THERMODYNAMIC SYSTEM
A subject for study in thermodynamics has a generalized name a system. It can be any macroscopic material object, which is distinguished from its environment with the help of either existing in reality, or imaginary boundary surface. A system is a model of a real object for study, reflecting its qualitative and quantitative attributes, which are essential for thermodynamics. If a system cannot exchange energy with its external environment, then it is called isolated, if it cannot exchange matter - then it is closed. In an adiabatically isolated system thermal interchange with the external environment is impossible; in a mechanically isolated work is impossible. A system, which can exchange matter, and, as a consequence, energy, with its environment, is called open system.