Mutual Diffusion Coefficient in Binary Mixtures and the Lattice Gas Model

A modification of the elementary kinetic theory of a gas mixture in terms of the lattice gas model is proposed. It is assumed that molecules of components of the mixture are spherical and close in size. In calculating the diffusion flux of molecules through a selected plane, instead of the mean thermal velocity of molecules, the mean relative velocity of molecules of components of different types is used. In this case, the flux explicitly depends on the type of component with which a molecule collided last before intersecting the selected plane. The proposed modification allows one to derive an expression for the mutual diffusion coefficient of components of a binary mixture that at low densities of the mixture (as in a rarefied gas phase), is consistent with the expression obtained in the rigorous kinetic theory of gases.