Solids, liquids and gases
All Sub-atomic particles and anything made from them, such as atoms and molecules, are matter. Energy and forces are not matter. consists of A general term for a small piece of matter. For example, protons, neutrons, electrons, atoms, ions or molecules. including The smallest part of an element that can exist. and A collection of two or more atoms held together by chemical bonds.. The arrangement and movement of these particles differ between the different Solid, liquid or gas. Evaporation is a change of state from liquid to gas. 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 A measure of compactness and the ratio of mass to volume. It is usually measured in kilograms per metre cubed (kg/m3) or grams per centimetre cubed (g/cm3). of a substance changes when it changes state. Its The amount of matter an object contains. Mass is measured in kilograms (kg) or grams (g). does not change. This is because its particles do not disappear - they are just rearranged and occupy a different The volume of a three-dimensional shape is a measure of the amount of space or capacity it occupies, eg an average can of fizzy drink has a volume of 330 ml..
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:
\(density = \frac{mass}{volume}\)
\(volume = \frac{mass}{density}\)
\(volume = \frac{1,000}{7,870}\)
\(= 0.127~m^3\)
Example 2
Calculate the volume of 1,000 kg of iron in the liquid state.
\(volume = \frac{1,000}{6,980}\)
\(0.143~m^3\)
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:
\(density = \frac{mass}{volume}\)
\(mass = density \times volume\)
\(mass = 1,140 \times 0.250\)
\(= 285~kg\)
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.