Q53. The enthalpy of formation of ethane $\left( \mathrm { C } _ { 2 } \mathrm { H } _ { 6 } \right)$ from ethylene by addition of hydrogen where the bond-energies of $\mathrm { C } - \mathrm { H } , \mathrm { C } - \mathrm { C } , \mathrm { C } = \mathrm { C } , \mathrm { H } - \mathrm { H }$ are $414 \mathrm {~kJ} , 347 \mathrm {~kJ} , 615 \mathrm {~kJ}$ and 435 kJ respectively is $\quad \mathrm { kJ }$