[Big-Daddy]

This question has been nagging for me a while. I have only ever seen K_sp applied to dissolution of ionic solids. What about organic substances? What is our equilibrium measure for their dissolution?

I mean, if we wanted to write a K_sp equation it could just be of the form, e.g. ethanol (s)  ethanol (aq) i.e. K_sp≥[ethanol (aq)], with equality K_sp=[ethanol (aq)] when the solution is saturated with respect to ethanol.

[Big-Daddy]

Edit: I suppose maybe for ethanol it would be ethanol (l)  ethanol (aq)? Depends on whether K_sp is defined as from standard state to dissolved in solution, or from solid crystal to dissolved in solution (seems hard to tell, because the standard state of everything for which we seem to use K_sp, is a solid crystal).

[Corribus]

Since in this case there is no dissociation that needs to be worried about, it's just simpler to deal with more standard formulations for the thermodynamics (enthalpy, entropy) of mixing. I suppose you could still use a K_sp formalism if you wanted to, but I wouldn't see much point to it.

[Big-Daddy]

Since in this case there is no dissociation that needs to be worried about, it's just simpler to deal with more standard formulations for the thermodynamics (enthalpy, entropy) of mixing. I suppose you could still use a K_sp formalism if you wanted to, but I wouldn't see much point to it.

Ah... but then I'm thinking the maths would be a bit odd when it comes to concentrations/activities? How would we try to define the equilibrium constant for the mixing process at all (there must be an equilibrium constant I assume - otherwise you could get infinite amounts of an organic liquid into water)? Something like K = ethanol (l)  ethanol (aq) now seems a bit odd given that, in mixing, we essentially are "dissolving" some water in ethanol too, no?