Is a reversible expansion or compression process necessarily

Is a reversible expansion or compression process necessarily quasi-equilibrium? (b) Is a quasi-equilibrium expansion or compression process necessarily reversible? (c) If an adiabatic System (gaseous or liquid) bus work input only due to a paddle-wheel, performed in a quasi-equilibrium manner, is the process a reversible one? Explain why or why not.

Solution

(a) A \'reversible\' process means the path taken to reach from state A to B can be retraced exactly the same way. This is possible only when both the forward and the reverse path the system always remains in thermodynamic equilibrium. Hence, the process has to be \"infinitesimally\" slow/small. Hence, a quasi-static process is a necessary condition for a reversible process.

(b) By the basic definition, a quasi-equilibrium process is reversible.

(c) No. The paddle wheel work is by frictional activity (even if it is done in a quasi-equilibrium manner). The gas or liquid system cannot transfer the same amount of work back to the paddle system.