Avogadro's Principle

All gases at same pressure and temperature contain almost the same numbers of molecules.In other words the molar volumes of all gases are approximately the same at constant pressure and temperature.

	V=constant n

where n is the number of moles of the gas. The proportionality constant in the above equation is not dependent on the identity of the gas. Avogadro's principle becomes increasingly exact at low pressures. The molar volume of a perfect gas at STP is:

	Vm=V/n=22.414 L/mol

the same value under SATP will be:

	Vm=V/n=24.789 L/mol