1i think 49 KJ/mol i had not solve if i m not wrong i had solved it before some days but if u have option near49.1 then tat will be more accurate
The standard molar enthalpies of formation of cyclohexane (1) and benzene (1) at 25°C are – 156 and + 49 kJ
mol–1, respectively. The standard enthalpy of hydrogenation of cyclohexene(1) 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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2 Answers
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106Enthalpy of formation of 3 C-C double bonds
= ΔHf(cyclohexane) - ΔHf(benzene)
= -156 - (49) kJ
= -205 kJ
Now it is given that,
Cyclohexene + H2 → cyclohexane ; ΔH = -119kJ
Now, theoretical enthalpy of formation of 3 C-C double bonds in benzene ring
=3*(-119)kJ
=-357kJ
So, resonance energy of benzene is = -357 - (-205)kJ
= -152 kJmol-1
btw this was IIT 1996 question right?