 The other term that is introduced in the van der Waals equation, formula_4, describes a weak attractive force among molecules (known as the van der Waals force), which increases when "n" increases or "V" decreases and molecules become more crowded together.The van der Waals constant "b" volume can be used to calculate the van der Waals volume of an atom or molecule with experimental data derived from measurements on gases.For helium, "b" = 23.7 cm/mol.