OCR A-Level Chemistry Periodic table, elements and physical chemistry (01), November 2020: Question 7

1 mark · Easy difficulty · Multiple Choice

Identify the correct statement regarding a Boltzmann distribution curve at a higher temperature.

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. Below the diagram are four options (A to D) describing how the peak height and position change at a higher temperature, along with an answer box.
Question text

7 The diagram represents a Boltzmann distribution curve of molecules at a given temperature.

number of

molecules

energy

Which statement for this Boltzmann distribution curve is correct at a higher temperature?

A The peak increases in height and moves to the left.

B The peak increases in height and moves to the right.

C The peak decreases in height and moves to the left.

D The peak decreases in height and moves to the right.

Your answer [1]

Mark scheme

Show the mark scheme The mark scheme table indicates the correct answer for question 7 is D, with a mark allocation of 1.

7 D 1 1.1

How to answer it

Interpreting Boltzmann Distribution Curves at Higher Temperatures

What this question tests

This question assesses your understanding of reaction kinetics and Maxwell-Boltzmann distribution curves, specifically how an increase in temperature alters the kinetic energy distribution of gas/liquid molecules and affects the peak height and position.

Question 7 • Multiple Choice [1 Mark]

Exam Breakdown

✅ Correct Answer: D

At a higher temperature, the peak decreases in height and moves to the right. This reflects that more molecules have higher kinetic energies, spreading out the distribution curve.

💡 Key Knowledge

  • Total Area: The area under the curve represents the total number of molecules and must remain constant.
  • Mean Energy: As temperature increases, average kinetic energy increases, shifting the peak right.
  • Peak Height: Because the curve stretches out horizontally while maintaining a constant total area under the graph, the maximum peak must drop (decrease in height).

🧠 Exam Technique

  • Elimination method: Look at options involving height first. If temperature rises, particles spread out, meaning fewer share the most probable energy value (peak drops).
  • Remember the golden rule for sketching: The higher-temperature curve starts at the origin, peaks lower and to the right, and crosses underneath the lower-temperature curve to end up higher at high energies.

❌ Common Errors

  • Confusing height with total particles: Students often assume a higher temperature means a higher peak because "reactions go faster".
  • Shifting left: Incorrectly thinking heating causes molecules to slow down or compressing the graph toward the origin.
Examiner Insight: This is a classic recall and comprehension multiple-choice question. Top-level candidates instantly visualise the shifting curves where the higher temperature curve flattens and stretches towards the right-hand side of the energy axis.

Topics

Module 3: Periodic table and energy · Module 5: Physical chemistry and transition elements · 3.2 Physical chemistry · 5.1 Rates, equilibrium and pH

Question and mark scheme from the OCR A-Level Chemistry examination, Periodic table, elements and physical chemistry (01), November 2020. QuestionVault is an independent revision resource; questions remain the copyright of the awarding body.