (aq) → MgSO4(aq) ∆H = +15.8 kJ
October 2024, AS Unit 2, Q16(b)(iii) (2 marks): Calculate the enthalpy change when anhydrous magnesium sulfate forms hydrated magnesium sulfate, using the completed Hess cycle and your answer in (b)(i). (2)
October 2024, AS Unit 3, Q2(a)(i) (3 marks): Draw two lines of best-fit to determine the maximum temperature change at the point of neutralisation. (3) Volume of hydrochloric acid at neutralisation cm3 Max
October 2024, AS Unit 3, Q2(a)(ii) (2 marks): Calculate the concentration of the sodium hydroxide solution, using an answer from (a)(i) and information from the procedure. (2)
October 2024, AS Unit 3, Q2(a)(iii) (4 marks): Calculate the enthalpy change of neutralisation, in kJ mol−1. (4) Assume the value of the specific heat capacity of the solution is 4.18 J g−1 °C−1 and the dens
October 2024, AS Unit 3, Q2(b) (2 marks): The published value for the enthalpy change of neutralisation is −55.84 kJ mol−1. The student’s value is significantly different from the published value. This
October 2024, Unit 4, Q20(b) (3 marks): Magnesium chloride, MgCl2(s), is used in the manufacture of tofu from soya milk. An experiment was carried out to determine the enthalpy change of solution, Δso
June 2024, AS Unit 2, Q1 (1 mark): An enthalpy level diagram for a reaction with an intermediate is shown. intermediate C B D Enthalpy A products reactants Progress of reaction Which arrow shows
June 2024, AS Unit 2, Q17(a) (3 marks): Find the end‑point volume and the maximum temperature by adding appropriate lines of best fit to the graph. (3) End‑point volume = Maximum temperature =
June 2024, AS Unit 2, Q17(b) (1 mark): Calculate the number of moles of ammonia added at the end‑point. (1)
June 2024, AS Unit 2, Q17(c) (5 marks): The reaction that occurs is shown. CH3COOH(aq) + NH3(aq) → CH3COONH4(aq) Calculate the enthalpy change of neutralisation for this reaction, in kJ mol‒1. Give yo
June 2024, AS Unit 3, Q4(b) (1 mark): State the purpose of measuring the temperature every 30 seconds for 2½ minutes in Step 2. (1)
June 2024, AS Unit 3, Q4(c) (2 marks): Explain why the temperature was not measured at 3 minutes. (2)
June 2024, AS Unit 3, Q4(d)(i) (2 marks): Determine the maximum temperature change, ∆T , for this reaction, using the graph. You must show your working on the graph. (2)
June 2024, AS Unit 3, Q4(d)(ii) (2 marks): Explain why the temperature decreases over time after 5 minutes. (2)
June 2024, AS Unit 3, Q4(d)(iv) (1 mark): State why the data will not result in the standard molar enthalpy change of neutralisation being calculated. (1)
June 2024, AS Unit 3, Q4(e)(i) (2 marks): Explain why it may or may not be valid to assume that the specific heat capacity of water is suitable to be used for this reaction. (2)
June 2024, AS Unit 3, Q4(e)(ii) (1 mark): State why the number of moles of sodium hydroxide and not the number of moles of sulfuric acid is used in the calculation for this experiment. (1)
June 2024 (R), AS Unit 2, Q2 (1 mark): The reaction profile for a reaction is shown. X Products W Enthalpy Y Z Reactants Progress of reaction Which arrow represents the activation energy of the forwa
June 2024 (R), AS Unit 2, Q6(a) (1 mark): Which is the correct expression to calculate the enthalpy change of neutralisation for this reaction, in J mol–1 ? (1) A Δ T 4.2 50 3 5.0 10 B Δ T 4.2 25 3 2.5
June 2024 (R), AS Unit 2, Q6(b) (1 mark): The table below shows the measurement uncertainty of some laboratory apparatus. Measurement uncertainty Apparatus on each reading / cm3 burette +/− 0.05 25 cm3
June 2024 (R), AS Unit 2, Q7 (1 mark): Which equation shows the reaction that occurs when the standard enthalpy change of atomisation of iodine is measured? A I2(s) → 2I(g) B ½I2(s) → I(g) C I2(g) →
June 2024 (R), AS Unit 2, Q18(b)(i) (2 marks): Complete the Hess cycle with two arrows and correct species and state symbols in the box. (2) ΔrH MgCO3(s) MgO(s) + CO2(g)
June 2024 (R), AS Unit 2, Q18(b)(ii) (2 marks): Calculate the enthalpy change for the thermal decomposition of magnesium carbonate, ∆rH . Include a sign and units in your answer. (2)
January 2024, AS Unit 2, Q22(a) (2 marks): Explain why ΔrH1 can also be described as an enthalpy change of formation. (2)
January 2024, AS Unit 2, Q22(b) (4 marks): The student carried out an experiment to determine the enthalpy change of reaction, ΔrH2 , in kJ mol–1, for Reaction 2. Reaction 2 MgO(s) + 2HCl(aq) → MgCl2(aq)
January 2024, AS Unit 2, Q22(c) (2 marks): Calculate the enthalpy change of reaction, ΔrH1 , for Reaction 1. Use your answer to (b), the data provided and the enthalpy cycle shown. [If you did not calcul
January 2024, AS Unit 3, Q4(c)(i) (1 mark): Calculate the energy transferred to the water. (1)
January 2024, AS Unit 3, Q4(c)(ii) (1 mark): Calculate the amount of ethanol burnt in moles. (1)
January 2024, AS Unit 3, Q4(c)(iii) (1 mark): Calculate the enthalpy change of combustion of ethanol in kJ mol–1, using your answers to (c)(i) and (c)(ii). Give your answer to an appropriate number of signi
January 2024, AS Unit 3, Q4(d) (3 marks): Whilst evaluating the method used in (c), the student found a diagram of an alternative apparatus as shown. pump stirrer thermometer copper coil water spirit bu
October 2023, AS Unit 1, Q19(a)(i) (2 marks): Calculate the mean energy density of this E10 fuel in MJ kg–1. Give your answer to an appropriate number of significant figures. (2)
October 2023, AS Unit 1, Q19(a)(iii) (1 mark): Calculate the energy released when 1500 cm3 of the E10 fuel is burned in excess oxygen, using your answers from (a)(i) and (a)(ii). [If you did not calculate a
October 2023, AS Unit 2, Q2 (1 mark): Which expression gives the standard enthalpy change, in kJ mol–1, for the reaction shown? BaCO3(s) → BaO(s) + CO2(g) ΔfH d values: BaCO3(s) = –1216 kJ mol–1 BaO
October 2023, AS Unit 2, Q3 (1 mark): The standard enthalpy changes of combustion for a series of alkanes are shown. ΔcH d / kJ mol–1 Alkane formula C2H6(g) –1560 C3H8(g) –2219 C4H10(l) –2877 C5H12(
October 2023, AS Unit 2, Q18(a)(ii) (2 marks): State what is meant by standard enthalpy change of neutralisation, ΔneutH d. (2)
October 2023, AS Unit 2, Q18(b)(i) (2 marks): Use the graph shown to determine the maximum temperature change, ΔT, in this experiment. You must show your working on the graph. (2) ΔT 28 26 Temperature / °C
October 2023, AS Unit 2, Q18(b)(ii) (3 marks): Calculate the enthalpy change of neutralisation using your answers to (a) and (b)(i). Give a sign and units with your answer. Assume: no energy is used to heat
October 2023, AS Unit 2, Q18(b)(iii) (2 marks): Explain how, if at all, the enthalpy change of neutralisation obtained in (ii) would differ if the heat capacity of the calorimeter was included in the calculat
October 2023, Unit 4, Q16(a)(ii) (3 marks): Calculate the standard enthalpy change for this reaction. . (3)
June 2023, AS Unit 2, Q1 (1 mark): The enthalpy level diagram for a reaction is shown. reactants ∆H Enthalpy products Progress of reaction Which is represented by this diagram? A Na(s) → Na(g) B
June 2023, AS Unit 2, Q2(a) (1 mark): The percentage error in this experiment is (1) A ±7.37 % B ±8.65 % C 14.7 % D 17.3 %
June 2023, AS Unit 2, Q2(b) (1 mark): In the calculation, the specific heat capacity of the liquid is taken to be 4.18 J g–1 °C–1 rather than the true value of 3.85 J g–1 °C–1. The use of 4.18 J g–1
June 2023, AS Unit 2, Q3 (1 mark): The enthalpy changes for two reactions are shown. 2Fe(s) + 1½O2(g) → Fe2O3(s) ΔrH = –824 kJ mol–1 + ½O2(g) → CO(g) ΔrH = –111 kJ mol–1 C(s) What is the enthalpy
June 2023, AS Unit 2, Q20(a)(iii) (2 marks): When petrol is used to power a car, the energy available is less than the theoretical maximum. When one kilogram of petrol powers a car, the energy used to move
June 2023, AS Unit 2, Q20(a)(iv) (2 marks): Give two reasons why the energy used to move the car is less than the theoretical maximum. (2)
January 2023, AS Unit 2, Q1(a) (1 mark): The measurement uncertainty in the thermometer used in the experiment is 0.5 °C for each reading. What is the percentage uncertainty in the temperature change o
January 2023, AS Unit 2, Q1(b) (1 mark): The student repeats the experiment but burns 0.30 g of methanol and uses 75.0 cm3 of water in the copper calorimeter. What is the expected temperature change in
January 2023, AS Unit 2, Q1(c) (1 mark): The student’s calculated enthalpy change of combustion of methanol is more exothermic than a data book value. What is a possible reason for this? (1) A heat los
January 2023, AS Unit 2, Q2 (1 mark): Which equation represents the standard enthalpy change of atomisation, ΔatH , of bromine? A ½Br2(l) → Br(g) B ½Br2(g) → Br(g) → 2Br(g) C Br2(l) D Br2(g) → 2Br(g
January 2023, AS Unit 2, Q22(e)(ii) (1 mark): Suggest why only a small amount of energy is used to maintain the temperature at 1100 K. (1)
January 2023, AS Unit 2, Q22(g)(i) (2 marks): Complete the enthalpy cycle. (2) Enthalpy cycle ΔrH NH3(g) + HNO3(aq) NH4NO3(aq) –32.6 kJ mol–1 kJ mol–1 NH4NO3(s) –220.2 kJ mol–1 kJ mol–1 N2(g) + 2H2(g) + 1½O
January 2023, AS Unit 2, Q22(g)(ii) (1 mark): Calculate the enthalpy change, ΔrH , in kJ mol–1 , for the reaction of NH3(g) with HNO3(aq). (1)
January 2023, AS Unit 3, Q2(a)(i) (1 mark): Give a reason why it is important to shield the apparatus from draughts. (1)
January 2023, AS Unit 3, Q2(b)(i) (1 mark): The student’s results are shown. Quantity Value Final water temperature / °C 29.1 Initial water temperature / °C 21.8 Temperature change / °C Mass of burner + e
January 2023, AS Unit 3, Q2(b)(ii) (3 marks): Calculate the enthalpy change of combustion of ethanol in kJ mol–1, using the student’s results. Give your answer to an appropriate number of significant figure
January 2023, AS Unit 3, Q2(b)(iii) (2 marks): In this procedure, after removing the burner there is a delay before the flame is extinguished. Explain the effect of this delay on the value of the enthalpy ch
January 2023, Unit 4, Q20(a)(ii) (2 marks): Calculate the enthalpy change of reaction, ΔrH d, for the cracking of butane. Include a sign and units with your answer. (2)
October 2022, AS Unit 2, Q2 (1 mark): Which equation shows the standard enthalpy change of formation of sodium chloride? A Na(s) + ½Cl2(g) → NaCl(s) B 2Na(s) + Cl2(g) → 2NaCl(s) → NaCl(s) C Na(g) +
October 2022, AS Unit 2, Q3 (1 mark): Some enthalpy changes of combustion are shown. Substance Enthalpy change of combustion / kJ mol−1 CH3CHO(l) −1167 C(s) −394 H2(g) −286 What is the enthalpy chan
October 2022, AS Unit 2, Q20(a) (4 marks): In the first experiment, the student determines the enthalpy change when hydrated copper(II) sulfate dissolves in water. CuSO4·5H2O(s) + aq → CuSO4(aq) 10.68 g
October 2022, AS Unit 2, Q20(b)(i) (2 marks): Complete the Hess cycle. (2) CuSO4(s) + 5H2O(l) CuSO4·5H2O(s)
October 2022, AS Unit 2, Q20(b)(ii) (2 marks): Calculate the enthalpy change when anhydrous copper(II) sulfate forms hydrated copper(II) sulfate. Include a sign and units. (2)
October 2022, Unit 4, Q6(b) (1 mark): Which of these statements best explains why only a small amount of energy is required to maintain this process? (1) A the catalyst increases the equilibrium yie
June 2022, AS Unit 2, Q1 (1 mark): Which equation represents the standard enthalpy change of formation, ΔfH d, for aluminium oxide? A 2Al(s) + 1½O2(g) → Al2O3(s) → Al2O3(s) B 2Al(s) + 3O(g) C 4Al
June 2022, AS Unit 2, Q18(a)(i) (1 mark): State the two standard conditions for this enthalpy change. (1)
June 2022, AS Unit 2, Q18(a)(iii) (2 marks): Draw a labelled enthalpy level diagram for the complete combustion of 2,2,4-trimethylpentane. (2)
June 2022, AS Unit 2, Q18(a)(iv) (3 marks): Calculate the heat energy released during the complete combustion of 1 dm3 of 2,2,4-trimethylpentane. [Density of 2,2,4-trimethylpentane = 0.692 g cm−3] (3)
June 2022, AS Unit 2, Q18(b)(i) (4 marks): Calculate the enthalpy change of combustion of ethanol. Give your answer to an appropriate number of significant figures, and include a sign and units. [Specifi
June 2022, AS Unit 2, Q18(b)(ii) (1 mark): The uncertainty in each thermometer reading is ±0.05 °C. Calculate the percentage uncertainty in the temperature rise in this experiment. (1)
June 2022, AS Unit 2, Q18(b)(iii) (2 marks): The student looked in a data book and found the actual value for the standard enthalpy change of combustion of ethanol was more exothermic than the experimental
June 2022, AS Unit 3, Q1(a)(i) (1 mark): Plot a graph of temperature against time on the grid. (1) 70.0 60.0 50.0 40.0 Temperature / °C 30.0 20.0 10.0 0.0 0.0 1.0 2.0 3.0 4.0 5.0 6.0 7.0 8.0 9.0 10.0 T
June 2022, AS Unit 3, Q1(a)(ii) (3 marks): Use the graph to determine the maximum temperature change, ΔT, in this experiment. You must show your working on the graph. (3) ΔT = °C
June 2022, AS Unit 3, Q1(b)(ii) (1 mark): Calculate the energy transferred in the reaction, in joules. Assume that the specific heat capacity of the solution is 4.2 J g–1°C–1. (1)
June 2022, AS Unit 3, Q1(b)(iii) (1 mark): State a second assumption, other than the specific heat capacity of the solution, that you have made in your calculation in (b)(ii). (1)
June 2022, AS Unit 3, Q1(b)(iv) (2 marks): Calculate the enthalpy change of the reaction, using your answers to (b)(i) and (b)(ii). (2)
June 2022, AS Unit 3, Q1(c) (2 marks): Identify two improvements in the experimental procedure that would improve the accuracy of the result, other than repeating the experiment. Justify your answers
June 2022, Unit 4, Q21(a)(i) (2 marks): Calculate the standard enthalpy change, ∆rH , for the reduction of iron(III) oxide by carbon. (2)
January 2022, AS Unit 2, Q1 (1 mark): Which are correct for the reaction shown? CH3COOH + KOH → CH3COO−K+ + H2O ΔH = –55.8 kJ mol−1 Type of reaction Type of enthalpy change A endothermic formation B
January 2022, AS Unit 2, Q2 (1 mark): Which equation does not represent a standard enthalpy change of atomisation? A Mg(s) → Mg(g) B Cl2(g) → 2Cl(g) C ½O2(g) → O(g) D Hg(l) → Hg(g) Use this space fo
January 2022, AS Unit 2, Q3 (1 mark): 5.20 g of sodium hydrogencarbonate is added to an excess of acid. The temperature increases and the energy change is calculated to be 1030 J. What is the enthal
January 2022, AS Unit 2, Q21(a)(i) (1 mark): Complete the table. (1)
January 2022, AS Unit 2, Q21(a)(ii) (4 marks): Calculate the enthalpy change of combustion, ΔcH, of 2‑methylpropan‑2‑ol. Give a sign and units in your answer. [Specific heat capacity of water = 4.18 J g−1 °C
January 2022, AS Unit 2, Q21(b)(i) (1 mark): State why no ∆fH d value has been given for oxygen. (1)
January 2022, AS Unit 2, Q21(b)(ii) (2 marks): Complete the Hess cycle. C4H10O(l) + O2(g) CO2(g) + H2O(l) 4C(s, graphite) + + (2)
January 2022, AS Unit 2, Q21(b)(iii) (2 marks): Calculate the standard enthalpy change of combustion of 2‑methylpropan‑2‑ol using the data in the table and the completed Hess cycle. (2)
January 2022, AS Unit 2, Q21(c) (2 marks): The value for ΔcH obtained in part (a)(ii) is much less exothermic than ΔcH d calculated in (b)(iii). Suggest two reasons for this other than non‑standard condi
January 2022, AS Unit 2, Q24(e)(ii) (3 marks): Sketch the reaction profile for the forward reaction on the axes provided. Include labels for ΔH and the activation energy (Ea). Energy Reaction progress (3)
January 2022, AS Unit 3, Q1(b)(i) (2 marks): Give two reasons why the student stirred the solution in Steps 3 and 4. (2)
January 2022, AS Unit 3, Q1(b)(ii) (2 marks): Use the graph to determine the maximum temperature change, ΔT, in this experiment. You must show your working on the graph. (2)
January 2022, AS Unit 3, Q1(b)(iii) (3 marks): Another student carried out the experiment using a polystyrene cup in place of the glass beaker. Explain how this student’s graph would be different. You may an
January 2022, AS Unit 3, Q1(c)(i) (2 marks): State two assumptions made in this calculation. You do not need to justify your answers. (2)
January 2022, AS Unit 3, Q1(c)(ii) (2 marks): The total percentage uncertainty in this experiment was 2.6 %. Show that the enthalpy change of 14.5 kJ mol–1 is consistent with a data book value of 14.8 kJ mo
October 2021, AS Unit 2, Q19(a)(ii) (2 marks): Calculate the heat energy required to raise the temperature of 100 g of water from 21.6 °C to 63.9 °C. [Specific heat capacity of water = 4.18 J g−1°C−1 ] (2)
October 2021, AS Unit 2, Q19(a)(iii) (3 marks): Use your answers to (a) (i) and (ii) to calculate a value for the enthalpy change of combustion of ethanol. Give your answer to an appropriate number of signifi
October 2021, AS Unit 2, Q19(a)(iv) (2 marks): The value of the enthalpy change of combustion from this experiment was very inaccurate. Give two reasons why this value was so inaccurate, apart from heat loss
October 2021, AS Unit 2, Q19(c) (3 marks): Enthalpy changes of combustion can be used to calculate the enthalpy change of formation of a compound. Standard enthalpy change of combustion, Substance ∆cH /
October 2021, AS Unit 3, Q3(a) (3 marks): Plot a graph of temperature against time on the grid. (3)
October 2021, AS Unit 3, Q3(b) (2 marks): Determine the maximum temperature change, ΔT, using your graph. You must show your working on the graph. (2) ΔT =
October 2021, AS Unit 3, Q3(c) (1 mark): The value of the enthalpy change from this experiment was −39.0 kJ mol−1. Give one possible reason why this value is different from a data book value of −61.4 k
October 2021, AS Unit 3, Q3(d)(i) (1 mark): Calculate the enthalpy change of hydration for the conversion of anhydrous copper(II) sulfate to hydrated copper(II) sulfate crystals. (1)
October 2021, AS Unit 3, Q3(d)(ii) (1 mark): Give one possible reason why the enthalpy change of hydration in (d)(i) could not be found directly by experiment. (1)
October 2021, Unit 6, Q3(a) (1 mark): Give a reason why a polystyrene cup was used instead of a glass beaker in Step 1. (1)
October 2021, Unit 6, Q3(b) (3 marks): The temperature rise was 12.5 °C. Calculate the enthalpy change for the formation of this solution of lithium chloride. Include a sign and units in your answer.
October 2021, Unit 6, Q3(d) (5 marks): The temperature rise in this experiment was lower than expected, due to heat loss to the surroundings. Describe changes to the procedure that would give a more
June 2021, AS Unit 2, Q1 (1 mark): Which is the correctly labelled reaction profile for an exothermic reaction? Enthalpy Ea Reactants A ∆H Products Reaction pathway Enthalpy ∆H Reactants B Ea Pro
June 2021, AS Unit 2, Q2 (1 mark): The equation for a reaction is 2C(s) + O2(g) → 2CO(g) Which is the correct symbol for the enthalpy change for this reaction? A ΔatH B ΔcH C ΔfH D ΔrH
June 2021, AS Unit 2, Q19(a) (2 marks): Write an equation for the reaction. Include state symbols in your answer. (2)
June 2021, AS Unit 2, Q19(b) (3 marks): A student carried out an experiment to determine the enthalpy change of the reaction. A sample of 0.50 g of magnesium powder was added to 25 cm3 of 0.20 mol dm−
June 2021, AS Unit 2, Q19(c)(i) (2 marks): The results obtained are given in the table. Plot the results on the grid. (2) Time Temperature / minutes / °C 0 22.2 1 22.0 2 22.0 Mg added 3 39.6 4 41.8 5 40.
June 2021, AS Unit 2, Q19(c)(ii) (2 marks): Use your graph to determine the maximum change in temperature. You must show your working on the graph. (2) ΔT =
June 2021, AS Unit 2, Q19(d) (4 marks): Calculate the standard molar enthalpy change for the reaction, using your answers to (b) and (c)(ii). Include a sign and units in your answer. [Specific heat ca
June 2021, AS Unit 2, Q22(b)(ii) (4 marks): The standard enthalpy change of formation for phosgene is ΔfH = –220.1 kJ mol–1. Complete the Hess cycle and determine the standard enthalpy change of formation
January 2021, AS Unit 2, Q11 (1 mark): The table shows the amount of energy released per gram when some alkanes are burned in excess oxygen under standard conditions. Energy released Alkane / kJ g−1
January 2021, AS Unit 2, Q12 (1 mark): The enthalpy changes for two reactions are shown. H+(aq) + OH−(aq) → H2O(l) ΔrH = −57.2 kJ mol−1 CH3COOH(aq) + OH−(aq) → CH3COO−(aq) + H2O(l) ΔrH = −56.0 kJ mol
January 2021, AS Unit 2, Q21(b) (5 marks): Sodium ethanoate is a component of reusable hand warmers. In use, a supersaturated solution of sodium ethanoate recrystallises to form solid hydrated sodium eth
January 2021, AS Unit 2, Q21(c) (5 marks): Ammonium ethanoate, CH3COONH4(s), is used to control the pH of foods. It can be formed by the reaction of pure ethanoic acid, CH3COOH(l), with ammonium carbonat
January 2021, AS Unit 3, Q3(c)(i) (2 marks): Calculate the enthalpy change, ΔH1 , for the reaction between MCO3 and hydrochloric acid in kJ mol−1. Include a sign with your answer. (2)
January 2021, AS Unit 3, Q3(c)(ii) (1 mark): Using your answer to (c)(i), calculate the enthalpy change, ΔrH , for the thermal decomposition of this Group 2 carbonate in kJ mol−1. Include a sign with your
October 2020, AS Unit 2, Q2 (1 mark): The standard enthalpy change of neutralisation for the reaction between sodium hydroxide solution and hydrochloric acid is –56 kJ mol–1. Which row in the table
October 2020, AS Unit 2, Q10(a) (1 mark): Which symbol represents the enthalpy change for the reaction R → P? (1) A u B v C w D x
October 2020, AS Unit 2, Q10(b) (1 mark): Which symbol represents the activation energy of the reaction P → R? (1) A u B v C w D x
October 2020, AS Unit 2, Q10(c) (1 mark): Hess’s Law can be applied to this system. Which expression is correct? (1) A v + x = u + w B w + x = u C u – w = v D u – v = x
October 2020, AS Unit 2, Q13(a)(i) (1 mark): Add arrowheads and stoichiometric coefficients to the Hess’s Law diagram. (1) 3C(s) + 4H2(g) C3H8(g) CO2(g) + H2O(l)
October 2020, AS Unit 2, Q13(a)(ii) (2 marks): Use the data at the start of the question and your Hess’s Law diagram to calculate the standard enthalpy change of formation of propane. Include a sign and unit
October 2020, AS Unit 2, Q13(b)(i) (2 marks): Explain why the increases in the values of ΔcH are similar. (2)
October 2020, AS Unit 2, Q13(b)(ii) (2 marks): The increase in the value of ΔcH from butane to pentane is smaller than any other increase. Suggest an explanation for this. (2)
October 2020, AS Unit 2, Q15(b)(i) (3 marks): Student A used a calorimetric method, reacting a 50.0 cm3 sample of the solution with excess powdered zinc. AgNO3(aq) + ½Zn(s) → ½Zn(NO3)2(aq) + Ag(s) ΔrH = –36
October 2020, AS Unit 2, Q15(b)(iii) (2 marks): The students’ values were different from the data book value. Student A’s value was lower and student B’s value was higher. Give a possible reason for each diff
October 2020, AS Unit 3, Q4(a)(i) (1 mark): Give a reason why an excess of sodium hydroxide was used. (1)
October 2020, AS Unit 3, Q4(a)(ii) (1 mark): The diagram shows part of the thermometer when the temperature had reached its maximum. 30 20 Record the temperature in the table of results and then complete t
October 2020, AS Unit 3, Q4(b) (4 marks): Calculate the enthalpy change of neutralisation of hydrochloric acid. Include a sign and units in your answer. [Assume: the density of both solutions and the mi
October 2020, AS Unit 3, Q4(c) (2 marks): The experiment was repeated using a glass beaker instead of a polystyrene cup. Explain how the value obtained for the enthalpy change of neutralisation would be
January 2020, AS Unit 2, Q1 (1 mark): 9, of 1 Which equation represents the standard enthalpy change of formation, ǻfH hydrogen iodide? A H(g) + I(g) → HI(g) B H2(g) + I2(s) → 2HI(g) C ½H2(g) + ½I2(
January 2020, AS Unit 2, Q2 (1 mark): When 50 cm3 of hydrochloric acid of concentration 2.0 mol dm−3 is added to 50 cm3 of sodium hydroxide solution of concentration 2.0 mol dm−3, the temperature in
January 2020, AS Unit 2, Q15(a)(i) (2 marks): State why different volumes of water are used in the two experiments. Justify your answer. (2)
January 2020, AS Unit 2, Q15(a)(ii) (3 marks): Calculate the enthalpy change of solution, ǻsolnH, in kJ mol−1, for the anhydrous salt, CuSO4 . ⎡ Assume: heat capacity of the solution = 4.2 J g−1 °C−1 ⎣⎢ dens
January 2020, AS Unit 2, Q15(a)(iii) (1 mark): Complete the Hess cycle by adding two arrowheads. (1) ǻrH CuSO4(s) + 5H2O(l) CuSO4.5H2O(s) ǻsolnH(CuSO4) ǻsolnH(CuSO4.5H2O) CuSO4(aq)
January 2020, AS Unit 2, Q15(a)(iv) (2 marks): Calculate the value for the enthalpy change ǻrH, in kJ mol−1, for the conversion of the anhydrous salt to the hydrated salt. Use the value from the table for ǻs
January 2020, AS Unit 2, Q15(b) (2 marks): The hydration of anhydrous copper(II) sulfate is reversible. CuSO4(s) + 5H2O(l) CuSO4.5H2O(s) The forward reaction is exothermic. The temperature changes for bo
January 2020, AS Unit 2, Q15(c) (2 marks): Describe the processes that occur when solid copper(II) sulfate dissolves in water. (2)
January 2020, AS Unit 3, Q2(a)(i) (2 marks): Calculate the number of moles of magnesium in the 10 cm length of ribbon used in this experiment. [Ar value: Mg = 24.3] (2)
January 2020, AS Unit 3, Q2(a)(ii) (4 marks): Calculate the enthalpy change for this reaction including a sign and units. Give your answer to an appropriate number of significant figures. Data: Specific hea
January 2020, AS Unit 3, Q2(b)(ii) (2 marks): Suggest one way of reducing the percentage uncertainty in measuring the temperature change without changing the apparatus or just repeating the experiment. Just
January 2020, AS Unit 3, Q2(c) (2 marks): One student carried out the same experiment but used a glass beaker instead of a polystyrene cup. State how this would affect the value of the enthalpy change o
January 2020, AS Unit 3, Q2(d) (2 marks): Explain why the magnesium ribbon was cleaned with sandpaper before being weighed. (2)
June 2019, AS Unit 2, Q9 (1 mark): Use the data shown. ¨H = −858 kJ mol–1 CH4(g) + 2F2(g) → CF4(g) + 2H2(g) ¨H = −933 kJ mol–1 C(s) + 2F2(g) → CF4(g) What is the standard enthalpy change of forma
June 2019, AS Unit 2, Q11 (1 mark): Which equation represents the standard enthalpy change of atomisation of bromine? A Br2(g) → 2Br(g) B Br2(l) → 2Br(g) C ½Br2(l) → Br(g) D ½Br2(g) → Br(g) Use th
June 2019, AS Unit 2, Q12 (1 mark): In an experiment, 50.0 cm3 of 1.0 mol dm−3 HCl(aq) reacts with 50.0 cm3 of 1.0 mol dm−3 NaOH(aq). The energy released = 2500 J. The specific heat capacity of th
June 2019, AS Unit 2, Q20(b)(i) (2 marks): Explain, in terms of energy changes, why magnesium carbonate is insoluble in water. (2)
June 2019, AS Unit 2, Q20(b)(ii) (2 marks): The Hess cycle and data to calculate the enthalpy change for the thermal decomposition of MgCO3 are shown. Mg(s) + C(s) + 1½O2(g) MgCO3(s) MgO(s) + CO2(g) 9 / k

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