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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) |
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Answer» Solution :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)` |
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