The possibility of synthesis of equilibrium and non-equilibrium thermodynamics (thermostatics and thermokinetics) on classical principles as a deductive and phenomenological theory has been substantiated. This is achieved in the article on the basis of the law of conservation of energy due to its expression through the flows of the energy carrier and the introduction of the missing parameters of the nonequilibrium state of the system. The proposed way of constructing nonequilibrium thermodynamics as a consequence of energodynamics makes it possible to substantiate all the provisions of the theory of irreversible processes (TIP) and classical thermodynamics without involving hypotheses, postulates and considerations of a molecular-kinetic and statistical-mechanical nature. This approach prevents the occurrence of thermodynamic inequalities and opens up the possibility of generalizing TIP to the processes of useful energy conversion, primarily of interest to power engineers, technologists, biophysicists and astrophysicists.