This paper starts with a short introduction to equilibrium thermodynamics. The whole treatment is restricted to well-known qualitative methods used for mathematical modelling of chemical processes.
The basic results concern the behaviour of phase transition curve near the equilibrium.
Utilizing the fact that the problem of finding the unique vapour-liquid equilibrium curve passing through the critical point can be transformed to a simple solvable nonlinear system of differential equations, the author studies the behaviour of the phase transition curve near the critical point.