Explain, using particle theory, what happens to the particles in a gas when it is cooled until it becomes a solid.

Edexcel GCSE Chemistry (1CH0) — 2.1 States of matter · Explain · 4 marks · View as Markdown

Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).

Model answer (4 marks)

As the gas cools, the particles lose kinetic energy and move more slowly.
The gas condenses as the particles come closer together to form a liquid.
The liquid freezes when the particles lose further energy and can no longer move past each other.
In the solid, the particles are arranged in a regular lattice and vibrate about fixed positions.

Examiner tips

Use the word ‘lose energy’ and ‘move more slowly’ to show understanding of kinetic energy. Show the sequence: gas → liquid → solid. Mention the regular arrangement and fixed vibration in the solid. Use correct terminology: condense, freeze, lattice.

Common mistakes

Confusing ‘cooling’ with ‘heating’ or omitting the loss of kinetic energy. Failing to state that the particles form a regular arrangement in the solid. Using vague terms like ‘come together’ without linking to condensation or freezing.

Mark scheme (4 marks)

As the gas cools, the particles lose energy / move more slowly
The gas condenses / particles come closer together to form a liquid
The liquid freezes / particles lose further energy so they can no longer move past each other
In the solid, the particles hold a regular arrangement and vibrate about fixed positions

Key terms in this question

particle theory · gas · solid