Dalton's Law

Dalton's law gives the relation between the total pressure of a gas in a container and the partial pressure of its constituents.

The sum of all partial pressures in a mixture of gases is equal to the total pressure.


Note that:

The gas mixture in a closed volume does not separate. In an air-to-helium mixture, the helium does not rise to the top of the container even though it is lighter than the other gases. This is because of the thermal speed of the particles there are inter-particle collisions in the gas as well as with the container walls and therefore always a mixing process, called "diffusion"