Compute the heat of formation of liquid methyl alcohol in kilojoules per mole, using the following data. Heat of vapourisation of liquid methyl alcohol= 38 kJ/mol. Heat of formation of gaseous atoms from the elements in their standard states, H= 218kJ/mol, C= 715 kJ/mol, O= 249 kJ/mol. Average bond energies, C-H = 415 kJ/mol, C-O = 365 kJ/mol, O-H= 463 kJ/mol

Answer

5

Explanation

`C_((s)) rarr C_((g)) , Delta H_(1) = 715`
`(1)/(2) H_(2) rarr H, Delta H_(2) = 218`
`(1)/(2) O_(2) rarr O, Delta H_(3) = 249`
`C_((s)) + 2H_(2) + (1)/(2) O_(2) rarr C_((g)) + 4H_((g)) + O_((g)), Delta H_(4) = 1836`
`C_((g)) + 4H_((g)) + O_((g)) rarr CH_(3)OH_((l)), Delta H = 1836 - [1 xx (C - O) + 3 xx (C - H) + 1 xx (O-H)] - Delta H_("vap")`
`=1836 - (365 + 3 xx 415 + 463 + 38)`
`= 1836 - 2111 = -275` KJ/mole `rArr - 55 xx 5`