Learners' AlleyDesigned by Khow Willard

Rate of Reactions

Set BExam practice

Name

Time 30 minutes

Total 15 marks

Use a copy of the Periodic Table where you need one.

Multiple choice

3 marks

A student was given 4.0 g of magnesium carbonate powder and 100 cm³ of 0.1 mol/dm³ hydrochloric acid. He wants to determine the rate of reaction by measuring the change in mass of the reaction mixture. Which apparatus is not likely to be used in this experiment?

Aconical flask

Belectronic mass balance

Cstopwatch

Dtest-tube

Answer [1]

Source: 2024 CHIJ Prelim P1 Q2

Which statement about the Haber process for the manufacture of ammonia is correct?

AAt higher temperatures, the yield increases and the rate of production of ammonia is faster.

BAt higher pressure, the yield increases and the rate of production of ammonia is faster.

CIn the presence of a catalyst, the yield decreases but the rate of production of ammonia is faster.

DIn the presence of a catalyst, the yield increases and the rate of production of ammonia is faster.

Answer [1]

Source: 2025 TKGS Prelim P1 Q18

Excess magnesium powder is added to 25 cm³ of 0.10 mol/dm³ solutions of three different acids: experiment 1, methanoic acid; experiment 2, hydrochloric acid; experiment 3, sulfuric acid. Which statement is correct?

AExperiment 1 produced the smallest volume of gas.

BExperiments 1 and 2 produced the same volume of gas.

CExperiments 1 and 2 had the same speed of reaction.

DExperiments 2 and 3 had the same speed of reaction.

Answer [1]

Source: 2023 SJI Prelim P1 Q19

Structured questions

12 marks

A series of experiments was carried out to investigate the effect of concentration on the rate of reaction: BrO₃⁻(aq) + 5Br⁻(aq) + 6H⁺(aq) → 3Br₂(aq) + 3H₂O(l). The table shows the initial rates when the concentrations of the reactants were changed.

experiment	concentration of BrO₃⁻ / mol/dm³	concentration of Br⁻ / mol/dm³	concentration of H⁺ / mol/dm³	initial rate / mol/dm³/s
1	1.00	1.00	1.00	0.008
2	2.00	1.00	1.00	0.016
3	1.00	2.00	1.00	0.032
4	2.00	1.00	2.00	0.032

(a)

Use the table to describe how the concentrations of Br⁻ and H⁺ affect the initial rate of reaction.

[2]

(b)

Use ideas about collisions between particles to explain how concentration affects the initial rate of reaction.

[2]

Source: 2024 Compassvale Prelim P2 A6(a) and (b)

A student carried out two experiments with calcium carbonate and sulfuric acid: CaCO₃ + H₂SO₄ → CaSO₄ + H₂O + CO₂. The volume of carbon dioxide was measured every minute. In experiment 1, 1.20 dm³ of gas was collected in total.

experiment	moles of calcium carbonate / mol	moles of sulfuric acid / mol	concentration of sulfuric acid / mol/dm³
1	0.06	0.05	2.00
2	0.06	0.02	4.00

(a)

Describe how the graph of volume of gas against time for experiment 2 would differ from that for experiment 1.

[2]

(b)

A third experiment used 40 cm³ of 2 mol/dm³ phosphoric acid, H₃PO₄, with 6 g of calcium carbonate. Phosphoric acid is a weak acid.

(i)

Construct a balanced chemical equation for the reaction between calcium carbonate and phosphoric acid.

[1]

(ii)

Deduce the limiting reactant. Show your working.

[2]

(c)

Explain, in terms of collision theory, why using a weak acid affects the rate of reaction.

[3]

Source: 2026 ZHSS Prelim P2 A3 (adapted)