OCR A-Level Chemistry Periodic table, elements and physical chemistry (01), June 2018: Question 14

1 mark · Medium difficulty · Multiple Choice

Identify which statements explain why reaction rates increase as temperature increases using Maxwell-Boltzmann distribution concepts.

Practise this question

Question

Multiple choice question 14 asking which statements explain why reaction rates increase with temperature, listing three numbered statements: 1. The activation energy is less, 2. Collisions between molecules are more frequent, 3. A greater proportion of molecules have energy greater than the activation energy. Four options A, B, C, D are provided below.
Question text

14 Which statement(s) explain(s) why reaction rates increase as temperature increases?

1 The activation energy is less.

2 Collisions between molecules are more frequent.

3 A greater proportion of molecules have energy greater than the activation energy.

A 1, 2 and 3

B Only 1 and 2

C Only 2 and 3

D Only 1

Your answer [1]

Mark scheme

Show the mark scheme The mark scheme table shows the correct answer for question 14 is C, worth 1 mark.

14 C 1 AO1.1

How to answer it

Question 14: Temperature and Reaction Rates

OCR A-Level Chemistry • Multiple Choice

What this question tests

This question assesses your understanding of collision theory and Maxwell-Boltzmann distribution curves. Specifically, it tests your knowledge of how changes in temperature affect molecular kinetic energy, collision frequency, and the proportion of molecules exceeding the activation energy, while distinguishing these factors from the unchanging nature of the activation energy itself.

Question Analysis & Breakdown

✅ Correct Answer: C (Only 2 and 3)

Statement 2 and Statement 3 correctly describe the effects of increasing temperature on reactant particles.

💡 Key Knowledge

  • Activation energy (Ea) is a fixed energy barrier inherent to a specific reaction pathway. It does not change when you heat a reaction mixture.
  • Higher temperature means particles move faster, leading to more frequent collisions (Statement 2).
  • A higher temperature shifts the Maxwell-Boltzmann distribution to the right, meaning a greater proportion of molecules exceed Ea (Statement 3).

🧠 Exam Technique

Evaluate each statement individually using elimination. Instantly rule out any statement claiming activation energy changes with temperature (Statement 1). This immediately narrows your options down, saving critical time in multiple-choice sections.

❌ Common Errors

  • The Catalyst Confusion: Students often mistakenly believe that increasing temperature lowers the activation energy. Remember: only a catalyst changes the activation energy by providing an alternative pathway.
  • Ignoring collision frequency (Statement 2) while focusing solely on energy, or vice versa. Both factors contribute to the significant increase in reaction rate when temperature rises.
Examiner Commentary / Mark Scheme Note: Option C is the correct answer, worth [1] mark (AO1.1). Top-scoring candidates easily differentiated between changes to the energy of the particles versus changes to the energy barrier (activation energy).

Topics

Module 3: Periodic table and energy · 3.2 Physical chemistry

Question and mark scheme from the OCR A-Level Chemistry examination, Periodic table, elements and physical chemistry (01), June 2018. QuestionVault is an independent revision resource; questions remain the copyright of the awarding body.