18. The chain propagating step is fastest in the reaction of an alkane with (1) Fluorine free radical (2) Chlorine free radical (3) Iodine free radical (4) Bromine free radical

Question

Please give answer with explaination

Answer 1

18. The chain propagating step is fastest in the reaction of an alkane with (1) Fluorine free radical (2) Chlorine free radical (3) Iodine free radical (4) Bromine free radical

Answer: #1. Although the Fluorine molecule F₂ has a high activation energy, once it is cleaved, the Fluorine radical readily adds to the alkane, leaving another fluorine radical to react (propagation). The addition is exothermic which increases the rate of the reaction and leads to the fastest mechanism.