Applied aspects of the classical thermodynamics Part III*. <...> Thermodynamics of model gases A. A. Sobko A. M. Prokhorov Academy of Engineering Sciences, 19 Presnensky Val, Moscow, 123557, Russia E-mail: ainrf@mail.ru Obtained is the exact expression of a transition heat for first-order phase transitions. <...> It is shown that the generalized equation for the Van-der-Vaals—Berthelot gas describes a real gas quantitatively and qualitatively. <...> PACS: 64.60.Bd, 64.60.F, 64.70.F, 51.30.+i Keywords: first-order phase transitions, transition heat, melting heat, molecule volumes, surface tension coefficient, Berthelot gas. * Part I of this article (Calculation of a transition heat for first-order phase transitions) has been published in No. 1, 2011. <...> Part II of this article (Certain consequences out of expressions of a transition heat for first-order phase transition) has been published in No. 4, 2011. <...> Получено точное выражение для теплоты перехода фазовых превращений первого рода, а также получены выражения, связывающие теплоту испарения и теплоту плавления с другими термодинамическими параметрами процессов. <...>