From the following bond energies :
| $H - H$ bond energy |
$:\, 431.37 \,kJ\, mol^{-1}$ |
| $C= C$ bond energy |
$:\, 606.10\, kJ \,mol^{-1}$ |
| $C - C$ bond energy |
$:\, 336.49\, kJ\, mol^{-1}$ |
| $C - H$ bond energy |
$:\, 410.50\, kJ\, mol^{-1}$ |
Enthalpy for the reaction,
$\begin{array}{*{20}{c}}
{H\,\,\,\,H} \\
{|\,\,\,\,\,\,\,\,|} \\
{C = C} \\
{|\,\,\,\,\,\,\,\,\,|} \\
{H\,\,\,\,H}
\end{array}\, + \,H - H\, \to \,\begin{array}{*{20}{c}}
{H\,\,\,\,H} \\
{|\,\,\,\,\,\,\,\,|} \\
{H - C - C - H} \\
{|\,\,\,\,\,\,\,\,\,|} \\
{H\,\,\,\,H}
\end{array}\,$
will be .............. $\mathrm{kJ \,mol}^{-1}$