In general, real gases behave most ideally at temperatures and pressures.

The behavior of real gases can be described using the van der Waals equation [P + (n2a/V2)](V-nb) = nRT

The values of a and b are given below for the two real gases methane and oxygen.

The gas in which deviations from ideal behavior due to intermolecular forces are expected to be the largest is .

The gas that would be expected to behave most like an ideal gas at high pressures is .

gas a (L2atm/mol2) b (L/mol)

CH4 2.25 4.28×10-2

O2 1.36 3.18×10-2