2 (a) The order of reactivity for some metals is shown in Fig. 2.1. most reactive metal A sodium calcium metal B zinc iron least reactive copper Fig. 2.1 (i) Suggest the identities of metals A and B. A … B … [1] (ii) State two observations for the reaction of sodium with water. 1 … 2 … [2] (b) Sodium is in Group I of the Periodic Table. Iron is a transition element. Describe two physical properties of iron that show that it is different from sodium. 1 … 2 … [2] (c) Brass is an alloy of zinc and one other metal. State the name of this other metal. … [1] (d) Recycling metals uses less energy and costs less money than extracting the metals from their ores. State one other reason why metals need to be recycled. … … [1] (e) Sodium and chlorine react together in an exothermic reaction to form sodium chloride. (i) State what is meant by exothermic. … … [1] (ii) Fig. 2.2 shows the electronic structures of a sodium ion, Na+, and a chloride ion, Cl–, in sodium chloride. sodium ion chloride ion ×× × × ×× ×× ×××× ×× × ×× × × ×× ×× × ×× ×× Fig. 2.2 Complete Fig. 2.3 to show the electronic structures of a sodium atom, Na, and a chlorine atom, Cl. sodium atom chlorine atom Fig. 2.3 [2] [Total: 10]

2(a)(i) A potassium AND B magnesium / aluminium ; 1 2(a)(ii) any two from: fizzes / bubbles ; gets smaller ; floats ; moves ; 2 2(b) any two from: (iron has) high(er) density / ORA ; (iron has) high(er) melting point / ORA ; (iron is) magnetic / ORA ; 2 2(c) copper ; 1 2(d) metals are finite (resources) / will run out ; 1 2(e)(i) (thermal) energy is released ; 1 2(e)(ii) (sodium atom) 2, 8, 1 ; (chlorine atom) 2, 8, 7 ; 2

8 (a) An atom of lead is represented by the symbol shown. 207 82 Pb (i) Deduce the number of electrons and number of neutrons in this atom. electrons … neutrons … [2] (ii) The proton number (atomic number) of lead is 82. Define the term proton number. … … [1] (iii) State the charges of protons, neutrons and electrons. protons … neutrons … electrons … [1] (b) Lead is extracted from molten lead(II) bromide using the apparatus shown in Fig. 8.1. molten lead(II) bromide – + low voltage d.c. supply Fig. 8.1 (i) Name the process shown in Fig. 8.1. … [1] (ii) State the name of the electrode at which lead forms. … [1] (c) Lead is extracted from lead(II) oxide, PbO, by heating with carbon. Carbon dioxide is also made in this endothermic reaction. (i) Describe what is meant by an endothermic reaction. … … [1] (ii) Complete the word equation for this reaction. lead + + [1] (iii) Circle the word to show whether lead(II) oxide is oxidised or reduced in this reaction. Explain your answer. oxidised reduced explanation … … [1] (d) A teacher has a different compound of lead. When this compound of lead reacts with dilute hydrochloric acid, carbon dioxide is formed. Suggest the name of this compound of lead. … [1] [Total: 10]

8(a)(i) (electrons) 82 ; (neutrons) 125 ; 2 8(a)(ii) the number of protons in the nucleus of an atom ; 1 8(a)(iii) (protons) +1 (neutrons) no charge (electrons) -1 ; all three needed for one mark 1 8(b)(i) electrolysis ; 1 8(b)(ii) cathode ; 1 8(c)(i) takes in, heat / energy ; 1 8(c)(ii) ; 1 8(c)(iii) reduced (circled) AND (explanation) loses oxygen ; 1 8(d) lead carbonate / PbCO3 ; 1 To earn marks, you must correctly state 82 electrons and 125 neutrons. You need to define proton number as the number of protons in the nucleus of an atom. For charges, you must state +1 for protons, no charge for neutrons, and -1 for electrons, with all three correct for the mark. You must name the process as 'electrolysis' and the electrode where lead forms as the 'cathode'. For the reaction with carbon, you need to state that it 'takes in heat/energy', draw the correct energy profile diagram, and explain that lead(II) oxide is 'reduced' because it 'loses oxygen'. Finally, you must name 'lead carbonate' or 'PbCO3' as the compound that causes acid rain.

2 Fig. 2.1 shows the energy level diagrams for four different compounds dissolving in water. energy reactants sodium hydroxide products – 44.5 kJ/mol progress of reaction energy reactants ammonium nitrate products + 25.7 kJ/mol progress of reaction energy reactants potassium hydroxide products – 57.6 kJ/mol progress of reaction energy reactants sodium chloride products + 3.9 kJ/mol progress of reaction Fig. 2.1 (a) Dissolving in water is an endothermic reaction for two of these four compounds. State the names of these two compounds. Use the energy level diagrams to explain your answer. compound 1 … compound 2 … explanation … … … [2] (b) A teacher dissolves some solid sodium hydroxide in water to make a solution. The teacher records the initial temperature of the water before adding the sodium hydroxide. The teacher records the temperature of the solution every 10 s after adding the sodium hydroxide. Table 2.1 shows the results. Table 2.1 initial temperature of water / °C temperature of solution / °C 10 s 20 s 30 s 40 s 50 s 60 s 22.0 28.0 34.5 33.0 31.5 30.5 29.0 (i) Name two pieces of equipment the teacher uses to collect the data in Table 2.1. 1 … 2 … [2] (ii) Describe the changes in the temperature of the solution over the 60 s. Explain why these changes occur. changes in temperature … … explanation … … … [3] (iii) Calculate the maximum temperature change shown by the data in Table 2.1. maximum temperature change = … °C [1] [Total: 8]

2(a) ammonium nitrate AND sodium chloride ; an upwards arrow shows, energy change is positive / energy has been taken in / energy of the products is greater than the energy of the reactants ; 2 2(b)(i) thermometer / temperature probe ; stop-watch; 2 2(b)(ii) increases then decreases ; (increases because) energy given out / exothermic reaction ; (decreases because) reaction is finished (and so it cools) ; 3 2(b)(iii) (34.5 – 22.0 =) 12.5 (oC) ; 1

5 Some gas ovens use methane as a fuel, other gas ovens use propane. (a) Complete and balance the equation for the complete combustion of propane. C3H8 + 5O2 … + … [2] (b) Fig. 5.1 shows the energy level diagrams for the combustion of methane and the combustion of propane. The diagrams are drawn to the same scale. energy progress of reaction methane reactants products energy progress of reaction reactants products propane Fig. 5.1 (i) Explain how Fig. 5.1 shows that both reactions are exothermic. … … … … [2] (ii) Use Fig. 5.1 to state two differences between the energy changes that happen during the combustion of methane and the combustion of propane. 1 … … 2 … … [2] (c) When the air supply to an oven is limited, carbon monoxide is formed. State one adverse effect of carbon monoxide. … … [1] [Total: 7]

5(a) CO2 AND H2O given as products ; balanced equation 3CO2 + 4H2O ; 2 5(b)(i) (in both reactions) energy is given out ; energy change is negative / energy of the products is lower than energy of the reactants OWTTE ; 2 5(b)(ii) propane has a higher activation energy ; propane gives out more energy / gives a more exothermic reaction ; 2 5(c) toxic / poisonous ; 1

17 Which word is used to describe a reaction that takes in heat energy from the surroundings? A endothermic B exothermic C oxidation D reduction

Answer: A To earn the mark, a student must correctly identify 'endothermic' as the term for a reaction that takes in heat energy from the surroundings.

Cambridge IGCSE Combined Science · 0653

IGCSE Combined Science (0653) Chemical energetics past paper questions

Revise IGCSE Combined Science (0653) — Chemical energetics with real Cambridge past-paper questions grouped by topic, each shown with its marking scheme. Working one topic at a time targets exactly the skill each question tests.

131 free questions from 2016–2021, each with its marking scheme. Open the full topical bank to filter by subtopic, paper, and year.

Chemical energetics in IGCSE Combined Science 0653 exams, 2020–2025

Across 2020–2025, Chemical energetics accounted for 130 questions worth 737 marks in Cambridge IGCSE Combined Science (0653) papers.

By year
Year	Questions	Marks
2020	19	115
2021	17	66
2022	24	153
2023	23	116
2024	25	166
2025	22	121

Most-tested subtopics

C5.1 Exothermic and endothermic reactions675 marks

Appears in

Paper 1 · 28 qs
Paper 2 · 34 qs
Paper 3 · 21 qs
Paper 4 · 22 qs
Paper 5 · 9 qs
Paper 6 · 16 qs

All most-tested Combined Science topics

2021 Oct/Nov · Paper 3 · Q2 · 10 marks
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2021 Feb/Mar · Paper 3 · Q8 · 10 marks
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2021 Oct/Nov · Paper 4 · Q2 · 8 marks
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2021 May/Jun · Paper 4 · Q5 · 7 marks
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2021 Feb/Mar · Paper 1 · Q17 · 1 mark
Marking scheme
Mark scheme — 2021 Paper 1 Q17
Answer: A
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