Changes of state

In a nutshell

Substances can change from one state of matter to another. The processes that happen when a state change occurs are: condensation, freezing, melting and evaporation.

Change of state

Definition

A change of state occurs when one state is changed to another when being heated or cooled.

Example

A liquid is changed to a solid.

Processes occurring when a state is changed

There are different changes of state that you need to know about. These are described in the table below.

process	what is happening	change in state	example
Condensation	Cooling of gases	Gas to liquid	Warm air condenses to water at a cold window.
Freezing	Cooling of liquids	Liquid to solid	Water turns to solid ice in the freezer.
Melting	Heating of solids	Solid to liquid	An ice lolly will melt if left in the sun, turning to a liquid.
Evaporation	Heating of liquids	Liquid to gas	A glass of water left in the sun will be heated and turned to water vapour.

Note: Different materials will change states at different temperatures. The temperature that water will freeze at is $0 \, \degree C$ . The temperature that water will evaporate at is $100 \, \degree C$ . This is called the boiling point of water.

Example

A material has changed state from a solid to a liquid. What type of process is happening?

The solid is being heated to form a liquid. A melting process is occurring. For example, a solid ice cube can melt and turn into liquid water.

Science; States of matter; KS2 Year 4; Changes of state