The real utility of the General or Ideal Gas Law is in making calculations involving amounts of gases nearly as routine as those involving solids, liquids and solutions.

For solids and liquids, mass and/or volume can easily be used to express amounts and both can readily be converted to moles. With solutions we have Molarity. But gases present a problem because the amounts of gases typically used in laboratory work are small and their measured masses are subject to buoyancy effects which can be significant. Moreover, several conditions must be known in order to determine the amount of a gas present (e.g., temperature and pressure). The General Gas Law allows all of this to be done in one step. And that means stoichiometry can be extended to systems involving gases.

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