1. The problem statement, all variables and given/known data Calculate an approximate heat of combustion for propane (C3H8) in kilojoules per mole by using the bond dissociation energies in the table. (The strength of the O=O bond is 498 kJ/mol, and that of a C=O bond in CO2 is 804 kJ/mol.) 2. Relevant equations C3H8 + 5O2 → 3CO2 + 4H2O ΔHrxn = ΣD(reactants) - ΣD(products) http://imgur.com/a/G6e1A 3. The attempt at a solution Looked at propane model found 8 C-H bonds and 2 C-C bonds. 5 O-O (double bonds) found in oxygen 2 C-O bonds found in carbon dioxide 2 H-O bonds found in water (8(410)+2(350)+5(490)) - (2(804)+4(2*460))= 1182 kJ/mol (obviously not right. Combustion is exothermic) Could anyone help?