The Gas Laws

These are 3 equations which describe the actual behaviour of gases, at least approximately.

There are a number of external properties that we can assign to a gas

Quantity	Pressure	Volume	Temperature	Mass	Density
Symbol	p	V	T	m
Units	N/m2 or Pa	m3	Degrees C or K	kg	kg/m3

The gas laws describe the relationships between the first 3, pressure, volume and temperature.

The Volume Law ( Charles' Law)

The volume of a fixed mass of gas, at constant pressure, is proportional to its temperature.

The Pressure Law

The pressure of a fixed mass of gas, at constant volume, is proportional to its temperature.

Boyle's law

The pressure of a fixed mass of gas, at constant temperature, is inversely proportional to its volume.

Gases obey Boyle's law very well except at high pressures. (when we force the particles too close together then intermolecular forces become more significant)

There are two types of gas:

Real gases - as described above

Ideal gases - these obey Boyle's law perfectly. They don't exist but are a very useful approximation when we devise a mathematical model for the behaviour of gases