Reversible process

A process that can be retraced back to its original position even after the system passes through the same states as in the direct process, and finally the system and the surroundings reaches to its original states without any change in the universe is called reversible process.

This process is ideal process for which the following conditions should be required

1. The changes must take place infinitesimally slow rate.
2. The system must always be thermal equilbrium with the surroundings

Above two conditions tells the process is quasi-static process.

3. There should be no loss of energy due to conduction, conviction or dissipation of energy against any resistance such as friction, viscosity etc.
4. No amount of heat transformed in to magnetic or electric energy
Examples for reversible process are
A quasi-static isothermal expansion of an ideal gas in a cylinder fitted with a frictionless movable piston, Peltier effect and Seebeck effect and Fusion of ice and vaporisation of water.