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Calculate the heat of formation of benzene from the following data, assuming no resonance. Bond energies : C-C=83 kcal C=C=140 kcal C-H=99 kcal Heat of atomisation of C=170.9 kcal Heat of atomisation of H=52.1 Kcal |
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Answer» Solution :We have to calculate `DeltaH` for the reaction `6C(s)+3H_(2)(g) to C_(6)H_(6)(g)`  For REACTANTS HEAT of atomisation of 6 moles of `C=6xx170.9` KCAL Heat of atomisation of 6 moles of `H=6xx52.1` kcal For products Heat of formation of 6 moles of `C-H` bonds `=-6xx99` Heat of formation of 3 moles of C-C bonds `=-3xx83` Heat of formation of 3 moles of C=C bonds `=-3xx140` On adding, we get heat of formation of `C_(6)H_(6)`, i.e., `DeltaH=6xx170.9+6xx52.1-6xx99-3xx83-3xx140=75.0`kcal |
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