The Ehrenfest theorem and gas transport properties

It is shown that the momentum transfer theorem implies a rough correlation of the diffusion cross section with the slope of the intermolecular potential energy. This is a particular case of the collision Ehrenfest theorem which can be applied in like manner to all of the collision cross sections arising in kinetic theory, thus allowing a qualitative discussion of their dependence on the potential. As an example, relative to the diffusion cross section the viscosity has an increased sensitivity to the curvature of the potential.