GCSE Combined Science revision · Physics: energy, electricity, particles and atoms

Density and changes of state

The idea

Density ρ = m ÷ V, measured in kg/m³ (or g/cm³). The particle model explains density: solids are usually densest because particles are closely packed; gases are least dense. When a substance changes state, its mass is conserved. Changes of state are physical changes: the material recovers its original properties if the change is reversed.

Find mass and volume in matching units.
Use ρ = m ÷ V.
For an irregular object, find the volume by displacement of water.

Watch out Changes of state are physical, not chemical: the substance is the same, just rearranged.

See it worked

Worked example

A block has a mass of 540 g and a volume of 200 cm³. Calculate its density.

ρ = m ÷ V = 540 ÷ 200.
= 2.7 g/cm³.

Answer 2.7 g/cm³

Your turn

Question 1Calculator allowed2 marks

A stone of mass 150 g is lowered into a measuring cylinder and the water level rises from 40 cm³ to 100 cm³. What is its density in g/cm³?

Question 2Calculator allowed1 mark

Why are gases much less dense than solids?

Question 3Calculator allowed1 mark

When ice melts, its mass:

In past papers

42 official questions in 36 papers since 2018. The latest:

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