The enthalpy of formation of ethane (\( \mathrm{C_2H_6} \)) from ethylene by addition of hydrogen where the bond-energies of \( \mathrm{C{-}H} \), \( \mathrm{C{-}C} \), \( \mathrm{C{=}C} \), \( \mathrm{H{-}H} \) are \( 414 \, \text{kJ} \), \( 347 \, \text{kJ} \), \( 615 \, \text{kJ} \) and \( 435 \, \text{kJ} \) respectively is - ______ \( \text{kJ} \).