Why is Kc of the self ionization of water the ionic product of water if the concentration of water is not 1
I am aware that the convention is that since water is used as a solvent, its molarity (being 55.5 M) vastly outweighs those of the other molecules present, so the concentration is essentially constant, and therefore due to this effect we substitute it with 1 to simplify the math
But I've seen some resources state that the self ionization of water has the equilibrium constant itself equal to the ionic product of water? Isn't that just wrong? I mean I assume that the value of 55.5 M is either negligible or irrelevant in this context, but is there any reason they present Kc as EQUAL to Kw? Just convenience?