Why are haloarenes more stable than haloalkanes ?

Explanation

Haloarenes are less reactive than haloalkanes:
(1) Resonance effect : In haloarencs, the electron pairs on the halogen atom are in conjugation with -electrons of the ring and the following resonating structures are possible :

As a result of resonance, there is delocalisation of electron on C-Cl bond with acquires a partial double bond character. This is also evident form the contribution of structure III, IV, and V. As a result, the bond cleavage in haloarenes is difficult than haloalkanes in which carbon is attached to halogen by a pure single bond. Therefore haloarenes are less reactive towards nucleophilic substitution reactions. (2) Difference in hybridisation states of carton atom in C-X bond : In haloalkanes the carbon atom of the C-X bond is `sp^3` hybridised while in haloarenes the carbon atom attached to halogen is `sp^2` hybridised. The `sp^2` hybridised carbon atom with a greater s-character is more electronegative. It can hold together the electron pair of the bond more tightly than the `sp^3` hybridised carbon atom in alkyl halides with less s-character. Therefore, the C-X bond in haloarenes is shorter than in haloalkanes. The shortening the bond length imparts stability to aryl halides and as a result, the bond cleavage become rather difficult. Therefore haloarenes are less reactive than haloalkanes towards nucleophilic substitutions.