Reversible Process - example


1 – removing sand by shovel;   2 – adding sand by shovel

In the limit that we remove one sand particle at a time, path 1 and path 2 will be indistinguishable. In this case, the excess work is (almost exactly) zero and the process corresponding to path AE is reversible.

Maximum amount of work a system can perform in going from one state to another is achieved when the system moves along a reversible path.





For the reversible expansion, the work we need to do on the system to compress it has the same magnitude as the work we received during the expansion process. Indeed, we could raise a weight during the expansion and then allow it to be lowered during the compression process. Similarly the heat put into the system by us (the surroundings) during the expansion process has the same magnitude as the heat received by us during the compression process. The result is that when the system has been restored back to its initial state, so have the surroundings. There is no trace of the overall process on either the system or the surroundings. That is another meaning of the word ``reversible.''