Chemical Thermodynamics Part 1

The equation representing various substances involved in chemical reaction isGiven bond enthalpies of various bonds in kJmol‌−1 i.e.
C−C=347,C=C=611,C−H=414,H−H=436
This reaction involves the breaking of 2C−H bonds and formation, of 1C=C bond and 1H−H bond.
∆rH= [Sum of bond enthalpies of reactants] - [Sum of bond enthalpies of products]
=2831−2703
=128kJ/mol