The stability of the following alkali metal chlorides follows the order

Stability of a compound depends upon its enthalpy of formation ΔHf . The more negative value of ΔHf shows more stability of a compound. Thus KCl is more stable then LiCl,ΔHf for LiCl =−408  kj/molΔHf for KCl = −436  kj/mol∆Hf for CsCl = -443 kj/mol