States of Matter (Cambridge O Level Physics)

• The three states of matter are solids, liquids and gases

A solid, a liquid and a gas

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 incompressible

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 incompressible

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

Diagram of Changes of State

Melting and freezing are changes between solid and liquid states, boiling and condensing are changes between liquid and gas states