How come Ksp expressions don’t have the reactant on the bottom?

Question

I'm a little confused about this one...

Answer 1

Because if AgCl <===> Ag+ + Cl-, and you have a little bit of undissolved AgCl on the bottom, that is the same as if you had a whole pile of AgCl undissolved on the bottom. So [AgCl] is unchangeable and doesn't come into the calculation. So by convention, [AgCl] undissolved is taken as "1.000," and Ksp = [Ag+][Cl-].

Answer 2

they should, UNLESS the reactants are solid and it remains constant, there fore not affecting the ksp