The second law and the current state of thermodynamics

The present state of equilibrium thermodynamics is analyzed from the position of using the original Clausius statement for the second law δS ≥ δQ/T when describing four directions of its applications, viz. phase states of the solid body, states of small systems (i.e., surfaces and dispersed phases), for methods of statistical physics and chemical kinetics in non-ideal systems. It is noted that the symbol ≥ simultaneously reflects both the process of striving to reach equilibrium in a closed system and this limit equilibrium state itself. The first two directions were stated by Gibbs in the limit form of the second law as the equality δS ≥ δQ/T; the same equality sign was used in the development of the third direction. The fourth direction was developed on the basis of the Gibbs chemical potential. The results of using the full statement of Clausius’s second law for each of the above directions are discussed. It is shown that for correct calculation of equilibrium characteristics one should take into account the differences in relaxation times of thermodynamic parameters and the self-consistent description of equilibrium and kinetics in molecular approaches.