The volume of a spherical molecule can br estimated as V=b/4NA where b is the van der Waals parameter and NA is Avogadro's number. Justify this relationship by considering a spherical molecule of radius r, with volume V= 4/3π r3 . Determine the volume centered at the molecule that is excluded for the center of mass of a second molecule in terms of V? Apportion this volume equally among the molecules to arrive at V=b/4NA Determine the radius of a methane molecule from the value of its ven der Waals parameter b.