In the (Fig. 1.2(a)) we could find an illustration of the thermodynamic system that is defined as a fixed amount of matter or a section in space whose attention is concentratedon the study of thermodynamic properties of the matter or substance. The things outside the system which interacts with the system are called environment or environment. The lining between the system and surroundings is called boundary. Now the boundary might be real or imaginary or can be fixed or moving. As we know that mass and energy transfer can occur through the border.

There are three kinds of the system:

• Closed System
• Open System
• Isolated System

1.3.1 Closed System– it is called a closed system when it has an unchanged mass and energy that can flow in or out the boundary. The Fig. 1.2 (b) describes the closed system where no transfers of massoccur.

1.3.2 Open System– it is called an open system when the boundary crosses along with the heat and work getshifted. Fig. 1.2 (c) represents an open system.

1.3.3 Isolated System– when there is no interaction found observed between the system and surrounding then it is said to be an isolated system. No transfer of mass or energy occurs in this system. So it consists of a fixed mass and fixed power system. Fig. 1.2 (d) shows an isolated system.