Some features of system approach

1. Thermodynamic system is arbitrary. Choice of system depends upon the type and nature of analysis
2. A system is always demarcated with a boundary
3. It is hypothetical. Valid under the concept that system is continuum.
4. Energy and mass can enter or leave the system boundary
5. Fate of energy (heat and work) inside the system is neither known nor predictable

Classification of system

A system is classified as closed, open or isolated based on the interaction of mass and energy through the system boundary.

In a closed system no mass can transfer across the system boundary but energy can transfer through it.

Fig. 1.3 A Closed System

In an open system both the mass and energy transfer across the system boundary. Boudary for an open system is usually drawn with dotted or broken line

Fig. 1.4 An Open System

In case of an isolated system, no mass or energy can transfer across the boundary.

Fig. 1.5 An Isolated System

In all sort of thermodynamic problems it is essential to recognize the system for formulation. Once the system is identified, next step is to find the energy and mass interaction across the system boundary.