# What is Thermodynamic system ?

The thermodynamic system may be defined as a definite area or a space where some thermodynamic process takes place. It may be noted that a thermodynamic system has its boundaries, and anything outside the boundaries is called its surroundings. The thermodynamic system may be classified into the following three groups.

1. Open System
2. Closed System
3. Isolated System
1. Open System : In this system, the working substance crosses the boundary of the system. The heat and work may also cross the boundary.
2. Closed System : This is a system of fixed mass whose boundaries are determined by the space of the working substance occupied in it. In a closed system, heat and work cross the boundary of the system, but there is no addition or loss of the original mass of the working substance, Thus the mass of the working substance which comprises the system, is fixed.
3. Isolated System : It is a system of fixed mass and no heat or work cross its boundary.

# Properties of a System

The state of a system may be defined 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 types

1. Extensive properties
2. Intensive properties
1. Extensive properties : The properties of the system, whose value of the entire system is equal to the sum of their values of the individual parts of the system, are called extensive properties.
examples of extensive properties : Total volume, Total Mass and Total energy.
2. Intensive properties : The property 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 intensive properties.
examples of intensive properties : Temperature, pressure and Density etc.