Dalton's law states that each gas in a mixture of gases exerts its own pressure, behaving as if it is the only gas present. The pressure exerted by the gas is known as partial pressure.
The partial pressure of a gas is a measure of its concentration and is expressed in kilo pascals (kPa). The Partial Pressure Formula of a gas in a mixture of gases is given by
Where PA is the partial pressure of gas A, nA is the number of moles of gas A, n is the total number of moles of gas in the mixture. fA is the mole fraction and PB is the barometric or total pressure of the mixture of gases.The pressure of the individual gases in the mixture is the partial pressure of that gas. The sum of the partial pressures is the total pressure.
The partial pressure of a gas is an idea (rather than something we can measure). We think of the total pressure of a mixture as being composed of the pressure of each gas in the mixture. The diagram below illustrates this with three different gases (show as gases A, B, and C). When by itself in a container, each gas has a specific pressure. Those are at the top and labeled as such. Then those same amounts are all three pushed into the same container again, so now the total number of moles has increased and therefore the total pressure.
Dalton's law of Partial Pressure Formula is mathematically expressed as