The heat of formation of ethane is `-19.46 kcal`. Bond enegries of `H-H, C -H` and `C- C` bonds are `104.18, 99.0` and `80.0 kcal`, respectively. Calculate the heat of atomisation of graphite.

Explanation

Given: `2C(s) +3H_(2)(g) rarr C_(2)H_(6)(g), Delta_(f)H =- 19.46 kcal`
Let the heat of atomisation is `x` kcal
`BE` of reactant `=2 x +3 xx (H-H)`
`= 2x +3 xx104.18 =2x +312.54`
`BE` of products `=(C-C) +6(C-H)`
`= 80 +6 xx 99 = 674`
`DeltaH = 2x +312.54 - 674 =- 19.46`
`:. x = 171 kcal`