This paper discusses the construction of a dynamic energy balance equation using boundary conditions conventionally defined for a thermodynamic system. With routine modifications, the equation can be applied to a wide variety of engineering systems. The equation is derived for a moving system with a flexible, permeable boundary. It is assumed that the boundary conditions along with the energy and material flows through the boundary are known. The energy and material flows represent heat and work interactions and condctive material exchange between the system and surroundings. Routine vector equations enable us to convert the surface conditions into local and global balance equations. A simple procedure for modifying the energy equation is given. The restrictions imposed on a system are limited to continuity and the local equilibrium hypothesis. Several examples of the application of the derived balance equation are shown. One of these examples involves the contruction of the Gibbs equation. The general applicability of this equation is discussed. Other examples include condtructing the energy balance equations for conventional control mass and control volume systems as well as for heat conduction.