Removing the mystery of entropy and thermodynamics . Part 4

Recall that a reversible process is specified in the Clausius algorithm, dS = d̄Qrev/T . To appreciate this subtlety, it is important to understand the importance of reversible processes in thermodynamics. Although they are idealized processes that can only be approximated in real life, they are extremely useful. A reversible process is typically infinitely slow and sequential, using a large number of small steps that can be reversed in principle. In the limit of an infinite number of steps, all thermodynamic states encountered for all subsystems and surroundings are equilibrium states.