OCR A-Level Chemistry AS Breadth in chemistry (01), November 2021: Question 11

1 mark · Easy difficulty · Multiple Choice

Identify which Boltzmann distribution graph correctly shows a dotted curve at a higher temperature.

Practise this question

Question

Multiple choice question 11 showing four Boltzmann distribution graphs labeled A, B, C, and D, each plotting number of molecules against energy with a solid and a dotted curve.
Question text

11 The Boltzmann distributions below show a gas at two different temperatures.

Which Boltzmann distribution shows the dotted curve at a higher temperature?

number of

A molecules

energy

number of

B molecules

energy

number of

C molecules

energy

number of

D molecules

energy

Your answer [1]

Mark scheme

Show the mark scheme Mark scheme indicating the correct answer is A for question 11, worth 1 mark.

11 A 1 AO1.1

How to answer it

Interpreting Boltzmann Distribution Curves at Different Temperatures

What this question tests

This question assesses your understanding of the Maxwell-Boltzmann distribution and how changing temperature affects the shape and position of the curve. You must recall and apply key rules regarding the peak height, modal energy shift, and the total area under the curve.

Question 11

Exam Breakdown

✅ Correct Answer

A

Mark: 1 / 1 (AO1.1 - Demonstrate knowledge and understanding of scientific ideas)

💡 Key Knowledge

  • Higher Temperature: The curve shifts to the right, becoming broader and flatter.
  • Peak Position: The peak (most probable energy) shifts to a higher energy and a lower height.
  • Total Area: The total area under the curve must remain constant because the total number of gas molecules does not change.
  • Origin: Both curves must start at the origin (0,0) since no molecules have zero energy.

🧠 Exam Technique

  • Check the peak of the dotted curve: at a higher temperature, it must be lower down and further to the right compared to the solid curve.
  • Verify that the curves cross over cleanly. After the peak, the higher temperature curve (dotted) must stay above the lower temperature curve at high energy values, representing a greater proportion of molecules with energy exceeding the activation energy.

❌ Common Errors

  • Incorrect peak height/shift: Confusing higher temperature with a taller, narrower peak (which represents a lower temperature).
  • Failing the origin rule: Drawing curves that do not start precisely at (0,0) .
  • Changing the area: Drawing a higher temperature curve that dips below the original curve at high energies without crossing properly, implying a different number of total particles.

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), November 2021. QuestionVault is an independent revision resource; questions remain the copyright of the awarding body.