OCR A-Level Chemistry AS Breadth in chemistry (01), June 2024: Question 12

1 mark · Easy difficulty · Multiple Choice

Identify the correct statement explaining why heating a mixture of gases in a closed container increases the reaction rate.

Practise this question

Question

Multiple-choice question 12 asking why a gas mixture heated in a closed container increases in reaction rate, with options A to D including statements about activation energy, molecular energy, and concentration.
Question text

12 A mixture of gases is heated in a closed container. The reaction rate increases.

Which statement explains why the rate increases?

A More molecules have an energy greater than the activation energy.

B The activation energy decreases.

C The activation energy increases.

D The concentration of the gases increases.

Your answer [1]

Mark scheme

Show the mark scheme Mark scheme indicating the correct answer for question 12 is A, worth 1 mark.

12 A 1

How to answer it

Effect of Temperature on Reaction Rate

What this question tests

This question assesses your understanding of Maxwell-Boltzmann distribution curves and how changing temperature affects the kinetic energy of gas molecules and collision theory, specifically regarding the proportion of molecules exceeding the activation energy.

Question 12

Multiple Choice Analysis

✅ Correct Answer: A

When a gas mixture is heated, the average kinetic energy of the molecules increases. This shifts the Maxwell-Boltzmann distribution curve to the right and flattens it, meaning a greater proportion of molecules now possess energy greater than or equal to the activation energy ( Ea ).

💡 Key Knowledge

  • Temperature rise: Increases kinetic energy of particles, leading to more frequent and more energetic collisions.
  • Activation energy: Heating does not change the activation energy itself (eliminating options B and C).
  • Concentration: The container is closed and heated, meaning volume is constant, so concentration does not change (eliminating option D).

🧠 Exam Technique

For multiple-choice questions involving Maxwell-Boltzmann curves or collision theory, quickly eliminate options that suggest catalysts or concentration changes are at play. Always link "heating" directly to kinetic energy and the area under the curve beyond Ea .

❌ Common Errors

Students often incorrectly assume that heating a gas increases its concentration (confusing temperature changes with adding more substance or decreasing volume) or mistakenly believe that temperature lowers the activation energy.

Mark Allocation: [1 mark] awarded for selecting option A.

Topics

Module 3: Periodic table and energy · 3.2 Physical chemistry

Question and mark scheme from the OCR A-Level Chemistry examination, AS Breadth in chemistry (01), June 2024. QuestionVault is an independent revision resource; questions remain the copyright of the awarding body.