Why alkenes are more reactive than alkanes?

Explanation

Haloarenes or aryl halide are less reactive than alkyl halide. The low reactivity in comparison to alkyl halide is due to the following reactions :
(i) Resonance effect : In aryl halide the electron pairs .Brtilie halogen atom are in conjugation with n-electrons of the ring and the follo~ing resonating structures are possible:

As a results resonance there is delocalisation of electron on C - Cl bond which acquires a partial double bond character. This is also evident from the contribution. of structure III, IV and V. As a result the bond cleavage in aryl halide is less. reactive towards nucleophilic substitution reaction.
(iz) Hybridisation : In haloalkane the carbon atom of the C - X bond is `sp^3` hybidisation while in haloarene, the carbon atom attached to the halogen `sp^2` hybridisation. The hybridised carbon atom with a greater s-character is more electronegatitive. It can hold the electron pair of the bond more tightly that the `sp^3` hybridised carbon atom in alkyl halide with less s-character. Therefore C - X bond of aryl halide is shorter than alkyl halide.

(iii) Polarity of carbon-halogen bond : The `sp^2` hybridised carbon atom involve in C - X bond in haloarenes molecules is more electronegative than the `sp^3` hybrid carbon atom in alkyl halide. Therefore this `sp^2` hybridised carbon has less tendency to release electron to the Cl-atom and the C-Cl bond in aryl halide is less polar than in alkyl halide. This is supported by the fact that the dipole moment of chlorobenzene is 1. 73 D while the dipole moment of chloro ethene is 2.05 D. Thus lesser the polarity of C - Cl bond, lesser is the reactivity.