The volume of a spherical molecule can be estimated as V = b/(4N_A), where b is the van der Waals parameter for the excluded molar volume and N_A is Avogadro’s number. Justify this relationship by considering a spherical molecule of radius r, with volume V = 4/3π r³. What is the volume centered at the molecule that is excluded for the center of mass of a second molecule in terms of V? Multiply this volume by N_A and set it equal to b. Apportion this volume equally among the molecules to arrive at V = b/(4N_A). Calculate the radius of a methane molecule from the value of its van der Waals parameter b.