estimate Delta H for the following reaction

Question

C2H4 (g)+3O2(g)→2 CO2(g)+2 H2O(g)
So we have (4) C-H bonds and (1) C=C bond or (H = 4*414 + 615= 2271)
For oxygen,
(3) O=O bonds or (H = 3*502=1506)
2CO2 is (2) O=C=O
(H=730*4=2920)
2H2O is (2) H-O-H
or (H=4*464=1856)
Delta H =(2271+1506)-(2920+1586)=-729
But the actual answer is -1614.
Can you please tell me where am I wrong?

Answer 1

You are incorrect in your calculation of the enthalpy of formation of C2H4. The enthalpy of formation of C2H4 is actually +52 kcal/mol. This means that the enthalpy of the reaction is -1614 kcal/mol.