Why are Concentrations Squared in Solubility Equilibrium Constants?

[JFS321]

Hi all,

I'm trying to understand -- really visualize -- the concept of solubility equilibrium constants. But, I can't understand WHY a stoichiometric value, say 2Ag+, is written in an equilibrium constant as [Ag+]^2.

I understand that in a rate law, squaring the concentration makes sense because you may have data indicating that the rate of reaction has increased by a factor of 4.

But, I can't make the mental connection here for solubility equilibrium or any other equilibrium constant. Can anyone help me visualize? Thanks--

 

[gadong]

The justification is quite involved, and proceeds from the concept of the chemical potential. Textbooks on physical chemistry (Levine, Atkins) work through it in full, but you probably won't find it in general chemistry textbooks.

 

[JFS321]

So basically, this is not something that I should intuitively be able to visualize? I think I can put it to rest if that's the case...

 

[Office_Shredder]

If you think it's intuitive that a reaction that includes A+B gives a reaction rate proportional to [A], then when A happens to equal B you should be willing to believe it's still proportional to [A]