Edexcel A-Level Chemistry AS Paper 2, June 2023: Question 1

2 marks · Medium difficulty · Practical Techniques and Data Analysis

Add another line on the Maxwell-Boltzmann distribution graph to represent the same reaction with the same number of particles at a higher temperature.

Practise this question

Question

An exam question asking to draw a higher temperature Maxwell-Boltzmann distribution curve on an existing graph. The graph has axes labeled 'Number of particles with energy, E' on the vertical axis and 'Energy, E' on the horizontal axis, showing a standard unsymmetrical bell-shaped curve starting at the origin.
Question text

1 This question is about collision theory.

The Maxwell‑Boltzmann distribution of molecular energies for a reaction at a

particular temperature is shown in the graph.

Add another line on the graph to represent the same reaction with the same number

of particles at a higher temperature.

Number of

particles with

energy, E

Energy, E

(Total for Question 1 = 2 marks)

Mark scheme

Show the mark scheme The mark scheme awards two marks: one mark for a curve with a lower peak that starts at the origin, and a second mark for a curve positioned to the right of the original curve that approaches the x-axis asymptotically without crossing multiple times.

Question

Acceptable Answer Additional Guidance Mark

Number

1 An answer that makes reference to the following points: (2)

• peak height of curve is lower Do not award lines which cross over the existing line more

and than once

starts at origin (1)

• to the right of the existing curve

and Ignore any lines indicating activation energy even if

approaches x-axis asymptotically (1) incorrect

(Total for Question 1 = 2 marks)

How to answer it

Maxwell-Boltzmann Distribution Curves

What this question tests

This question assesses your understanding of collision theory and kinetic energy distribution among particles. You need to know how changing temperature affects the shape and position of a Maxwell-Boltzmann distribution curve while keeping the total number of particles constant.

Question 1 (Total: 2 Marks)

Drawing a Higher Temperature Maxwell-Boltzmann Curve

✅ Correct Answer / Mark Scheme Breakdown

  • Mark 1: The peak of the new curve must be lower than the original peak, and the curve must start at the origin (0,0).
  • Mark 2: The peak and body of the new curve must be shifted to the right of the existing curve, and the right-hand tail must approach the x-axis asymptotically without touching or crossing it incorrectly.

💡 Key Knowledge

  • Average Energy: At a higher temperature, particles have more kinetic energy, shifting the distribution to the right.
  • Constant Area: Because the number of particles is the same, the total area under the curve must remain constant. To make up for the curve being flatter/shifted right, the peak must drop lower.

🧠 Exam Technique

  • Draw your curve smoothly in a single, confident pencil line.
  • Make sure your line intersects the origin explicitly. Examiners heavily penalize curves that float above zero or start on the y-axis.
  • Ensure the new curve crosses the original curve only once on the downward slope.

❌ Common Errors

  • Drawing a higher temperature curve that is taller and narrower (confusing temperature with concentration or activation energy changes).
  • Failing to start the curve at the origin (0,0).
  • Allowing the new curve to cross the original curve multiple times.
  • Bringing the tail of the curve down to touch or drop below the x-axis prematurely.
Examiner Note: Top-level responses demonstrate precise control over curve symmetry and ensure the peak clearly drops while shifting right, maintaining the visual illusion of constant area under the graph.

Topics

Physical Chemistry · Topic 9: Kinetics I

Question and mark scheme from the Edexcel A-Level Chemistry examination, AS Paper 2, June 2023. QuestionVault is an independent revision resource; questions remain the copyright of the awarding body.