What is Quasi-static process?

 

A quasi- static process is defined as the process in which the deviation from thermodynamics equilibrium is infinitesimal and all the states through which the system passes during a quasi-static process may be treated as quilibrium states. thus it may be defined as a succession of equilibrium states. Thus it may be defined as a succession of equilibrium states. For example, consider a system, a gas contained in a cylinder fitted with a movable piston. If the piston is pushed in very rapidly, the gas immediately behind the piston acquires kinetic energy and is set into turbulent motion which is a non-equilibrium state. In such a case the work done on the system is not governed by the equation dW=PdV. If , however, the piston is pushed in at a infinitely slow rate, the system is at all times in a quiescent equilibrium state and then the process can be considered quasi-static. Thus during a quasi-static process, the system is at every moment infinitesimally near a state of thermodynamic equilibrium and all the states through which the system passes can be described by means of thermodynamic variables referred to the system as a whole. The vanishingly slowness of the process is an essential feature of a quasi-static process.

A quasi-static process is an idealized concept and the conditions for it can never be rigorously statisfied in practice. It is quite distinct from a real physical process always involves non-equilibrium intermediate states. A quasi-static process in contrast to a real process , does not involve considerations of rates , velocities or times. A real process is a temporal succession of equilibrium and non-equilibrium states whereas a quasi-static process is an ordered succession of equilibrium states.