question_answer 1)

  The intermediate carbocation formed in the reactions of \[HI,\text{ }HBr\]and \[HCl\] with propene is the same and the bond energy of \[HCl,HBr\]and \[HI\] is\[430.5\text{ }kJmo{{l}^{-1}}\], \[363.7\text{ }kJmo{{l}^{-1}}\]and\[296.8\text{ }kJmo{{l}^{-1}}\]respectively. What will be the order of reactivity of these halogen acids?

Answer:

  Weaker is the bond, greater is the reactivity of halogenated acid. \[\xrightarrow[\text{Decreasing}\,\text{reacticaity}]{HI>HBr>HCl}\] Since the bond dissociation energy decreases in the order: \[HCl(430.5kJmo{{l}^{-1}})>HBr(363.7kJmo{{l}^{-1}})>HI(296.8kJmo{{l}^{-1}})\]therefore, the reactivity of the halogen acids decreases in the reverse order : \[HI>HBr>HCl\]