AQA A-Level Chemistry Paper 3, 2021: Question 19

1 mark · Easy difficulty · Multiple Choice

This question checks your understanding of the Maxwell–Boltzmann distribution curve, which represents how molecular energies are spread out in a gas at a certain temperature. You need to recognise key features of this curve, such as the fact that no molecules have zero energy and the curve is skewed, not symmetrical.

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Question

AQA A-Level Chemistry Paper 3, 2021: Question 19
Question text

19 Which statement about the distribution curve of molecular energies in an ideal gas at

a given temperature is correct?

[1 mark]

A There are no molecules with zero energy.

B The curve is symmetrical about the maximum.

Changing the temperature has no effect on the position of the

C

maximum.

D Most molecules have the mean energy.

Mark scheme

Show the mark scheme Mark scheme for AQA A-Level Chemistry Paper 3, 2021: Question 19

19 A 1 There are no molecules with zero energy.

How to answer it

Multiple Choice Explained: Distribution Curve of Molecular Energies

Correct Answer: A – There are no molecules with zero energy

This is a correct interpretation of the Maxwell–Boltzmann distribution. The curve starts at the origin but never touches the x-axis, meaning no molecules have exactly zero energy.

Why B is incorrect:

The curve is not symmetrical. It is skewed to the right – the distribution has a long tail showing a few molecules with very high energies. So, it is asymmetrical about the peak.

Why C is incorrect:

Changing the temperature shifts the peak of the curve. At higher temperatures, the peak moves to the right and lowers, indicating a wider spread of energies. So this statement is false.

Why D is incorrect:

Most molecules do not have the mean energy. The mean lies to the right of the peak, but the most probable energy is the energy at the peak, and fewer particles have the mean compared to the most probable energy.

Topics

Physical Chemistry · 3.1.5 Kinetics

Question and mark scheme from the AQA A-Level Chemistry examination, Paper 3, 2021. QuestionVault is an independent revision resource; questions remain the copyright of the awarding body.