Rates of reaction test answers and mark scheme for GCSE chemistry (free PDF download)

The questions are on the rates of reaction test. Take it under real conditions before reading the mark scheme.

Quick answer: The rate of reaction is how quickly reactants are used up or products form, measured as amount per unit time. This mark scheme gives the model answers and the marks for the 8 questions of the Chemistry 9-10 test on rates of reaction, from concentration and collisions to flour dust, with the equivalent answers to accept.

Rates of reaction test answers and mark scheme for GCSE chemistry (free PDF download)

Award the marks as shown. Explanations need to name the particle idea, not only the factor, to gain full credit. Accept correct alternative wording, and give credit for a correct method when an earlier number was wrong.

Level: Chemistry grades 9-10 (GCSE · IGCSE · O Level · Class 9-10) · Curriculum: HS-PS1-5

Contents

Question 1 Concentration and collisions (3 marks)

In the stronger acid there are more acid particles in each cm³. The zinc is hit more often, so there are more successful collisions each second. (2 marks)
It stays the same, because the same amount of zinc reacts. (1 mark)

Marking: (a) 1 mark for more particles per volume, 1 for more frequent collisions; (b) 1 mark.

Question 2 Two experiments (3 marks)

A, because its line is steeper. (1 mark)
The same amount of the limiting reactant is used, so the same amount of gas forms. (1 mark)
B used a lower temperature, a lower concentration or larger lumps instead of powder. (1 mark)

Marking: 1 mark each; accept any valid factor in (c).

Question 3 Mean rate (2 marks)

Rate = 54 ÷ 45 = 1.2 cm³/s.

Marking: 1 mark for the formula, 1 for the value with unit.

Question 4 Surface area (3 marks)

Before: 6 × 16 = 96 cm². After: each small cube 6 × 4 = 24 cm², and 8 × 24 = 192 cm². (2 marks)
The rate increases because more surface is exposed to the acid. (1 mark)

Marking: 1 mark for each area; 1 mark for the effect.

Question 5 Temperature (3 marks)

The particles move faster and collide more often; more particles have at least the activation energy. (2 marks)
The increase in the fraction of particles with enough energy. (1 mark)

Marking: 1 mark for each reason; 1 mark for the larger effect.

Question 6 Catalysts (2 marks)

A catalyst provides an alternative pathway with a lower activation energy, so more collisions are successful. It takes part in the reaction but is regenerated at the end, so it is not used up. Lower activation energy.

Marking: 1 mark for alternative pathway or lower activation energy, 1 mark for not used up.

Question 7 Doubling rule (2 marks)

Two rises of 10 °C make the rate 2 × 2 = 4 times faster, so the time is 120 ÷ 4 = 30 s.

Marking: 1 mark for the factor of 4, 1 mark for the time.

Question 8 Flour dust (2 marks)

Dust has a very large surface area exposed to oxygen, so there are many more collisions per second. The energy released heats the neighbouring dust and the reaction spreads almost instantly. Large surface area gives a very high rate.

Marking: 1 mark for large surface area, 1 mark for more frequent collisions or rapid spread.

← Back to the rates of reaction test

What is the rate of reaction? — Amount of product formed or reactant used per time

What does collision theory say? — Particles must collide with enough energy to react

Name the four main factors that change rate. — Temperature, concentration, surface area, catalyst

Why does powder react faster than lumps? — Larger surface area, more collisions

What is a catalyst? — A substance that speeds up a reaction and is not used up

How does a catalyst work? — Lowers the activation energy

Unit of rate for a gas volume? — cm³/s

Effect of raising pressure on a gas reaction? — More particles per volume, higher rate

What is shown by the gradient of a graph? — The rate of reaction

Why does the curve flatten? — Reactants have been used up