I’m really confused about this. If we consider $\ce{Ca3(PO4)2}$, it can be seen it undergoes an equilibrium. But why it’s an equilibrium?
This is the equilibrium it undergoes $$\ce{Ca3(PO4)2_{(s)}<=> 3Ca^2+_{(aq)} + 2 PO4_{(aq)}^3-}$$
By the way I’m having a doubt of why some are using backward arrow for a dissociation of a particular precipitate while some are using a solid forward arrow for the same reaction. For an example let’s take $\ce{AgCl(s)}$
Now this is a place where a backward arrow is used, $$\ce{AgCl_{(s)}<=> Ag+_{(aq)} + Cl_{(aq)}-}$$
But I have seen in some books where there is a solid forward arrow instead of back-ward arrow for the dissociation of $\ce{AgCl(s)}$.