In all thermodynamic problems energy transfer to or form the system is observed. To receive, store and deliver energy a working substance is present within the system. The characteristics which can be used to describe the condition of the system are known as properties.

The thermodynamic properties of a system may be divided into the following two general classes:
• Extensive properties
• Intensive properties
Extensive Properties:
A quantity of matter in a given system is divided, notionally into a number of parts. The properties of the system, whose value for the entire system is equal to the sum of their values for the individual parts of the system are called extensive properties. E.g. total volume, total mass and total energy of a system are its extensive properties.

Intensive Properties:
It may be noticed that the temperature of the system is not equal to the sum of the temperature of its individual parts. It is also true for pressure and density of the system. Thus properties like temperature, pressure and density are called intensive properties.