Thermodynamic system : A thermodynamic system is defined as a quantity of matter or a region in space which is selected for the study. The mass or region outside the system is called surroundings. On the basis of mass and energy transfer the thermodynamic system is divided into three types.

1.Closed system

2.Open system

3.Isolated system

Closed system : A system in which the transfer of energy but not mass can takes place across the boundary is called closed system. The mass inside the closed system remains constant. For example: Boiling of water in a closed vessel.

Open system : A system in which the transfer of both mass and energy takes place is called an open system. This system is also known as control volume. For example: Boiling of water in an open vessel is an example of open system because the water and heat energy both enters and leaves the boundary of the vessel.

Isolated system : A system in which the transfer of mass and energy cannot takes place is called an isolated system. For example: Tea present in a thermos flask. In this the heat and the mass of the tea cannot cross the boundary of the thermos flask. Hence the thermos flak is an isolated system.