# Solids, liquids and gases

All consists of including and . The arrangement and movement of these particles differ between the different of matter:

• solids - particles are close together in a regular structure and vibrate about fixed positions
• liquids - particles are close together but free to move past each other randomly
• gases - particles are far apart and move randomly in all directions

The of a substance changes when it changes state. Its does not change. This is because its particles do not disappear - they are just rearranged and occupy a different .

## Solids and liquids

A substance melts when it changes from the solid state to the liquid state. Its particles remain close together, so there is usually a relatively small change in volume and density. For example:

• the density of solid iron is about 7,870 kg/m3
• the density of liquid iron is about 6,980 kg/m3

### Example 1

Calculate the volume of 1,000 kg of iron in the solid state.

Rearrange the equation:

### Example 2

Calculate the volume of 1,000 kg of iron in the liquid state.

Iron in the liquid state occupies a greater volume than the same mass of iron in the solid state. Iron atoms are further apart in liquid iron.

## Liquids and gases

A substance evaporates or boils when it changes from the liquid state to the gas state. Its particles move so there is a large change in volume and density. For example:

• the density of liquid oxygen is about 1,140 kg/m3
• the density of gaseous oxygen is about 1.42 kg/m3

### Example 3

Calculate the mass of oxygen that occupies 0.250 m3 in the liquid state.

Rearrange the equation:

### Example 4

Calculate the mass of oxygen that occupies 0.250 m3 in the gas state.

mass = density × volume

= 1.42 × 0.250

= 0.355 kg

Oxygen in the gas state has a much smaller mass than the same volume of oxygen in the liquid state. Oxygen molecules are much further apart in gaseous oxygen, so they occupy a much larger volume.