OCR A-Level Chemistry AS Breadth in chemistry (01), June 2023: Question 13

1 mark · Easy difficulty · Multiple Choice

Identify the effect of a catalyst on the activation energy using a Boltzmann distribution curve.

Practise this question

Question

A multiple-choice question showing a Boltzmann distribution curve with 'number of molecules' on the y-axis and 'energy' on the x-axis, with activation energy labeled E_a. Below the graph, four options A, B, C, and D describe the effect of a catalysed reaction, with an answer box at the bottom left.
Question text

13 The Boltzmann distribution showing the activation energy, Ea, for an uncatalysed reaction is

shown below.

number of

molecules

Ea

energy

What is the difference for the catalysed reaction?

A The activation energy shifts to the left.

B The activation energy shifts to the right.

C The curve flattens.

D The curve shifts to the right.

Your answer [1]

Mark scheme

Show the mark scheme The mark scheme table shows question 13 has the correct answer A, worth 1 mark, classified under assessment objective AO1.1.

13 A 1 AO1.1

How to answer it

Interpreting Boltzmann Distributions with Catalysts

What this question tests

This question assesses your understanding of collision theory and how a catalyst affects the activation energy (Ea) on a Boltzmann distribution curve (AO1.1 - Knowledge and Understanding).

Question 13

Exam Breakdown & Solutions

✅ Correct Answer

A – The activation energy shifts to the left.

Mark Awarded: 1 / 1 mark

💡 Key Knowledge

  • A catalyst provides an alternative reaction pathway with a lower activation energy (Ea).
  • On a graph where energy increases from left to right, a lower activation energy value is positioned further to the left of the original Ea line.
  • Adding a catalyst does not change the shape or peak of the Boltzmann distribution curve itself (unlike increasing temperature).

🧠 Exam Technique

  • Always check the x-axis label. Here, energy increases to the right. Therefore, "lower energy" means moving left.
  • Eliminate distractors: Option C and D describe the effect of changing temperature or adding more particles, not a catalyst.

❌ Common Errors

  • Confusing the effect of a catalyst with temperature changes. Increasing temperature shifts the peak right and flattens the curve, whereas a catalyst only repositions the Ea marker line to the left.
  • Assuming a catalyst changes the kinetic energy of the individual molecules. It doesn't—it simply lowers the threshold energy needed for successful collisions.

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 2023. QuestionVault is an independent revision resource; questions remain the copyright of the awarding body.