Calculate the resonance energy of gaseous benzene from the given data
`DeltaH_(C-H)= 416, DeltaH_(C-C)=331 , DeltaH_(C=C)= 591 , DeltaH_("sub")(C, "graphite")=718`
`DeltaH_(diss)(H_(2),g)=436` and `DeltaH_(f)("benzene",g)=83` (all unit in `kJ "mole"^(-1)`)
A. 354
B. 271
C. 437
D. 83

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1 Answers

Correct Answer - B
Required reaction `rArr6C_(("graphite"))+3H_(2(g))rarrC_(6)H_(6(g))`
1. `6C_((g))+6H_((g))rarrC_(6)H_(6(g))`
`Delta H_(1)= -(6xxDelta H_(C-H)+3 Delta H_(C=C)+3 Delta H_(C-C))= -(6xx416+3xx591+3xx331)= -5262 kJ "mole"^(-1)`
2. `6C_(("graphite"))rarr6C_((g)) Delta H_(2)=6xx718=4308`
3. `3H_(2(g))rarr6H_((g))DeltaH_(3)=3xx436=1308`
Adding (1)+(2)+(3)
`6C_(("grapite"))+3H_(2(g))rarrC_(6)H_(6(g))`
`Delta H=Delta H^(@)._(f)(C_(6)H_(6),(g))=Delta H_(1)+Delta H_(2)+Delta H_(3)=354 kJ "mole"^(-1)`
Hence resonance energy `DeltaH_(f)(cal.)-Delta H^(@)._(f)(theo)=354-83= 271 k J "mole"^(-1)`

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