Irreversible Process

An irreversible process is a procedure which cannot return both the surroundings and the system to their original conditions. That is, the surroundings and the system would not return to their original conditions when the procedure was reversed. For illustration, an automobile engine does not offer back the fuel it took to drive up a hill as it coasts back downward the hill.

There are many factors which make a procedure irreversible. The most general causes of irreversibility are unrestrained expansion of a fluid, friction, heat transfer via a finite temperature difference, and mixing of two diverse substances. Such factors are present in real, irreversible procedures and prevent these procedures from being reversible.