# Thermodynamic System

A Thermodynamic System is a Macroscopic Region, defined by boundaries or walls of particular natures, together with the physical surroundings of that region, which determine processes that are allowed to affect the interior of the region, studied using the principles of thermodynamics.

## References

### 2014

• (Wikipedia, 2014) ⇒ http://en.wikipedia.org/wiki/thermodynamic_system Retrieved:2014-6-6.
• A thermodynamic system is a precisely specified macroscopic region of the universe, defined by boundaries or walls of particular natures, together with the physical surroundings of that region, which determine processes that are allowed to affect the interior of the region, studied using the principles of thermodynamics.

All space in the universe outside the thermodynamic system is known as the surroundings, the environment, or a reservoir. A system is separated from its surroundings by a boundary, which may be notional or real but, by convention, delimits a finite volume. Transfers of work, heat, or matter and energy between the system and the surroundings may take place across this boundary. A thermodynamic system is classified by the nature of the transfers that are allowed to occur across its boundary, or parts of its boundary.

A thermodynamic system has a characteristic set of thermodynamic parameters, or state variables. They are experimentally measurable macroscopic properties, such as volume, pressure, temperature, electric field, and others. The set of values of the thermodynamic parameters necessary to uniquely define a state of a system is called the thermodynamic state of a system. The state variables of a system are normally related by one or more functional relationships, the equations of state. In equilibrium thermodynamics, the state variables do not include fluxes, because for a state of thermodynamic equilibrium, all fluxes have zero values, by definition. Equilibrium thermodynamics allows processes which of course involve fluxes, but these must have ceased by the time a thermodynamic process or operation is complete, bringing a system to its eventual thermodynamic state. Non-equilibrium thermodynamics allows its state variables to include non-zero fluxes, that describe transfers of matter or energy or entropy between a system and its surroundings. [1] An isolated system is an idealized system that has no interaction with its surroundings. It is not customary to ask how is its state detected empirically. Ideally it is in its own internal thermodynamic equilibrium when its state does not change with time. A system that is not isolated can be in thermodynamic equilibrium with its surroundings, according to the characters of the separating walls. Or it can be in a state constant or precisely cyclically changing in time - a steady state - that is far from equilibrium. Or it can be in a changing state that is not in thermodynamic equilibrium. Classical thermodynamics considers only states of thermodynamic equilibrium or states constant or precisely cycling in time. An interaction of system and surroundings can be by contact, for example allowing conduction of heat, or by long-range forces, such as an electric field established and maintained by the surroundings. A thermodynamic system is a specialized conception, which does not cover all physical systems. A physical system is a far broader conception, beyond the scope of the present article. The physical existence of thermodynamic systems as strictly defined here may be considered a fundamental postulate of equilibrium thermodynamics, although such is usually not listed as a numbered law of thermodynamics. [2] [3] According to Bailyn, the commonly rehearsed statement of the zeroth law of thermodynamics is a consequence of this fundamental postulate. [4]

Originally, in 1824, Sadi Carnot described a thermodynamic system as the working substance of a heat engine under study.

1. Eu, B.C. (2002). Generalized Thermodynamics. The Thermodynamics of Irreversible Processes and Generalized Hydrodynamics, Kluwer Academic Publishers, Dordrecht, ISBN 1-4020-0788-4.
2. Bailyn, M. (1994). A Survey of Thermodynamics, American Institute of Physics Press, New York, ISBN 0-88318-797-3, p. 20.
3. Tisza, L. (1966). Generalized Thermodynamics, M.I.T Press, Cambridge MA, p. 119.
4. Bailyn, M. (1994). A Survey of Thermodynamics, American Institute of Physics Press, New York, ISBN 0-88318-797-3, p. 22.