AQA GCSE Physics

Revision Notes

3.1.4 Changes of State

Changes of State

  • When a substance changes state, the number of molecules in that substance doesn’t change and so neither does its mass
    • The only thing that changes is its energy
  • Unlike chemical changes, changes of state (a type of physical change) are reversible
  • In a solid:
    • The molecules are very close together and arranged in a regular pattern
    • The molecules vibrate about fixed positions
  • In a liquid:
    • The molecules are still close together (no gaps) but are no longer arranged in a regular pattern
    • The molecules are able to slide past each other
  • In a gas:
    • The molecules are widely separated – about 10 times further apart in each direction
    • The molecules move about randomly at high speeds
  • There are six changes of state that can occur between solids, liquids and gases:
    • Melting – When a solid turns into a liquid (e.g. ice to water)
    • Boiling – When a liquid turns into a gas (evaporating)
    • Condensing – When a gas turns into a liquid
    • Freezing – When a liquid turns into a solid
    • Subliming -When a solid turns into a gas

Solids liquids gases, IGCSE & GCSE Physics revision notes

Diagram showing the arrangement and motion of different states of matter 

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