Free Rate of reaction questions for IGCSE Chemistry (0620), part of Chemical reactions. Each question has the answer and the marking points an examiner would look for.
Generate a full Rate of Reaction worksheet →All Chemical reactions questionsWhich change does not increase the rate of reaction between magnesium and dilute acid?
Answer: C
How does a catalyst increase the rate of reaction?
Answer: D
Explain, using collision theory, the effect of each change on the rate of reaction.
Increasing the temperature.
Adding a catalyst.
| Part | Answer and marking points | Marks |
|---|---|---|
| (a) | more energy, more frequent and more successful collisions particles have more kinetic energy and move faster B1 collide more frequently B1 a greater proportion of collisions have energy ≥ activation energy B1 | 3 |
| (b) | lower activation energy a catalyst provides an alternative pathway with a lower activation energy B1 so more collisions are successful B1 | 2 |
Magnesium ribbon reacts with excess dilute hydrochloric acid. The volume of hydrogen is measured every minute.
| time / min | 0 | 1 | 2 | 3 | 4 | 5 | 6 |
|---|---|---|---|---|---|---|---|
| volume of hydrogen / cm³ | 0 | 54 | 84 | 100 | 109 | 114 | 117 |
Calculate the average rate of reaction during the first two minutes, in cm³/min.
Describe and explain how the rate changes during the experiment. Use ideas about particles.
The experiment is repeated at a higher temperature with all other conditions the same. State the effect on the initial rate and on the total volume of hydrogen. Explain both answers.
Suggest why the total volume of hydrogen does not increase after a certain time.
| Part | Answer and marking points | Marks |
|---|---|---|
| (a) | 42 cm³/min 84 ÷ 2 M1 42 A1 | 2 |
| (b) | Rate decreases: the concentration of acid falls and the surface area of magnesium decreases, so there are fewer collisions per second rate decreases (as time goes on) B1 concentration of acid / amount of magnesium decreases B1 fewer (successful) collisions per second B1 | 3 |
| (c) | Initial rate is higher because particles move faster and have more energy, so more frequent and more successful collisions; total volume is the same because the same mass of magnesium (limiting) is used rate increases B1 particles have more (kinetic) energy, more frequent / more energetic collisions B1 total volume unchanged B1 same amount of the limiting reactant (magnesium) B1 | 4 |
| (d) | All the magnesium has reacted all the magnesium has been used up B1 | 1 |
Calcium carbonate reacts with excess dilute hydrochloric acid. Experiment A uses large lumps; experiment B uses the same mass of powder. Fig. 5.1 shows the results.
Which experiment has the faster initial rate? Explain using collision theory.
Explain why both experiments produce the same final volume of gas.
Name the gas produced and give a test for it.
| Part | Answer and marking points | Marks |
|---|---|---|
| (a) | B: powder has larger surface area, more particles exposed, so more frequent collisions B B1 Larger surface area B1 More frequent collisions (per second) B1 | 3 |
| (b) | Same mass (moles) of calcium carbonate, the limiting reactant Same amount of CaCO3 / limiting reactant B1 | 1 |
| (c) | Carbon dioxide; turns limewater milky carbon dioxide B1 limewater turns milky / cloudy B1 | 2 |
A student investigates the effect of concentration on the reaction between magnesium ribbon and hydrochloric acid.
State two variables that must be kept constant.
Explain, using collision theory, why a more concentrated acid reacts faster.
Suggest one hazard and a precaution.
| Part | Answer and marking points | Marks |
|---|---|---|
| (a) | temperature; length/mass of Mg; volume of acid Any 2 of: temperature; length/mass of magnesium; volume of acid B2 | 2 |
| (b) | more particles per volume, more frequent collisions more acid particles in the same volume B1 more frequent collisions B1 | 2 |
| (c) | acid irritant; eye protection hydrochloric acid is corrosive/irritant B1 wear eye protection B1 | 2 |
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Meet Riyaz →Original Cambridge-style practice questions written for mentorriyaz.in. These are not Cambridge past paper questions, and this site is not affiliated with or endorsed by Cambridge University Press & Assessment. Updated 2026-11-04. Paper generator · mentorriyaz.in