Boyle's law

Beginner

At fixed temperature, pressure is inversely proportional to volume.

Key relationPV = const

At constant temperature, PV = constant. Compressing a gas to half the volume doubles the pressure.

Worked example

1 L at 1 atm squeezed to 0.25 L: 4 atm.

Common mistake

Needs absolute pressure.

In more detail

Boyle's law states that for a fixed amount of gas at constant temperature, pressure is inversely proportional to volume, PV = constant.

Breathing relies on changes in lung volume and pressure.
Syringes show Boyle's law as the plunger is pushed in.
A syringe pushed in squeezes the air and the pressure rises, which follows Boyle's law at constant temperature.

What happens if I halve the volume?

The pressure doubles, provided the temperature and amount stay constant.

Who discovered it?

Robert Boyle, in the 1660s, from experiments with air pressure.

Why does the pressure rise when the volume falls?

The same number of molecules hit the walls more often in a smaller space, so the pressure goes up.