Question

Estimate the fuel value in kJ/g of ethylene gas, H2C=CH2, given the following values in kJ/mol of D(X/Y): O=O, 495; C=O, 799; C=C, 614; O-H, 463; C-C, 348; O-O, 146; C-H, 413; H-H, 436. [Hint: start by writing the balanced equation for complete combustion of ethylene.]

Answer 1

H2C=CH2 +3 O2 ->2 CO2 + 2 H2O
O=O O=C=O O-H-O

Answer 2

Mos is right. Your are breaking one oxygen-oxygen double bond, two carbon hydrogen single bonds and forming two oxygen carbon double bonds and two oxygen hydrogen single bonds. Bond dissociation energy is Bonds broken minus bonds formed.