OCR A-Level Chemistry AS Breadth in chemistry (01), June 2019: Question 12

1 mark · Easy difficulty · Multiple Choice

Identify the main reason for the increase in reaction rate with increasing temperature.

Practise this question

Question

Multiple choice question 12 asking for the main reason for the increase in reaction rate with increasing temperature. Options are A: The activation energy decreases, B: The activation energy increases, C: More molecules have an energy greater than the activation energy, D: The molecules collide more frequently. A box for the answer and the mark [1] are shown at the bottom.
Question text

12 What is the main reason for the increase in reaction rate with increasing temperature?

A The activation energy decreases.

B The activation energy increases.

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

D The molecules collide more frequently.

Your answer [1]

Mark scheme

Show the mark scheme Mark scheme for question 12 showing the correct answer C, with 1 mark and assessment objective AO1.1.

12 C 1 AO1.1

How to answer it

Effect of Temperature on Reaction Rate

What this question tests

This question assesses your fundamental understanding of collision theory and Maxwell-Boltzmann distribution curves (AO1.1 Knowledge). Specifically, it tests why increasing the temperature of a reaction mixture causes a dramatic increase in reaction rate, requiring you to distinguish between particle collision frequency and particle energy.

Question 12 (Multiple Choice)

Exam Breakdown & Correct Answer

✅ Correct Answer: C

More molecules have an energy greater than or equal to the activation energy (E ≥ Eₐ).

Mark Awarded: 1 / 1 mark

💡 Key Knowledge

  • As temperature increases, the Maxwell-Boltzmann distribution curve flattens and shifts to the right.
  • A much greater proportion of molecules possess energy exceeding the activation energy (Eₐ).
  • This leads to a massive increase in the frequency of successful collisions, which is the primary driver of faster rates.

🧠 Exam Technique

Read multiple-choice options carefully for qualifiers like "main reason". While option D is technically true (molecules do move faster and collide slightly more frequently), the increase in collision frequency alone is negligible compared to the exponential surge in particles with sufficient energy to react.

❌ Common Errors

  • Choosing D: Assuming increased speed means collision frequency is the main factor. Examiners note that students often confuse general collision frequency with successful collision frequency.
  • Choosing A or B: Believing that changing the temperature alters the activation energy itself. Remember: activation energy is fixed for a given reaction unless a catalyst is added!

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 2019. QuestionVault is an independent revision resource; questions remain the copyright of the awarding body.