*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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