If at 298 K the bond energies of C - H, C - C, C - C and H - H bonds are respectively 414, 347, 615 and 435 kJ mol−1, the value of enthalpy change for the reaction H2C = CH2(g) → H3C − CH3(g) at 298K will be
-125 Kj
CH2 = CH2(g) + H2(g) → H3C − CH3(g)
414 × 4 = 1656 414 × 6 = 2484
615 × 1 = 615 347 × 1 = 347
435 × 1 = 435–––– 347 × 1 = 347––––
2706––––– 2831–––––
ΔH = 2706 − 2831 = − 125 kJ