Calculate the standard enthalpy of formation of `CH_3OH_((l))` from the following data :
(i)`CH_3OH_((l)) +3//2 O_(2(g)) to CO_(2(g)) + 2H_2O_((l)) , Delta_r H^(Ө)=-726 "kJ mol"^(-1)`
(ii)`C_((s)) + O_(2(g)) to CO_(2(g)) , Delta_c H^(Ө)=-393 "kJ mol"^(-1)`
(iii) `H_(2(g)) +1//2O_(2(g)) to H_2O_((l)) , Delta_f H^(Ө)=-286 "kJ mol"^(-1)`

Explanation

The equation we aim at : `C_((s)) +2H_(2(g)) + 1//2 O_(2(g)) to CH_3OH_((l)) , Delta_fH^(Ө)=pm` …(iv)
Multiply equation (iii) by 2 and add to equation (ii)
`C_((s)) +2H_(2(g)) to CO_(2(g)) +2H_2O_((l)) " " DeltaH`=-(393+522) =-965 kJ `"mol"^(-1)`
Subtract equation (iv) from equation (i)
`CH_3OH_((l)) +3//2 O_(2(g)) to CO_(2(g)) + 2H_2O_((l)) , DeltaH=-726 "kJ mol"^(-1)`
Subtract : `C_((s)) + 2H_(2(g)) + 1//2 O_(2(g)) to CH_3OH_((l)) , Delta_fH^(Ө)=-239 "kJ mol"^(-1)`