States of Matter (CIE IGCSE Physics: Co-ordinated Sciences (Double Award))

The three states of matter

The three states of matter in terms of shape and volume

Solids

• Solids have a definite shape and a definite volume
  • Solids cannot flow and are not compressible

Liquids

• Liquids have no definite shape but do have a definite volume
  • Liquids are able to flow to take the shape of a container but they are not compressible

Gases

• Gases have no definite shape and no fixed volume
  • Gases can flow to take the shape of their container and are highly compressible

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
• Changes of state are physical changes and so they are reversible

Melting & freezing

• Melting occurs when a solid turns into a liquid (e.g. ice to water)
• Freezing occurs when a liquid turns into a solid

Boiling & condensing

• Boiling occurs when a liquid turns into a gas
  • This is also called evaporating
• Condensing occurs when a gas turns into a liquid
  
  

You need to know these four processes only, and the states at which they start and end.