Rate of Reaction Exam Questions
Practice IGCSE Chemistry exam questions on rate of reaction. Covers factors affecting rate, measuring rate experimentally, interpreting rate graphs, and explaining rate changes using particle theory with mark schemes and examiner notes.
Published by IGCSEChemistry.com.my
Chemistry teaching team: K. S. Tan (15+ years teaching IGCSE Chemistry) and Ms Yash (10+ years teaching IGCSE Chemistry) and Ms Kartini (15+ years teaching IGCSE Chemistry).
Mapped to Cambridge IGCSE Chemistry 0620 (2026–2028). Last updated 2026-08-19.
These questions cover rate of reaction. Write full answers before checking.
Question 1 (4 marks, Core)
State four factors that affect the rate of a chemical reaction.
Mark scheme
Any four from:
- Temperature [1]
- Concentration of reactants (in solution) / pressure (for gases) [1]
- Surface area of solid reactants / particle size [1]
- Use of a catalyst [1]
- Light (for photochemical reactions) [1]
Examiner note: “Amount of reactant” is not the same as concentration. Adding more of a solid to excess acid does not change the rate (it changes the total amount of product). Concentration (moles per dm3) is what matters.
Question 2 (4 marks, Core)
A student investigates the reaction between marble chips (calcium carbonate) and dilute hydrochloric acid by measuring the volume of gas produced over time.
The graph shows the volume of CO2 produced: it rises steeply at first, then the curve levels off to a plateau.
(a) Why is the graph steep at the beginning? (1)
(b) Why does the graph level off? (1)
(c) How would the graph change if the experiment were repeated at a higher temperature? (2)
Mark scheme
(a) The rate is fastest at the start because the concentration of acid is highest [1]
(b) The reaction has finished / one or both reactants have been used up [1]
(c) The initial gradient would be steeper / the reaction would be faster [1], but the final volume of gas would be the same (same amount of reactant used) [1]
Examiner note: Higher temperature increases the rate but does not change the total amount of product (unless a different amount of reactant is used). The curve reaches the same height but gets there faster. Many candidates wrongly show a higher plateau.
Question 3 (3 marks, Core)
A student tests how surface area affects the rate of reaction between calcium carbonate and hydrochloric acid. She uses the same mass of marble in two experiments:
- Experiment 1: large marble chips
- Experiment 2: powdered marble
(a) Predict which experiment has the faster rate. (1)
(b) Explain your answer. (2)
Mark scheme
(a) Experiment 2 (powdered marble) [1]
(b) Powdered marble has a larger surface area [1], so more particles are exposed to the acid and there are more frequent collisions between reactant particles per unit time [1]
Examiner note: Same mass but smaller pieces = larger total surface area. More surface area means more collisions per second. The total amount of gas produced is the same in both experiments because the same mass of reactant is used.
Question 4 (3 marks, Core)
A student measures the rate of reaction between magnesium and dilute hydrochloric acid by recording the mass of the flask and contents over time on a balance.
(a) Explain why the mass decreases during the reaction. (1)
(b) State the equation for this reaction. (1)
(c) State one advantage of using the mass loss method over collecting gas in a syringe. (1)
Mark scheme
(a) Hydrogen gas is produced and escapes from the flask, so the total mass decreases [1]
(b) Mg + 2HCl → MgCl2 + H2 [1]
(c) The balance gives a continuous reading so the data can be recorded at any time / no gas is lost through leaks in the apparatus [1]
Examiner note: The mass loss method works because gas escapes. A cotton wool plug is often placed in the flask to prevent liquid splashing out while still allowing gas to escape.
Question 5 (4 marks, Supplement)
Explain, using collision theory, why increasing the concentration of a reactant increases the rate of reaction.
Mark scheme
- Increasing concentration means there are more particles of reactant per unit volume [1]
- The particles are closer together [1]
- There are more frequent collisions between reactant particles per unit time [1]
- The frequency of successful collisions increases, so the rate increases [1]
Examiner note: Not all collisions are successful — particles must collide with sufficient energy (activation energy) and correct orientation. Increasing concentration increases the total number of collisions per second, which increases the number of successful collisions per second.
Question 6 (3 marks, Core)
A student investigates how concentration affects the rate. She reacts sodium thiosulfate with hydrochloric acid and times how long it takes for a cross drawn on paper beneath the flask to disappear.
| Experiment | Concentration of Na2S2O3 (mol/dm3) | Time for cross to disappear (s) |
|---|---|---|
| 1 | 0.05 | 120 |
| 2 | 0.10 | 60 |
| 3 | 0.15 | 40 |
| 4 | 0.20 | 30 |
(a) Describe the pattern in the results. (1)
(b) Explain why the cross disappears. (1)
(c) What is the relationship between concentration and rate? (1)
Mark scheme
(a) As concentration increases, the time for the cross to disappear decreases [1]
(b) The reaction produces sulfur, which is an insoluble yellow solid/precipitate that makes the solution cloudy/opaque [1]
(c) As concentration increases, rate increases / rate is directly proportional to concentration (doubling concentration halves the time) [1]
Examiner note: Rate is inversely proportional to time: rate = 1/time. A shorter time means a faster rate. This is the “disappearing cross” experiment, one of the most commonly tested practicals.
Question 7 (3 marks, Supplement)
Explain why increasing the temperature increases the rate of a reaction. Include the concept of activation energy in your answer.
Mark scheme
- At higher temperature, particles have more kinetic energy and move faster [1]
- There are more frequent collisions [1]
- A greater proportion of collisions have energy equal to or greater than the activation energy, so there are more successful collisions per unit time [1]
Examiner note: There are two effects of temperature: (1) more collisions per second and (2) a greater proportion of those collisions are successful. Effect (2) is more significant. Simply saying “particles move faster” without linking to activation energy earns only 1-2 marks.
Question 8 (3 marks, Core)
A student adds a catalyst (manganese dioxide) to hydrogen peroxide solution. Gas is produced rapidly.
(a) Name the gas produced. (1)
(b) State how a catalyst increases the rate of reaction. (1)
(c) State one characteristic of a catalyst that distinguishes it from a reactant. (1)
Mark scheme
(a) Oxygen [1]
(b) A catalyst provides an alternative reaction pathway with lower activation energy [1]
(c) A catalyst is not used up / consumed during the reaction and can be recovered unchanged / the catalyst remains chemically unchanged at the end [1]
Examiner note: “A catalyst speeds up a reaction” is not a sufficient explanation — you must say HOW it speeds up the reaction (lower activation energy / alternative pathway). Also, a catalyst is specific to a particular reaction.
What to revise if you scored below 6
If graph interpretation was difficult (Question 2), practise sketching and labelling volume-time and mass-time graphs. If collision theory explanations were weak (Questions 5, 7), learn the chain: factor change → effect on collisions → effect on rate. Revisit the rate of reaction notes.
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