Thermodynamic System
We give some definitions we need to develop the theory of thermodynamics. The object under stduy is known as system, which represents a finite quantity of matter or a prescribed region of space of finite extent with definite boundaries. The term surroundings designates everything exterior to the system. As surrounding medium is taken a medium of practically unrestricted dimensions whose parameters remain unaltered.
Isolated systems are those which are entirely uninfluenced by changes in their environment. In particular, there is no possibility of the transfer either of enery or of matter across the boundaries of the system.
Closed systems are those in which there is the possibility of energy exchange with the environment, but there is no transfer of matter across the boundaries. This does not exclude the possibility of a change of internal composition due to chemical reaction. The mass of the system remains constant.
Open systems are those which can exchange both energy and matter with their environment. An open system is thus not defined in terms of a given piece of material rather as a region of space with geometrically defined boundaries across which there is the possibility of transfer of energy and matter.
The word body is used to refer either to the isolated or closed system.
For process is intended every transformations taking the system from an equilibrium state to another.