[jlhannah]

Use average bond energies from the datasheet to estimate the enthalpy change (heat change, ΔH) in
kJ/mol for the following reaction. Note that the carbon atoms are bonded to one another in both C2H4 and
C2H6.
 H2(g) + C2H4(g) ----> C2H6(g)

According to the answer key, it should be approx. -130 kJ/mol, but I don't even know where to start with this! 
I also attached our data sheet.

[Borek]

Enthalpy of the compound is approximately equal to sum of enthalpies of its individual bonds.