Chemical reactions — IGCSE Chemistry (0620) questions by topic
Distinguishing physical from chemical changes, working out which conditions shift the equilibrium yield of hydrogen iodide, choosing the right apparatus to measure a gas-producing reaction's rate, and interpreting timed results from a zinc-and-acid experiment are the recurring content in this topic, worth 1 to 19 marks across 80 real questions from 2023 to 2025 papers.
Identify, describe, explain, state and complete are the leading command words, and explain in a rate or equilibrium question means linking a stated change, such as concentration or temperature, to particle collisions or Le Chatelier's principle, not just naming the change. Because equilibrium and rate questions punish a plausible-sounding but incomplete mechanism, drafting the explanation and checking it against instant marking is a fast way to confirm the reasoning is complete.
May–June 2025, Paper 11
When a small piece of a Group I metal is placed into a large beaker of cold water, a reaction occurs. Four statements about this reaction are listed. 1 The metal melts. 2 Hydrogen…
Answer this question and get it marked →The equation for the decomposition of hydrogen peroxide is shown. 2H2O2 → 2H2O + O2 The reaction is exothermic. When a small amount of a catalyst is added, the oxygen is produced…
Answer this question and get it marked →The equation for the reaction between copper(II) oxide and carbon is shown. 2CuO + C → 2Cu + CO2 Which statement about this reaction is correct? A CuO is reduced. B CO2 is…
Answer this question and get it marked →May–June 2025, Paper 12
Which process involves a chemical change? A dissolving copper(II) sulfate B distilling ethanol C freezing water D neutralising copper(II) oxide
Answer this question and get it marked →The total volume of gas produced in two different experiments is measured against time. A graph of the results of the two experiments is shown. The graph plots total volume of gas…
Answer this question and get it marked →The equation for the reaction of sulfur dioxide with oxygen is shown. 2SO2 + O2 <= 2SO3 What is meant by the symbol <= (two half-arrows pointing in opposite directions)? A redox…
Answer this question and get it marked →Which reactions are redox reactions? 1 the incomplete combustion of propane 2 the rusting of iron 3 the reaction of aqueous chloride ions with acidified aqueous silver nitrate 4…
Answer this question and get it marked →May–June 2025, Paper 13
Steam reacts with carbon to produce carbon monoxide and hydrogen. C(s) + H2O(g) - CO(g) + H2(g) Which substance is reduced in the reaction? A C B CO C H2 D H2O
Answer this question and get it marked →May–June 2025, Paper 21
The graph shows the results of adding excess calcium carbonate to hydrochloric acid at 50 °C and at 30 °C. Only the temperature is changed. The graph plots total volume of carbon…
Answer this question and get it marked →May–June 2025, Paper 22
Which statement describes the effect of adding a catalyst to a chemical reaction? A The activation energy, Ea, of the reaction is increased. B The enthalpy change, deltaH, of the…
Answer this question and get it marked →Which equations show the underlined species acting as a reducing agent? (The underlined species is shown in [square brackets].) 1 [Fe2O3] + 3CO - 2Fe + 3CO2 2 [Fe] + CuSO4 - FeSO4…
Answer this question and get it marked →May–June 2025, Paper 23
The rate of reaction between magnesium and dilute hydrochloric acid is increased by increasing the concentration of the acid. How does this affect the reacting particles?…
Answer this question and get it marked →The reaction between aqueous iron(III) ions, Fe3+, and aqueous thiocyanate ions, SCN-, is reversible. The equation for the reaction is shown. Fe3+(aq) + SCN-(aq) <= FeSCN2+(aq)…
Answer this question and get it marked →The equation for the reaction between iron(II) sulfate and bromine is shown. 6FeSO4 + 3Br2 - 2Fe2(SO4)3 + 2FeBr3 Which row identifies the oxidising agent and the reducing agent?…
Answer this question and get it marked →The equation represents a redox reaction. 2Al + Fe2O3 - 2Fe + Al2O3 What is the change in the oxidation number of iron in this reaction? A from +2 to +3 B from +2 to 0 C from +3…
Answer this question and get it marked →May–June 2025, Paper 32
Select two processes that show a chemical change. Tick two boxes. boiling water burning methane dissolving salt mixing ink and water rusting of iron
Answer this question and get it marked →May–June 2025, Paper 33
This question is about chemical reactions and their energy changes. Tick one box that shows a chemical change. - boiling ethanol - decomposing vegetation - dissolving salt -…
Answer this question and get it marked →May–June 2025, Paper 41
Methanol, CH3OH, is manufactured by the reaction between hydrogen and carbon monoxide. An equilibrium mixture is produced. 2H2(g) + CO(g) ⇌ CH3OH(g) State what happens to the…
Answer this question and get it marked →May–June 2025, Paper 43
Ethanoic acid is manufactured in the reaction between methanol and carbon monoxide. An equilibrium mixture is produced. CH3OH(g) + CO(g) (reversible) CH3COOH(g) State two…
Answer this question and get it marked →May–June 2025, Paper 53
Complete Table 1.1. Table 1.1 has columns: experiment volume of aqueous sodium thiosulfate / cm^3 volume of distilled water / cm^3 volume of dilute hydrochloric acid / cm^3 time…
Answer this question and get it marked →May–June 2024, Paper 11
Which diagram (A, B, C or D) represents a chemical change? The four particle diagrams show different rearrangements of atoms/molecules; the chemical change is the one in which the…
Answer this question and get it marked →A method used to investigate the rate of reaction of calcium carbonate with dilute hydrochloric acid under different conditions: place 50 cm³ of dilute hydrochloric acid in a…
Answer this question and get it marked →The rate of reaction between magnesium and hydrochloric acid is investigated; the total volume of hydrogen given off is measured at different times. A graph of total volume of…
Answer this question and get it marked →May–June 2024, Paper 12
Which of the processes produces a physical change? A thermal decomposition of calcium carbonate B addition of sodium chloride to water C addition of magnesium to hydrochloric acid…
Answer this question and get it marked →A known mass of gaseous ammonia and excess gaseous hydrogen chloride react together to make solid ammonium chloride. Line X shows the total mass of ammonium chloride produced over…
Answer this question and get it marked →May–June 2024, Paper 13
Which process is a physical change? A firework exploding B burning wood C chocolate melting D iron rusting
Answer this question and get it marked →Magnesium reacts with dilute hydrochloric acid, HCl, to produce hydrogen gas. Which row identifies the reaction conditions that give the fastest rate of reaction? (columns:…
Answer this question and get it marked →May–June 2024, Paper 21
When calcium carbonate is heated strongly, a gas is given off. Which word describes this change? A chemical B exothermic C physical D reduction
Answer this question and get it marked →Powdered magnesium carbonate is added to excess dilute hydrochloric acid. The total volume of gas produced is measured over time; a graph shows the volume rising and levelling off…
Answer this question and get it marked →Which statements explain why increasing the temperature changes the rate of a chemical reaction? 1 It increases the activation energy. 2 It increases the frequency of collisions…
Answer this question and get it marked →Hydrogen is made by reacting carbon with steam: C(s) + H2O(g) ⇌ H2(g) + CO(g) The forward reaction is endothermic. Which row describes changes in the pressure and the temperature…
Answer this question and get it marked →May–June 2024, Paper 22
A student adds excess magnesium ribbon to 10 cm³ of 0.5 mol/dm³ sulfuric acid. The hydrogen gas produced is collected and its total volume measured every 10 seconds. The…
Answer this question and get it marked →The equation represents the reversible reaction between ethene and steam: C2H4(g) + H2O(g) ⇌ C2H5OH(g) ΔH is negative Which row describes the conditions that produce the greatest…
Answer this question and get it marked →May–June 2024, Paper 23
Which process is a physical change? A burning a piece of magnesium B reacting calcium carbonate with hydrochloric acid C melting an ice cube D the rusting of an iron nail
Answer this question and get it marked →The equation for the decomposition of hydrogen peroxide, H2O2, is shown: 2H2O2 → 2H2O + O2 In an experiment, the total volume of oxygen produced is 100 cm³. The experiment is…
Answer this question and get it marked →Nitrogen reacts with hydrogen to form ammonia in the presence of an iron catalyst. The reaction is reversible: N2(g) + 3H2(g) ⇌ 2NH3(g) Which statement about this reaction is…
Answer this question and get it marked →May–June 2024, Paper 31
Large pieces of solid sulfur burn in excess oxygen to produce sulfur dioxide gas. Complete the equation by adding the missing state symbol: S() + O2(g) → SO2(g)
Answer this question and get it marked →May–June 2024, Paper 32
Solid nitrogen pentoxide, N2O5, decomposes to produce nitrogen dioxide gas and oxygen gas. Complete the equation by adding the missing state symbols: 2N2O5(s) → 4NO2() + O2()
Answer this question and get it marked →May–June 2024, Paper 33
Dilute hydrochloric acid reacts with small pieces of calcium carbonate: 2HCl(aq) + CaCO3(s) → CaCl2(aq) + H2O(l) + CO2(g) State the meaning of the state symbol (aq).
Answer this question and get it marked →May–June 2024, Paper 41
This question is about the elements sodium and fluorine and the compound sodium fluoride. Sodium reacts with fluorine to form sodium fluoride. Write a symbol equation for this…
Answer this question and get it marked →Hydrogen iodide thermally decomposes into iodine and hydrogen. The reaction is reversible: 2HI(g) ⇌ I2(g) + H2(g) (HI colourless gas, I2 purple gas, H2 colourless gas) A sealed…
Answer this question and get it marked →May–June 2024, Paper 43
Dinitrogen tetroxide, N2O4, decomposes into nitrogen dioxide, NO2. The reaction is reversible: N2O4(g) ⇌ 2NO2(g) (N2O4 colourless gas, NO2 brown gas) A sealed gas syringe contains…
Answer this question and get it marked →May–June 2024, Paper 53
You are going to investigate the rate at which hydrogen gas is made when magnesium ribbon reacts with dilute ethanoic acid at two different temperatures. Read all of the…
Answer this question and get it marked →May–June 2024, Paper 63
A student investigates the rate at which hydrogen gas is made when magnesium ribbon reacts with dilute ethanoic acid at two different temperatures. The student does two…
Answer this question and get it marked →October–November 2024, Paper 11
Hydrogen peroxide decomposes to form water and oxygen. The equation is shown. 2H2O2(l) - 2H2O(l) + O2(g) Manganese(IV) oxide catalyses this reaction. Which statements about…
Answer this question and get it marked →Four students collect the gas produced from the reaction of calcium carbonate with dilute hydrochloric acid. Each student records the time taken to collect a volume of gas. Which…
Answer this question and get it marked →The equation for the reaction between hydrogen and oxygen is shown. 2H2(g) + O2(g) - 2H2O(g) Which statement explains why this is a redox reaction? A Both oxidation and reduction…
Answer this question and get it marked →October–November 2024, Paper 12
Which process involves a chemical change? A adding sodium chloride to water B adding magnesium to hydrochloric acid C heating solid iodine until it turns into a gas D melting lead
Answer this question and get it marked →Which two pieces of apparatus are most useful to measure the rate of a reaction in which a gas is given off? A accurate balance and gas syringe B accurate balance and thermometer…
Answer this question and get it marked →Reaction 1 and reaction 2 both produce a gas. The total volume of gas produced in each reaction is measured every minute for 10 minutes. A graph of the results is shown: curve 2…
Answer this question and get it marked →The equation for the reaction of magnesium with copper(II) oxide is shown. Mg + CuO - MgO + Cu Which word describes this reaction? A combustion B decomposition C neutralisation D…
Answer this question and get it marked →Zinc is formed when zinc oxide is heated with carbon. zinc oxide + carbon - zinc + carbon monoxide Which substance is oxidised in this reaction? A carbon B carbon monoxide C zinc…
Answer this question and get it marked →October–November 2024, Paper 13
Which process is a chemical change? A boiling water B cooking an egg C dissolving sugar D melting ice cubes
Answer this question and get it marked →A student reacts strips of zinc with dilute sulfuric acid and measures the time taken to produce 100 cm3 of hydrogen. The experiment is repeated using different conditions. The…
Answer this question and get it marked →When blue copper(II) sulfate is heated, a white solid and water are formed. The white solid turns blue and gives out heat when water is added to it. Which terms describe the blue…
Answer this question and get it marked →Which statements about a redox reaction are correct? 1 Oxidation is the gain of oxygen. 2 Both oxidation and reduction take place in a redox reaction. 3 Reduction is the gain of…
Answer this question and get it marked →October–November 2024, Paper 22
Sulfur dioxide is converted to sulfur trioxide in the Contact process. The conditions used are 450 °C and 200 kPa with a vanadium(V) oxide catalyst. Which row describes and…
Answer this question and get it marked →Hydrogen gas reacts with iodine gas to form hydrogen iodide gas in an equilibrium reaction. H2(g) + I2(g) ⇌ 2HI(g) ΔH = +26.5 kJ/mol Which changes increase the yield of HI at…
Answer this question and get it marked →The equation for the reaction of carbon with carbon dioxide is shown. C + CO2 - 2CO Which row identifies the carbon atom that is reduced and its change in oxidation number? atom…
Answer this question and get it marked →Aqueous iron(II) sulfate is added to acidified potassium manganate(VII). The purple colour disappears. Aqueous potassium iodide is added to acidified potassium dichromate(VI). A…
Answer this question and get it marked →October–November 2024, Paper 23
Which process involves a physical change only? A heating calcium carbonate strongly B burning wood C melting an ice cube D mixing an acid and a base
Answer this question and get it marked →In the Haber process, an equilibrium is established. N2(g) + 3H2(g) ⇌ 2NH3(g) The forward reaction is exothermic. Which change to the reaction conditions will move the position of…
Answer this question and get it marked →Which statement about reactants in redox reactions is correct? A An oxidising agent donates electrons, and a reducing agent accepts electrons. B When one element gains electrons,…
Answer this question and get it marked →October–November 2024, Paper 31
A student investigates the reaction of small pieces of zinc with excess dilute sulfuric acid of three different concentrations. The time taken for each reaction to finish is…
Answer this question and get it marked →October–November 2024, Paper 32
A student investigates the reaction of small pieces of calcium carbonate with excess dilute hydrochloric acid of three different concentrations. The three concentrations of acid…
Answer this question and get it marked →October–November 2024, Paper 33
A student investigates the reaction of small pieces of magnesium oxide with excess dilute hydrochloric acid of three different concentrations. The time taken for each reaction to…
Answer this question and get it marked →October–November 2024, Paper 41
When magnesium nitrate is heated strongly, magnesium oxide is formed. The equation for this reaction is: 2Mg(NO3)2 → 2MgO + 4NO2 + O2. State the change in oxidation number of…
Answer this question and get it marked →October–November 2024, Paper 43
This question is about rate of reaction and equilibrium. A student investigates the rate of decomposition of aqueous hydrogen peroxide, H2O2, using manganese(IV) oxide as a…
Answer this question and get it marked →October–November 2024, Paper 52
You are going to investigate the rate of the reaction between aqueous iron(III) nitrate and aqueous sodium thiosulfate. Read all of the instructions carefully before starting the…
Answer this question and get it marked →October–November 2024, Paper 62
A student investigates the rate of the reaction between aqueous iron(III) nitrate and aqueous sodium thiosulfate. The student does five experiments using the apparatus in Fig. 2.1…
Answer this question and get it marked →May–June 2023, Paper 31
A student investigates the reaction of small pieces of zinc of the same mass and size with three different concentrations of dilute hydrochloric acid in the presence of a…
Answer this question and get it marked →May–June 2023, Paper 32
A student investigates the reaction of different-sized pieces of calcium carbonate (large, medium, small) with dilute hydrochloric acid. All other conditions stay the same. Table…
Answer this question and get it marked →May–June 2023, Paper 33
A student investigates the reaction of magnesium with dilute hydrochloric acid at three different temperatures (20 °C, 30 °C and 40 °C). All other conditions stay the same. Table…
Answer this question and get it marked →May–June 2023, Paper 41
Oxygen is produced by the decomposition of aqueous hydrogen peroxide. Manganese(IV) oxide, MnO₂, is a catalyst for this reaction. State the meaning of the term catalyst.
Answer this question and get it marked →May–June 2023, Paper 43
Hydrogen is produced by the reaction between zinc and dilute sulfuric acid, H₂SO₄. Zn(s) + H₂SO₄(aq) → ZnSO₄(aq) + H₂(g) A student carries out an experiment using excess zinc and…
Answer this question and get it marked →May–June 2023, Paper 62
A student investigates how the rate of the reaction between aqueous iron(III) nitrate and aqueous sodium thiosulfate changes with temperature, using the apparatus in Fig. 2.1 (a…
Answer this question and get it marked →October–November 2023, Paper 31
A student investigates the reaction of large pieces of magnesium carbonate with dilute hydrochloric acid at 20 °C. The magnesium carbonate is in excess. Fig. 6.1 shows the volume…
Answer this question and get it marked →October–November 2023, Paper 32
A student investigates the reaction of large pieces of magnesium with dilute hydrochloric acid at 20 °C. The magnesium is in excess. Fig. 6.1 shows the volume of hydrogen gas…
Answer this question and get it marked →October–November 2023, Paper 33
Hydrogen peroxide, H2O2, breaks down slowly at 40 °C to produce oxygen gas and water: 2H2O2 → 2H2O + O2 A student investigates the breakdown of hydrogen peroxide at 40 °C in the…
Answer this question and get it marked →October–November 2023, Paper 41
Methane reacts with steam to produce hydrogen gas: CH4(g) + H2O(g) ⇌ CO(g) + 3H2(g) ΔH = +200 kJ / mol The reaction takes place at 1000 °C and 100 kPa pressure. The reaction is…
Answer this question and get it marked →Other IGCSE Chemistry topics
- Organic chemistry (155)
- The Periodic Table (102)
- Metals (96)
- Acids, bases and salts (84)
- Experimental techniques and chemical analysis (84)
- Stoichiometry (62)
- Chemical bonding (58)
- Chemistry of the environment (55)
- Atoms, elements and compounds (51)
- Electrochemistry (47)
- Practical skills (43)
- States of matter (42)