Substances can change state, usually when they are heated or cooled. For example, liquid water turns into steam when it is heated enough, and it turns into ice when it is cooled enough.
The closeness, arrangement and motion of the particles in a substance change when it changes state. Simple diagrams of particles in a solid, liquid and a gas are shown like this:
The table summarises what happens to the particles in a substance when it gains energy, and it melts or boils (ie changes state):
|Melting||Evaporating or boiling|
|Description||Solid to liquid||Liquid to gas|
|Closeness of particles||Stay close together||Become much further apart|
|Arrangement of particles||Regular to random||Stay random|
|Motion of particles||Start to move around each other||Become able to move quickly in all directions|
Evaporation happens below the boiling point of a liquid. When the liquid reaches its boiling point, evaporation happens very quickly and the liquid boils.
The table summarises what happens to the particles in a substance when it loses energy, and it freezes or condenses (ie changes state):
|Description||Gas to liquid||Liquid to solid|
|Closeness of particles||Become much closer together||Stay close together|
|Arrangement of particles||Stay random||Random to regular|
|Motion of particles||Stop moving quickly in all directions, and can only move around each other||Stop moving around each other, and only vibrate on the spot|
The particles in a substance stay the same when it changes state - only their closeness, arrangement or motion change. This means that the mass of the substance stays the same. For example, 10 g of water boils to form 10 g of steam, or freezes to form 10 g of ice. This is called conservation of mass.