The state of a system may be identified by certain observable quantities such as volume, temperature, pressure and density etc. All the quantities which identify the state of a system are called properties. The thermodynamic properties are divided into the following two classes:
1.Extensive properties. 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. For example, total volume, total mass and total energy of a system are extensive properties.
2. Intensive properties. The properties of the system, whose value for the entire system is not equal to the sum of their values for the individual parts of the system, are called intensive properties. For example, temperature, pressure and density of a system are intensive properties.