ABSTRACT
When there is a mixture of two gases in a container, under kinetic theory the volume occupied by both gases is the same and equal to the volume of the container. Assume that the volume of the container is 1 litre and the total number of moles is 1, 80% of the molecules being N2 and 20% being O2. Note that both nitrogen and oxygen occupy the whole of the 1-litre volume. Then, applying the universal gas equation:
For nitrogen, PV=nRT
For oxygen, PV=nRT
For the mixture of gases (total 1 mol), PV=nRT
Adding together equations (1) and (2) gives:
Comparing this with equation (3) results in:
This principle of adding the component pressures to give the total gas mixture pressure is called Dalton’s law. The ratio of partial pressure is in proportion to the mole fraction of the components.
