The halogens`(X_(2))` have strong electron accepeting tendency.They are therefoe, powerful oxidising agents .The relative order of oxidising powers of halogens is:
`X_(2) : F_(2) gtCI_(2)gt Br_(2) gt I_(2)`
`E^(@)`: 2.84Vgt1.36V 1.09 V 0.54 V
Fluorine is the strongest oxidising agnet (oxidant ) .It cn be justifie by the fact theat it can liberate theother halogens from their respective compounds For example,
`2KCI+F_(2)rarr2KF+CI_(2)`
`23KBr+F_(2)rarr2F+Br_(2)`
`2KI+F_(2)rarr2KF+I_(2)`
Among halogen acids (HX) the HI is the strongest reducing agnet or reducatant becauseits bond disociant is the mimimum `(299 Kj mol^(-1))`
Halogen acid : `HF" " HCI" "HBr" "HI`
Bond dissociation enthalply : 566 , 431 ,366, 299
`(kj mol^(-1))` The iodination of methane for examples is of reversible nature becuse HI formed ibn the reaction being a very strong reducing agent converts iodomethane back to methane.
`CH_(4)+I_(2)rarrCH_(3)I+HI`
`CH_(3)I+HIrarrCH_(4)+I_(2)//(CH_(4)+I_(2)ltimpliesCH_(3)I+HI`
Howeever, the halogenation with other halogen acids is not of reversible nature. This justifies that HI is the strongest reducing agent in the hjal,ogen acids.
