The standard molar enthalpies of formation of cyclohexane...

The standard molar enthalpies of formation of cyclohexane (1) and benzene (1) at $25^{\circ} \mathrm{C}$ are $-156$ and $+49 \mathrm{~kJ} \mathrm{~mol}^{-1}$ respectively. The standard enthalpy of hydrogenation of cyclohexene (1) at $25^{\circ} \mathrm{C}$ is $-119 \mathrm{~kJ} /$ mol. Find resonance energy of benzene. (a) $-152 \mathrm{kJmol}^{-1}$ (b) $-159 \mathrm{~kJ} \mathrm{~mol}^{-1}$ (c) $+152 \mathrm{~kJ} \mathrm{~mol}^{-1}$ (d) $+159 \mathrm{~kJ} \mathrm{~mol}^{-1}$

The standard molar enthalpies of formation of cyclohexane (1) and benzene (1) at $25^{\circ} \mathrm{C}$ are $-156$ and $+49 \mathrm{~kJ} \mathrm{~mol}^{-1}$ respectively. The standard enthalpy of hydrogenation of cyclohexene (1) at $25^{\circ} \mathrm{C}$ is $-119 \mathrm{~kJ} /$ mol. Find resonance energy of benzene.
(a) $-152 \mathrm{kJmol}^{-1}$
(b) $-159 \mathrm{~kJ} \mathrm{~mol}^{-1}$
(c) $+152 \mathrm{~kJ} \mathrm{~mol}^{-1}$
(d) $+159 \mathrm{~kJ} \mathrm{~mol}^{-1}$

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Key Concepts

Aromaticity

Aromaticity is a property of cyclic compounds with conjugated ? electrons that leads to exceptional stability compared to non-aromatic counterparts. This stability, explained by Huckel's rule, is a key factor in understanding the unique reactivity and thermochemical properties of aromatic compounds.

Resonance Energy

Resonance energy is the extra stabilization that a molecule gains due to electron delocalization, particularly in conjugated or aromatic systems. It is measured as the difference between the actual enthalpy of the molecule and the enthalpy of a hypothetical non-resonant structure, highlighting the energetic benefit of resonance.

Standard Molar Enthalpy of Formation

This value represents the heat change when one mole of a compound is formed from its elements in their standard states. It is used to compare the intrinsic stabilities of different compounds and is fundamental in thermochemistry for calculating reaction enthalpies.

Standard Enthalpy of Hydrogenation

This concept refers to the energy change when an unsaturated compound, such as an alkene, reacts with hydrogen to form a saturated compound. The magnitude of the enthalpy change provides insight into the stability of the original compound and the effect of electron delocalization.

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