These slides present a systematic treatment of continuum thermodynamics for transport phenomena in multicomponent, two‑phase fluid systems. Starting from the balance equations for mass, momentum and energy, the material develops the entropy principle as a guiding tool to derive thermodynamically consistent models for diffusion, chemical reactions and interfacial mass transfer. Classical constitutive relations (Navier–Stokes viscosity, Fick’s law) are revisited and extended to Maxwell–Stefan multicomponent diffusion and nonlinear reaction kinetics. The closing sections examine interfacial phenomena, detailing how surface tension gradients, surfactant adsorption and Marangoni stresses couple mechanical and chemical processes at fluid interfaces.