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The heat of formation of ethylene is 12.5 kcal. Calculate C=C bond energy in ethaylene from the following data. Heat of atomisation of C=170.9 "kcal/mole",Heat of atomisation of H=52.1 "kcal/mole" bond energy of C-H=99.3 "kcal/mole". |
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Answer» Solution :Given that, `2C(s)+2H_(2)(g) to C_(2)H_(4)(g) {H-overset(H)overset(|)(C )=overset(H)overset(|)-H}` , `DeltaH=12.5` kcal For reactants Heat of atomisation of 2 MOLES of C`=2xx170.9` kcal Heat of atomisation of 4 moles of `H=4xx52.1` kcal For PRODUCTS Heat of formation of 4 moles of C-H BONDS `=-4xx99.3`kcal Heat of formation of 1 mole of C=C bond `=1xx x` [where x is the energy of formation of C=C bond in kcal/mole] Adding up, we get the heat of formation of the reaction given above i.e., `2xx170.9+4xx52.1-4xx99.3+x=12.5` or `x=-140.5` kcal/mole Thus, the bond energy of C=C bond `=+140.5` kcal/mole |
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