Question

Which of the statements is/are true about the reactivity of halogenation of alkanes? The reactivity order is F₂ > Cl₂ > Br₂ > I₂

I. Lower the activation energy for the chain initiation step, more reactive is the halogen

II. Lower the activation energy for the first chain propagation step, more reactive is the halogen

III. More negative is the overall heat of the reaction (∆H_r⁰) of halogenation of alkane, more reactive is the halogen

IV. Lower the activation energy for the second chain propagation step, more reactive is the halogen.

(A) (I), (II) 

(B) (I), (II), (III) 

(C) (II), (III)

(D) (II), (III), (IV)

Answer 1

Correct option (C) (II), (III)

Explanation:

There are two factors that determine the reactivity of the halogenation of alkanes.

1. Lesser the position value of Eact of the first chain propagating step, more reactive is the halogen.

2. Higher the negative values of overall heat of reaction (∆H_r°), more reactive is the halogen. This explains high reactivity and explosive violence with which F₂ reacts with CH₄