In Eq. (20), the first two terms basically indicate the enthalpy change of the system which represents the change in total
energy and can be assumed to be the system Hamiltonian. The rest of the terms indicate potential energy changes which
reduce the total entropy. Thus, for the special case of an ideal gas with some approximations, Eq. (20) represents the ratio
of difference of changes in Hamiltonian and potential energy of the system.