This article involves a unified treatment of equilibrium thermodynamics of the chemical reaction coupled with other interfacial (phase boundary) reactions. The modified (restrictive) chemical potential ${mu}_k^+$, such as electrochemical potential, hydrostatic-chemical (mechanochemical) potential (exceptionally in the presence of the pressure difference) and surface-chemical potential, was first introduced under the isothermal and isobaric conditions. This article then enlightened the equilibrium conditions in case where the release of chemical energy is counterbalanced by the supply of electrical energy, by the supply of hydrostatic work (exceptionally in the presence of ${Delta}p$), and finally by the release of surface energy, respectively, at constant temperature T and pressure p in terms of the modified chemical potential ${mu}_k^+$. Finally, this paper focussed on the difference between chemical and electrochemical equilibria based upon the fundamentals of the isothermal and isobaric equilibrium conditions described above.