In general, real gases behave most ideally at ,pr pressures and â¼ temperatures The behavior of real gases can be described using the van der Waals equation The values of a and b are given below for the two real gases xenon and carbon dioxide. The gas in which deviations from ideal behavior due to intermolecular forces are expected to be the largests The gas that would be expected to behave least like an ideal gas at high pressures is gas a (Latm/mol b (L/mol) Xe 4.19 5.11 102 Co: 3.59 4.27 10