The standard molar enthalpies of formation of cyclohexane(l ) and benzen(l) at25^(@) are - 156 and + 49 kJ mol^(-1) respectively. The standard enthalpy of hydrogenationof cyclohexene( l) at 25^(@)C is-119 kJ mol^(-1) . Use these data to estimate the magnitudeof the resonanceenergy of benzene.

The standard molar enthalpies of formation of cyclohexane(l ) and benz

1.	The standard molar enthalpies of formation of cyclohexane(l ) and benzen(l) at25^(@) are - 156 and + 49 kJ mol^(-1) respectively. The standard enthalpy of hydrogenationof cyclohexene( l) at 25^(@)C is-119 kJ mol^(-1) . Use these data to estimate the magnitudeof the resonanceenergy of benzene.
Answer» Solution :Standard enthalpyof hydrogenation of cyclohexene`= -119 KJ mol^(-1)`. This is the observedenthalpy of hydrogenation ofone double bond ( PRESENT in cyclohexene) . If benezene is considered as cyclohexatriene, the observed ENTHALPY of the reaction. wouldbe `= 3 xx(-119)=- 357 kJ mol^(-1)` Calculated enthalpy of the above reaction is `Delta_(r)H =DeltaH_(f)^(@)(C_(6)H_(14)) - [ DeltaH_(f)^(@) (C_(6)H_(6))+3DeltaH_(f)^(@)(H_(2))]= - 156 - ( 49+0) = - 2205 kJmol^(-1)` `:. `Resonance energy = Observed`Delta_(r)H^(@) -` Calculated`Delta_(r)H^(@)` `= ( - 357 ) - ( - 205) kJ mol^(-1) = -152 kJ mol^(-1)`