Compute the heat of formation of liquie methyl alcohol is kilojoule per mol using the following data. Heat of vaporisation of liquid methyl alcohol `=38kJ//mol`. Heat of formation of gaseous atoms from the elements in their standard states `:H=218kJ // mol, C=715kJ //mol, O=249kJ //mol.`
Average bond energies`:`
`C-H415kJ//mol, C-O 356kJ//mol, O-H 463kJ //mol.`

Answer

`-275 kJ mol^(-1)`

Explanation

The concened thermochemical reaction is
`C (g) + 4H(g) + O (g) rarr H - underset(H) underset(|)overset(H)overset(|)(C) - O - H, Delta H = ?`
`Delta H_(f) = [Delta H_(C(s) rarr C(g)) + 2 Delta H_(H - H) + (1)/(2) Delta H_(O = O)]`
`-[3 Delta H_(C - H) + Delta H_(C - O) + Delta H_(O - H) + Delta H_("Vap (CH_(3) OH))]`
`= [715 + 2 xx 436 + 249] - 93 xx 415 + 365 + 463 + 38]`
`= - 275 kJ mol^(-1)`