Calculate the enthalpy of combustion for the following reaction :
`2HC-= CH +5O_(2) rarr 4CO_(2) +2H_(2)O`
The bond energies of `C-H, C-=C, O=O, C=O`, and `O-H` bonds are `414,812, 494,707`, and `436 kJ mol^(-1)`, respectively.

Explanation

Sum of bond energies of reactants
`=4 xx C-H +2 xx C-=C +5 xx (O=O)`
`=4 xx 414 +2 xx 812 +5 xx 494`
`=1656 +1624 +2470 = 5750 kJ`
Sum of bond energies of products
`= (8 xx C =0) +4 xx 0 -H =8 xx 707 +4 xx 463`
`= 5656 +1852 = 7508 kJ`
Enthalpy of combustion,
`DeltaH = 5750 - 7508 =- 1758 kJ`