An ideal gas is a theoretical gas composed of many randomly moving point particles that do not interact except when they collide elastically. The ideal gas concept is useful because it obeys the ideal gas law, a simplified equation of state, and is amenable to analysis under statistical mechanics. One mole of an ideal gas has a volume of 22.7 L at STP as defined by IUPAC.

Ideal Gas Law

PV = nR_{u}T PV = mRsT Pʋ = RsT P/ ρ = RsT

m = mass of gas

V = volume of gas

M= molecular weight of gas

n = number of moles of gas = m/M

R_{u }= universal gas constant = 8.3143 J/mol.K

R_{s }= specific gas constant = R_{u}/M

ρ = density of gas = m/V