Fick`s equations for n-k mixtures, diffusivity in n-k systems according to constitutive relations of Fick type, Maxwell equations, diffusivity in n-k systems according to consitutive relations of Macwell`s type. One-dimensional and multiple dimensional diffusion in multiple component systems, nonstationary molecular diffusion in one direction – multiple componenet systems. Convective diffusion (fundamental terms, mass transfer in different cases through the pipes, on a flat plate, with turbulent flow, interphase diffusion mass transfer, film-penetration theory, combined models, domains and application conditions of different models in specific examples, overall mass transfer coefficients, and other interphase mass transfer exchange examples, specific problems of diffusion mass transfer). Application in different industrial plants, civil engineering, medicine. Part of the course is planned to be done through student's own study research work in the field of theory and mass transfer applications. Study research work includes following the primary scientific sources, organization and conductivity of the experiments and statistical data processing, numerical simulations, and eventually writing a paper in the specific scientific field relevant to the doctoral dissertation.