Changes of State (Edexcel GCSE Physics)

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

Diagram showing the arrangement and motion of different states of matter