What is quasi-equilibrium?

Answer 1

In equilibrium, after any displacement from equilibrium, the system will always seek to return to the same state. In quasi-equilibrium, a disturbance of the system may result in the system shifting to a new, more stable equilibrium state. An example of quasi equilibrium is a supersaturated liquid with no nucleation sites for the growth of crystals. It may remain in the same quasi-equilibrium state indefinitely as long as no nucleation sites are introduced. As soon as some seed crystals are introduced however, the solute in the supersaturated solution will begin to crystalize out of the soultion until enough is removed to reduce the solution to true equilibrium. At that point, no mater what additional crystals are added or removed from the solution, the concentration of the solute will remain the same.