States of Matter (Cambridge (CIE) IGCSE Physics)
Revision Note
Written by: Lindsay Gilmour
Reviewed by: Caroline Carroll
Properties of solids, liquids & gases
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
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
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.
Examiner Tips and Tricks
It is very useful to think about water when learning the changes of state, because we are all used to the idea that solid water (ice) melts to become liquid water (water!) and boils to become gaseous water (water vapour).
However do remember that all substances undergo the same changes between the three states, but at different temperatures. So while water will help you to remember the names, don't refer to water in your answers unless it has been specified.
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