The present paper describes a new way of presentation of the classical theory of capillarity. An approach based on the Ω-potential thermodynamic formalism is used. An explicit definition of the Gibbs excess quantities of the extensive thermodynamic functions is proposed. It is emphasized that the Ω-potential is the only extensive thermodynamic function which, when defined as an excess quantity, is not in fact such a quantity. It holds for the case of two-phase plane-interface equilibrium systems. The work of transformation of a homogeneous system into a heterogeneous one at given conditions, (ΔΩ)T,V,μ, is defined by means of Eq.(39). Different capillary systems and different thermodynamic models for their description can be unified on the basis of Eq.(39).