Explain why a substance in the gaseous state has a much lower density than the same substance in the liquid state.

Edexcel GCSE Chemistry (1CH0) — 1.1 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)

In a gas the particles are far apart, leaving large gaps between them.
In a liquid the particles are close together, almost touching with very little space.
The same mass of the substance therefore occupies a much larger volume in the gas than in the liquid.
Density is mass divided by volume, so a larger volume for the same mass gives a lower density for the gas.

Examiner tips

  • Use the term ‘large gaps’ for gases and ‘close together’ for liquids. Show the density equation to link volume and density. Keep the answer concise, 4 short points.
  • common_mistakes
  • :
  • Confusing mass with volume or density. Using ‘smaller’ instead of ‘larger’ volume for the gas. Omitting the density formula or the link between volume and density.

Mark scheme (4 marks)

  1. In a gas, particles are far apart / have large gaps between them
  2. In a liquid, particles are close together / touching / very little space between them
  3. The same mass / number of particles occupies a much greater volume in the gas than in the liquid
  4. Density = mass ÷ volume, so a larger volume for the same mass means a lower density for the gas

Key terms in this question

density · gaseous state · liquid state

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