  The alternative approach to the displacement of gas/liquid equilibrium is
developed on the basis of the Clapeyron equation. The phase transition in the
system with well-established properties is taken as a reference process to
search for the parameters of phase transition in the perturbed equilibrium
system. The main equation, derived in the framework of both classical
thermodynamics and statistical mechanics, establishes a correlation between
variations of enthalpies of evaporation, \Delta (\Delta H), which is induced by
perturbations, and the equilibrium vapor pressures. The dissolution of a
solute, changing the surface shape, and the effect of the external field of
adsorbents are considered as the perturbing actions on the liquid phase. The
model provides the unified method for studying (1) solutions, (2) membrane
separations (3) surface phenomena, and (4) effect of the adsorption field; it
leads to the useful relations between \Delta (\Delta H), on the one hand, and
the osmotic pressures, the Donnan potential, the surface curvature, and the
pore structure, on the other hand. The value of \Delta(\Delta H) has a clear
physical meaning and gives a new insight into our understanding of the
apparently different phenomena. The model is applicable if the change between
entropies of the comparable gas phases is far more than the difference between
entropies of the liquid phases.
