The actual volume occupied by gas molecules is very small compared to the volume the gas occupies.

A gas consists of small particles (atoms or molecules) that move randomly with high velocities

The attractive forces between particles of a gas are usually very small.

Kinetic Molecular Theory of Gases

The average kinetic energy of gas molecules is proportional to the Kelvin temperature.

Kinetic Molecular Theory of Gases

​Gas particles are in constant motion, moving rapidly in straight paths

Pressure, P

When gas particles strike the walls of their container, they exert pressure.

If the gas is heated, the molecules move faster and strike the walls of the container more often with increased force, increasing the pressure.

the pressure exerted by a column of air from the top of the atmosphere to the surface of the Earth.


~1 atmosphere (atm) at sea level.

Atmospheric Pressure