The following heterogeneous equilibrium occurs in a sealed container at constant temperature:
2NH4Cl(s) ⇌ NH3(g) + HCl(g) + 2NH3(aq)
The initial Kc written by a classmate is
Kc = [NH3(g)][HCl(g)][NH3(aq)] / [NH4Cl]^2
Rewrite the expression correctly and, in one concise sentence, justify the omission of any species you removed.