In chloroethane, the C-atom of C – Cl bond is sp3 hybridised while in C6H5Cl, the carbon atom is in sp2 hybridisation state. The sp2 hybridised C an atom with a greater s-character is more electronegative and can hold the electron pair of the C – Cl bond more tightly than sp3 – hybridised C-atom in chloroethane with less character. Thus the bond cleavage in chlorobenzene is more difficult and is, therefore, less reactive as compared to chloroethane.
