We can learn more about the properties of gases using the kinetic theory and the gas laws.

Pressure on a gas

If a gas is sealed up in a container (like the gas in a party balloon), the walls of that container experience a pressure on its walls.

The container experiences a pressure because the particles of the gas constantly hit its walls.

Increasing pressure

The pressure of a gas can be increased in the following ways:

  • Increasing the volume of the gas
  • Decreasing the volume of the container
  • Heating up the gas in the container/ increasing its temperature

All these methods increase the pressure of a gas by increasing the kinetic energy of its particles.

Boyle’s law

‘Increasing the pressure on a gas decreases its volume’

The preceding hypothesis was investigated by an English physicist and chemist- Robert Boyle. Boyle is also known to produce a mathematical relationship between the pressure  and volume  of a gas.

The relationship that Boyle found can be stated as:

This relationship can also be written in a much more useful form that needs to be used in your IGCSE physics examination:

The preceding relationship can also be represented in words:

‘The volume of a fixed mass of gas is inversely proportional to its pressure, provided that its temperature remains constant

The preceding statement is known as the Boyle’s law.

The temperature needs to remain the same as a change in temperature will result in a change in volume (as the gas would expand/contract.)

Exam tip! Remember to use the same units for and while making calculations  related to Boyle’s law.


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