Consistent theory of mixtures on different levels of description

We provide an extensively discussed formulation of theory of mixtures of interacting fluids. This careful discussion leads to clarification of questions whether kinetic energy of diffusion should be defined to be part of internal energy or not, whether potential energy should be included into internal energy or not, how studying time-reversal parity of quantities determines a correct identification of entropy flux and production, or what definition of partial pressure should be adopted for non-ideal mixtures. Moreover, a generalized chemical affinity is revealed which provides natural means of coupling diffusion with chemical reactions. Finally, the theory is regarded from multilevel point of view providing a means of comparing with theories of mixtures developed within classical irreversible thermodynamics, rational (extended) thermodynamics, extended irreversible thermodynamics or GENERIC.