Thermodynamics is a branch of science which deals with the exchange of heat energy between bodies and conversion of the heat energy into mechanical energy and vice versa.
A collection of an extremely large number of atoms or molecules confined within certain boundaries such that it has a certain value of pressure, volume, and temperature is called a thermodynamic system. Anything outside the thermodynamic system to which energy or matter is exchanged is called its surroundings. Thermodynamic system may be of three types:
Open system: It exchanges both energy and matter with the surroundings.
Closed system: It exchanges only energy (not matter) with the surroundings.
Isolated system: It exchanges neither energy nor matter with the surroundings.
When the thermodynamic variables attain a steady value, i.e., they are independent of time, the system is said to be in the state of thermodynamic equilibrium. For a system to be in thermodynamic equilibrium, the following conditions must be fulfilled:
Mechanical equilibrium: There is no unbalanced force between the system and its surroundings.
Thermal equilibrium: There is a uniform temperature in all parts of the system and is same as that of surrounding.
Chemical equilibrium: There is a uniform chemical composition through out the system and the surrounding.