An alternative approach to the theory of the transformation rate in multicomponent systems is proposed. Instead of using the Gibbs energies of phases involved in the transformation and their derivatives, the modified method is based on the chemical potentials. This allows to present the equations governing the first-order phase transitions in a symmetrical 'canonica' form, which is easier to comprehend, use and apply. A connection between the Onsager's irreversible thermodynamics and the energy dissipated at the phase transition is shown. It is demonstrated that at low interface velocities and for some special cases (near the equilibrium, and for diluted solutions), the canonical equations can be solved analytically. It is shown that in some particular cases, the canonical equations reduce to well-known expressions and dependencies widely used in practice. (c) 2004 Elsevier B.V. All rights reserved.