Halogenation Of Methane

In the same type of reaction, it is possible to understand the difficulty of the reaction by comparing the activation energy of one step to determine the reaction rate.
The reaction between fluorine and methane is a large amount of exothermic, but still requires + 4.2kJ /mol activation energy. Once the reaction occurs, a large amount of heat is difficult to remove, destroying the generated fluoromethanes, and obtaining carbon and hydrogen fluoride, so direct fluorination reaction is difficult to achieve. The reaction of iodine and methane requires an activation energy greater than 141 kJ/mol, and the reaction is difficult to carry out. Chlorination only needs activation energy +16.7 kJ/mol, bromination only needs activation energy +75.3 kJ/mol, so the halogenation reaction is mainly chlorination and bromination. Chlorination is easier to perform than bromination.
Iodine cannot be substituted with methane to form iodomethane, but its reverse reaction is easily carried out.
By adding iodine to the base chain reaction, it can halt the reaction.