Answer:
Benzene does not follow the trend established by the enthalpy values because if the resonance effect.
Explanation:
Considering the trend in the molar enthalpy of combustion of the following chemical compounds that is cyclohexane, cyclohexene, and 1,4‐cyclohexadiene which has the following values for their molar enthalpy of combustion as -3920 kJ/mol, -3800 kJ/mol and -3570.5 kJ/mol respectively.
From the value for molar enthalpy of combustion for the three chemical Compounds above, it can be noted that as we have more bonds the molar enthalpy of combustion values decreases by at least 120 kJ/mol.
Thus, for benzene with 3 bonds we should expect a decrease of 120kJ/mol × 3 bonds = 360kJ/mol. But the value for the molar enthalpy of combustion of benzene is -3560 kJ/mol. That is a decrease of -0010kJ/mol from the value for 1,4‐cyclohexadiene.
This is because of the resonance effect in benzene.
