is defined as the hypothetical pressure of a gas that is part of a mixture of gases that occupy a certain volume and a certain temperature, if that respective gas would occupy the same volum of the mixture, at the same temperature as the mixture.

Now, the fraction on an individual gas A that is a component of an ideal gas mixture can be expressed using either the moles of this component, or its

##X_A = n_A/n_(TOTAL) = P_A/P_(TOTAL)##, where

##n_A## represents the number of moles of gas A present in the mixture; ##n_(TOTAL)## represents the total number of moles present in the mixture; ##P_A## represents A‘s partial pressure; ##P_(TOTAL)## represents the total pressure of the gas mixture.

Therefore, a gas’ partial pressure can be determined from its moles by knowing the total number of moles of the gaseous mixture and its total pressure

##P_A = n_A/N_(TOTAL) * P_(TOTAL)##