[Marco]

I have the following cycle for the combustion of propane:

C3H8(g) + 5O2(g) --------> 3CO2(g) + 4H2O (l)

The following mean bond enthalpies have been given:
E(C-C) = +347; E(C-H)= +413; E(O=O) = +498; E (C=O) = +805; E(O-H) = +464

After calculating the total energy to break the bonds in the reactant molecules and also in the product molecules, I have to calculate an approximate value for the Molar Enthalpy of combustion of Propane. May you help me with this last bit? May you show your calculations and working out?
Many thanks!

[Smrt guy]

Start by putting units on your numbers!  A number without a unit has no meaning.