Chemical reactions — IGCSE Science - Combined (0653) questions by topic
Distinguishing chemical from physical change and explaining rate of reaction from graphs and tables define this topic: identifying which listed process is a chemical change, and linking collision frequency to temperature or concentration on a hydrogen-gas graph. Identify, explain and describe lead the command words, and explain wants collision theory reasoning rather than a repeated trend.
With 15 real questions from 2023 to 2025 papers and marks from 1 to 9, single multiple-choice items sit alongside short rate-of-reaction explanations. Submitting each explanation for instant marking is useful here, since it catches quickly when a rate difference is attributed only to reactivity rather than to the actual mechanism of collision frequency the mark scheme rewards.
What examiners look for
- A recurring error picks the highest-concentration experiment instead of the highest-temperature one when identifying the fastest reaction.
- Reports criticise answers stating that higher reactivity simply means more gas is produced, since this repeats the table data instead of linking reactivity to rate.
- Rate differences with concentration should be explained through collision frequency, not just restated as a faster reaction.
- Strong answers link the number of collisions exceeding the activation energy to temperature, and discuss the relative reactivities of copper and hydrogen to explain why copper produces no gas with dilute acid.
May–June 2025, Paper 11
The evaporation of ethanol is an example of a ......1...... change because ......2...... . Which words complete gaps 1 and 2? 1 2 --- --- --- A chemical a gas is produced B…
Answer this question and get it marked →Magnesium is added to excess dilute hydrochloric acid. The equation for the reaction is shown. Mg(s) + 2HCl(aq) - MgCl2(aq) + H2(g) Which change in conditions increases the rate…
Answer this question and get it marked →Which description explains why a reaction involves reduction? A mass decreases B oxygen is lost C pH decreases D temperature decreases
Answer this question and get it marked →May–June 2025, Paper 12
Which statement indicates that a chemical change occurs? A Energy is absorbed. B There is a change in colour. C There is a change of state. D There is no change in mass.
Answer this question and get it marked →Dilute sulfuric acid reacts with excess zinc granules. Hydrogen gas forms. Line X on the graph shows the results. The graph plots volume of hydrogen collected against time: line X…
Answer this question and get it marked →Which statement describes what happens during reduction? A An element gains oxygen. B A compound gains oxygen. C A compound loses oxygen. D A mixture of elements loses oxygen.
Answer this question and get it marked →May–June 2025, Paper 13
Which process results in a chemical change? A Heat liquid water to form steam. B Mix powdered carbon and iron filings. C Melt iron filings. D Heat sulfur in air to make sulfur…
Answer this question and get it marked →May–June 2025, Paper 21
Which statement about catalysts is correct? A Catalysts decrease the rate of reaction. B Catalysts increase the concentration of reactants. C Catalysts are unchanged at the end of…
Answer this question and get it marked →Which processes involve a chemical change? 1 cracking of an alkane 2 polymerisation of ethene 3 corrosion of iron A 1, 2 and 3 B 1 and 2 only C 1 and 3 only D 2 and 3 only
Answer this question and get it marked →May–June 2025, Paper 22
Which statement explains why the rate of a reaction is greater at a higher temperature? A The activation energy is higher. B More colliding particles have the minimum energy to…
Answer this question and get it marked →May–June 2025, Paper 23
Calcium carbonate pieces react with dilute hydrochloric acid. Which change decreases the rate of the reaction? A Add a catalyst. B Decrease the temperature. C Increase the…
Answer this question and get it marked →May–June 2024, Paper 31
Solid zinc and dilute sulfuric acid react to form zinc sulfate and hydrogen gas: Zn + H2SO4 → ZnSO4 + H2. A student measures and controls the temperature, the volume and the…
Answer this question and get it marked →May–June 2024, Paper 32
A student investigates the reaction of magnesium with excess dilute hydrochloric acid using the apparatus shown in Fig. 2.1. The equation for the reaction is: Mg + 2HCl → MgCl2 +…
Answer this question and get it marked →May–June 2023, Paper 42
A student does five experiments on the reaction between magnesium and dilute hydrochloric acid, measuring the volume of gas given off in the first 10 s (Fig. 5.1, gas syringe).…
Answer this question and get it marked →October–November 2023, Paper 41
A student does five experiments to investigate the reaction between zinc granules and dilute hydrochloric acid. In each experiment the student measures the volume of gas produced…
Answer this question and get it marked →Other IGCSE Science - Combined topics
- Practical skills (96)
- Motion, forces and energy (53)
- Electricity and magnetism (38)
- Waves (32)
- Human nutrition (23)
- Acids, bases and salts (22)
- Organisms and their environment (21)
- Organic chemistry (21)
- Reproduction (20)
- Thermal physics (20)
- Plant nutrition (19)
- The Periodic Table (18)