C.A. COULSON’s scientific contributions

... Clausius' formulation of the second law of thermodynamics contained a way to consider the transfer of nonmechanical energy in the first law of thermodynamics. This formulation is rather complex to understand because it simultaneously contains both the process of development toward equilibrium in a closed system and the limiting equilibrium state [25,111,112]. The mathematical formulation of the combined equation of thermodynamics is dU ≤ TdS − PdV, where U is the internal energy, P is pressure, and V is the volume of the system; the sign of the equality corresponds to the equilibrium. ...

Reference:

Molecular Modeling of Supercritical Processes and the Lattice—Gas Model