Answer
+42kJ/mol Or +10kcal/mol
Work Step by Step
In the given reaction, bond breaking and bond formation takes place. Bond breaking is endothermic (positive) whereas bond formation is exothermic.
In order to find $\Delta$ $H^{\circ}$ of the reaction, we add the bond dissociation energies, keeping in mind that where the bond formation takes place, the bond dissociation energy is negative.
Therefore,
In kJ/mol
Bonds broken=
$CH3CH2-H=+410$
$I-I= +151$
Bonds formed=
$CH3CH2-I=-222$
$H-I=-297$
$\Delta$$H^{\circ}$= $(+410+151) + (-222) + (-297)$
$\Delta$$H^{\circ}$= $+561+(-519)$
$\Delta$$H^{\circ}$= $+561 -519$
$+42 kJ/mol$
In kcal/mol
Bonds broken=
$CH3CH2-H= -98$
$I-I= -36$
Bonds formed=
$CH3CH2-I=-53$
$H-I=-71$
$\Delta$$H^{\circ}$=$ (+98+36 )+ (-53)+(-71)$
$\Delta$$H^{\circ}$ =$134 + ( -124)$
$\Delta$$H^{\circ}$ = $134 - 124$
$\Delta$$H^{\circ}$= $+10 kcal/mol$