The intermediate carbocation formed in the reaction of HI, HBr and HCl with propene is the same and the bond energy of HCl, HBr and HI is 430.5 kJ mol^(-1), 363.7kJ mol^(-1) and 296.8 kJ mol^(-1) respectively. What will be the order of reactivity of these halogen acids ?

The intermediate carbocation formed in the reaction of HI, HBr and HCl

1.	The intermediate carbocation formed in the reaction of HI, HBr and HCl with propene is the same and the bond energy of HCl, HBr and HI is 430.5 kJ mol^(-1), 363.7kJ mol^(-1) and 296.8 kJ mol^(-1) respectively. What will be the order of reactivity of these halogen acids ?
Answer» Solution :Hydrogen halides (HCl, HBr, HI) ADD upto a alkanes to form alkyl halides. The order of reactivity of the hydrogen halides is `hI gt HBr gt HCl`. Reactivity of HX depends on bond dissociation enthalpy of HX. Bond enthalpy of HI `(296.kJ mol^(-1)) lt HBr (363.7 kJ mol^(-1)) lt HCl (430.5 kJ mol^(-1))` is in this order hence there activity is in reverse order : `HCl lt HBr lt HI` `CH_(3)-CH=CH_(2)+H^(+)` slow step `RARR CH_(3-) ""^(+)CH-CH_(3)+X^(-)` fast `rarr CH_(3)-CHX-CH_(3)` Slow step is RATE determining step and it depends on the availability of `H^(+)`. Availability of `H^(+)` depends on bond dissociation enthalpy of HX.