Ten original Paper 1 multiple-choice questions with answers and a one-line reason, plus three structured questions worked fully, each showing Q = mcθ then dividing by the number of moles, with units and sign. All questions are original and written in SPM style.
Use these questions to test yourself after revising. Cover the answers, attempt each one, then check your method. Take the specific heat capacity of aqueous solutions as 4.2 J g⁻¹ °C⁻¹ and the density of every solution as 1 g cm⁻³, as SPM questions do. These are original questions in SPM style, not past-year papers.
Paper 1, multiple choice
1. Which of the following is an endothermic process? A. Combustion of ethanol B. Neutralisation of an acid by an alkali C. Thermal decomposition of copper(II) carbonate D. Reaction of magnesium with dilute acid
Answer: C. Thermal decomposition absorbs heat from the surroundings, so it is endothermic; the other three release heat.
2. During a reaction the temperature of the mixture rises. What can you conclude about the heat change, ΔH? A. It is positive B. It is negative C. It is zero D. It cannot be determined
Answer: B. A temperature rise means heat is released (exothermic), so ΔH is negative.
3. On an energy level diagram the products are drawn lower than the reactants. The reaction is: A. endothermic with positive ΔH B. endothermic with negative ΔH C. exothermic with positive ΔH D. exothermic with negative ΔH
Answer: D. Products lower than reactants means energy is released, so the reaction is exothermic and ΔH is negative.
4. On an energy level diagram, the activation energy is: A. the difference between the reactant and product energy levels B. the energy released when new bonds form C. the minimum energy needed to start the reaction D. the total energy of the products
Answer: C. The activation energy is the “hump” from the reactant level to the peak, the minimum energy to start the reaction. Option A describes ΔH.
5. The heat of neutralisation is the heat change when: A. one mole of an acid reacts completely B. one mole of water is formed from an acid and an alkali C. one mole of salt is formed D. one mole of hydrogen gas is released
Answer: B. Heat of neutralisation is defined per one mole of water formed.
6. A weak acid gives a lower heat of neutralisation than a strong acid because: A. the weak acid is always more dilute B. heat is absorbed to complete the ionisation of the weak acid C. the weak acid forms less salt D. the neutralisation becomes endothermic
Answer: B. Some heat is used to fully ionise the weak acid, so less heat is released overall.
7. In an experiment to find the heat of displacement of copper by zinc, which mass is used in Q = mcθ? A. the mass of zinc added B. the mass of copper deposited C. the mass of the copper(II) sulfate solution D. the combined mass of zinc and copper
Answer: C. The solution is what changes temperature, so its mass is used in Q = mcθ.
8. The heat of combustion of a fuel is the heat released when: A. the fuel is burnt in a limited supply of oxygen B. one mole of the fuel is completely burnt in excess oxygen C. one gram of the fuel is burnt D. the fuel evaporates
Answer: B. Heat of combustion is per one mole, completely burnt in excess oxygen.
9. The experimental heat of combustion of ethanol is lower than the accepted value mainly because: A. the thermometer is always inaccurate B. heat is lost to the surroundings and to the container C. too much ethanol is used D. water has a low specific heat capacity
Answer: B. Heat loss to the surroundings and the metal can, plus incomplete combustion, lowers the experimental value.
10. When 100 cm³ of a solution is warmed by 6.0 °C, the heat released is: A. 0.252 kJ B. 2.52 kJ C. 25.2 kJ D. 252 kJ
Answer: B. Q = mcθ = 100 × 4.2 × 6.0 = 2520 J = 2.52 kJ.
Paper 2, structured questions
Structured Question 1, Heat of neutralisation
50.0 cm³ of 2.0 mol dm⁻³ hydrochloric acid at 28.0 °C is added to 50.0 cm³ of 2.0 mol dm⁻³ sodium hydroxide solution at 28.0 °C. The highest temperature reached by the mixture is 41.4 °C.
(a) Calculate the heat released. (b) Calculate the number of moles of water formed. (c) Hence calculate the heat of neutralisation, giving the sign.
Model answer. (a) Total volume = 50.0 + 50.0 = 100 cm³, so mass m = 100 g. Temperature change θ = 41.4 − 28.0 = 13.4 °C. Heat released Q = mcθ = 100 × 4.2 × 13.4 = 5628 J = 5.628 kJ. (b) Moles of HCl = 0.0500 dm³ × 2.0 mol dm⁻³ = 0.10 mol; moles of NaOH = 0.10 mol. HCl + NaOH → NaCl + H₂O, so moles of water formed = 0.10 mol. (c) Heat of neutralisation = Q ÷ moles of water = 5.628 kJ ÷ 0.10 mol = 56.28 kJ mol⁻¹. The temperature rose, so the reaction is exothermic: ΔH = −56.3 kJ mol⁻¹.
Structured Question 2, Heat of displacement
Excess zinc powder is added to 100 cm³ of 0.50 mol dm⁻³ copper(II) sulfate solution. The temperature rises from 29.0 °C to 40.5 °C.
(a) Calculate the heat released. (b) Calculate the number of moles of copper displaced. (c) Hence calculate the heat of displacement, with its sign, and state which mass you used in part (a) and why.
Model answer. (a) Mass of solution m = 100 g. θ = 40.5 − 29.0 = 11.5 °C. Q = mcθ = 100 × 4.2 × 11.5 = 4830 J = 4.83 kJ. (b) Zinc is in excess, so copper(II) sulfate is limiting. Moles of Cu²⁺ = 0.100 dm³ × 0.50 mol dm⁻³ = 0.050 mol, so moles of copper displaced = 0.050 mol. (c) Heat of displacement = 4.83 kJ ÷ 0.050 mol = 96.6 kJ mol⁻¹. Temperature rose, so exothermic: ΔH = −96.6 kJ mol⁻¹. The mass used is the mass of the solution (100 g), because it is the solution whose temperature changes, not the zinc or the copper.
Structured Question 3, Heat of combustion
0.92 g of ethanol (molar mass 46 g mol⁻¹) is burnt completely and the heat is used to warm 200 cm³ of water. The temperature of the water rises from 30.0 °C to 55.0 °C.
(a) Calculate the heat released to the water. (b) Calculate the number of moles of ethanol burnt. (c) Hence calculate the heat of combustion, with its sign. (d) Sketch and describe the energy level diagram for this reaction. (e) Suggest one reason the value found is smaller than the accepted value.
Model answer. (a) Mass of water m = 200 g. θ = 55.0 − 30.0 = 25.0 °C. Q = mcθ = 200 × 4.2 × 25.0 = 21 000 J = 21 kJ. (b) Moles of ethanol = mass ÷ molar mass = 0.92 ÷ 46 = 0.020 mol. (c) Heat of combustion = 21 kJ ÷ 0.020 mol = 1050 kJ mol⁻¹. Combustion releases heat, so exothermic: ΔH = −1050 kJ mol⁻¹. (d) The vertical axis is labelled Energy. The reactants (ethanol + oxygen) are drawn at a higher level; the products (carbon dioxide + water) are drawn at a lower level. The downward arrow between them is ΔH, marked negative, showing energy released to the surroundings. (e) Heat is lost to the surroundings and to the container, and combustion may be incomplete, so less heat reaches the water and the calculated value is lower than the accepted value.
Marking yourself
Give yourself the marks only when the working shows every step: Q = mcθ with the correct mass, the number of moles from the definition, the division, and a final answer in kJ mol⁻¹ carrying a sign. If any of those is missing, note which one, that is the habit to drill. A one-to-one teacher can mark your structured answers line by line so the method becomes automatic before the exam. Once these feel secure, revisit the common mistakes and worked examples for this chapter to lock the method in.
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