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Temperature changes and energy - EdexcelStates of matter

Changes in a material's temperature or state of matter are caused by changes to the internal energy. The energy required by different materials depends on their 'heat capacity' and 'latent heat'.

Part of Physics (Single Science)The particle model

States of matter

In everyday life, there are three of matter 鈥 solids, liquids and gases. The differences between the three states are due to the arrangement and spacing of the particles and their motion.

Solids, liquids and gasses

Particles in a solid, tightly packed together in order.

The particles in a solid:

  • are in a regular arrangement
  • vibrate about a fixed position
  • sit very closely together
Particles in a liquid, packed together, very fluid.

The particles in a liquid:

  • are randomly arranged
  • move around each other
  • sit close together
Particles in a gas, random order, not together.

The particles in a gas:

  • are randomly arranged
  • move quickly in all directions
  • are far apart

Changing state

Adding or removing from a material can change the state. Heating a solid material will cause it to from a solid to a liquid. Continued heating will cause the liquid to boil or to form a gas. In some instances, a solid material being heated can go straight to being a gas without being a liquid - this process is called .

Cooling a gas will cause it to from a gas to a liquid and cooling it further will cause it to then from a liquid to a solid.

Flow chart showing processes between solid, liquid and gas, using water, ice and steam from a kettle as an example. Labels show all the processes in how one can change to another.
Figure caption,
Water changing state

Boiling is an active process. People actively apply energy to a liquid to turn it into a gas using a heater such as a kettle.

on the other hand is a process. The liquid will slowly absorb energy from the surrounding area so that some of its particles will gain enough energy to escape the liquid.

Throughout all of these changes the number of particles does not change, but their spacing and arrangement does. As a result the total mass has not changed. It does not matter if a substance melts, freezes, boils, evaporates, condenses or sublimates: the mass does not change.

These changes in state are called physical changes because the process can be reversed (eg cooling instead of heating). This is different to the changes seen in a chemical reaction, which cannot be reversed so easily.