Friction, its concomitant thermal processes and wear are analyzed in a tribological system which is formed by a separate fragment of a friction pair element where mechanical energy is dissipated. A phenomenological (macroscopic) interpretation of stationary processes in a thermodynamic perspective is proposed. The tribological system is assumed to form an open thermodynamic system. An original model of a frictional source of heat is formulated. Balancing of mass and energy, especially the first law of thermodynamics, is employed in the discussion. Analytical dependences are found between work of friction, wear, heat of friction, heat carried away to the environment, and physical properties of the system material are determined. Variation of the system temperature and dimensions of the energy dissipation region are taken into consideration. The proposed model is illustrated by means of selected tests. Reference is made to an earlier, energetic interpretation of friction and its associated processes (Maciąg, M., 2010, “Thermodynamic Model of the Metallic Friction Process,” ASME J. Tribol., 132(3), pp. 1–7). A method of defining a tribological system and a new mechanism of frictional heating are some of the original elements. Introduction of these elements to equations of mass and energy balances resulted in new analytical dependences characterizing properties of a tribological system.