Explain, using particle theory, why a liquid can be poured into a container and changes shape to fill the bottom of that container, whilst keeping the same volume.

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)

Particles in a liquid are close together and almost touch each other. They can move past one another because the forces between them are not as strong as in a solid. This movement allows the liquid to flow and take the shape of the container, so it fills the bottom. The volume stays the same because the number of particles and the distances between them do not change.

Examiner tips

  • Use the phrase "particles can move past one another" to show understanding of fluidity.
  • Mention that the liquid takes the shape of the container to justify the change in shape.
  • Explain that volume remains constant because the number of particles and their spacing stay the same.
  • Keep the answer concise and use the exact terminology from the mark scheme.

Common mistakes

  • Writing that particles are far apart or that they are fixed in place.
  • Forgetting to state that the liquid takes the shape of the container.
  • Claiming that the volume changes when it actually does not.

Mark scheme (4 marks)

  1. Particles in a liquid are close together / touching
  2. Particles in a liquid can move past each other / are free to move
  3. This movement allows the liquid to take the shape of the container / flow to fill the bottom
  4. Volume stays the same because the number of particles / the distance between particles does not change

Key terms in this question

particle theory · liquid · volume

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