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The standard molar enthalpies of formati...

The standard molar enthalpies of formation of cyclohexane (l) and benzene (l) at `25^(@)C` are `-156` and `+49 kJ mol^(-1)`, respectively. The standard enthaly of hydrogenation of cyclohenxene (l) at `25^(@)C` is `-119 kJ mol^(-1)` Use this data to estimate the magnitude of the resonance enegry of benzene.

Text Solution

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`C_(6)H_(10)+H_(2) rarr C_(6)H_(12), DeltaH=-119kJ`
`(` involves breaking up of one double bond and addition of one `H_(2)` molecule `)`
`:. C_(6)H_(6)+3H_(2) rarr C_(6)H_(12), DeltaH=-119xx3=-357kJ`
`(` involves breaking up the three double bond and addition of three `H_(2)` molecule `)`
`6C+6H_(2) rarr C_(6)H_(12(l)), DeltaH=-156`
we have , `ul ({:(C_(6)H_(6),+3H_(2),rarr,C_(6)H_(12(l)),,DeltaH=-357),(-,-,,-,+):}) `
`6C+3H_(2) rarr C_(6)H_(6), DeltaH=+201kJ`
Therefore, Resonance energy
`=49-201=-152kJ`
`(Exp.) (` Theoretical `)`
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The standard molar enthalpies of formation of cyclohexane (l) and benzene (l) at 25^(@)C are -156 and +49 kJ mol^(-1) respectively. The standard enthalpy of hydrogenation of cyclohexene (l) at 25^(@)C is -119 kJ mol^(-1) . Use these data to estimate the magnitude of the resonance energy of benzene.

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Knowledge Check

  • The standard molar enthalpies of formation of cyclohexane (l) and benzene (l) at 25^@C are - 156 and +49 KJ mol^(-1) respectively. The standard enthalpy of hydrogenation of cyclo hexene (l) at 25^@C " is" -116 "KJ mol" ^(-1) . Use these data to estimate the magnitude of the resonance energy of benzene.

    A
    `-143"KJ mol"^(-1)`
    B
    `1.52"kJ mol"^(-1)`
    C
    `15.2 "kJ mol"^(-1)`
    D
    None of these

  • The standard enthalpies of formation of CO2(g), H_(2)O(?) and glucose(s) at 25^(@)C are -400kJ/mol, -300kJ/mol and -1300 kJ/mol, respectively. The standard enthalpy of combustion per gram of glucose at 25^(@)C is

    A
    `+2900kJ`
    B
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    C
    `-16.11kJ`
    D
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  • The standard enthalpies of formation of CO_(2)(g),H_(2)O(l) and glucose(s) at 25^(@)C are -400 kJ/mol. -300kJ/mol and -1300 kJ/mol, respectively. The standard enthalpy of cumbusion per gram of glucose at 25^(@)C is

    A
    `+2900kJ`
    B
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    C
    `-16.11kJ`
    D
    `+16.11kJ`

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    The standard molar enthalpies of formation of cyclohexane (l) and benzene (l) at 25^(@)C are -156 and +49 KJ mol^(-1) respectively. The standard enthalpy of hydrogenation of cyclohexene (l) at 25^(@)C is -119 lm mol^(-1) . Use these data to estimate the magnitude of the resonance energy of benzene.

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