From the following bond energies: H — H bond energy : 431.37 kJ mol–1 C == C bond energy : 606.10 kJ mol–1 C — C bond energy : 336.49 kJ mol–1 C — H bond energy : 410.50 kJ mol–1 Enthalpy for the reaction, will be (2009)

For the given reaction, enthalpy of reaction can be calculated as = B.E.(reactants) – B.E.(products) = [B.E.(C=C) + B.E.(H–H) + 4 × B.E.(C–H)] – [B.E.(C–C) + 6 × B.E.(C–H)] = [606.10 + 431.37 + 4 × 410.50] – [336.49 + 6 × 410.50] = 2679.47 – 2799.49 = –120.02 kJ mol–1