Answer to Question #62827 in Physical Chemistry for Anahita

Question

What are the mechanisms of preventing a supersaturated solution from being precipitation ?(I know that one of the reasons is that the crystalline nucleous is created in solution but it dissloves again and make the solution supersaturated again specially if the particle is small )

Answer 1

Well, thermodynamically supersaturated solution is a non-stable state, and the reasons of why it doesn't precipitate are quite kinetic.
The kinetic barrier is associated with the fact, that creating of crystalline nuclei doesn't lower the energy of the system, but even increase it due to formation of highly dispersed phase. This barrier is very low and can be overcome with the increasing the fluctuation. It happens then the flask with the supersaturated solution is shaked or treated with sound.
The barrier can also be overcome due to adding the porous heterogeneous phase, because of the energy of the formation of crystals on the surface is itself lower than the energy of formation of dispersed phase in solution.