The enthalpy of hydrogenation of cyclohexene is - 119.5 kilojoule per mole. if resonance energy of benzene is -150.4 kilo joule per mole then its enthalpy of hydrogenation would be....

To determine the enthalpy of hydrogenation of benzene, we can use the concept of resonance energy and the enthalpy of hydrogenation of cyclohexene. Let's break this down step by step.

Understanding Hydrogenation

Hydrogenation is a chemical reaction where hydrogen is added to an unsaturated compound, such as an alkene or an aromatic compound. The enthalpy change associated with this reaction indicates how much energy is released or absorbed during the process.

Given Values

• Enthalpy of hydrogenation of cyclohexene: ΔH_{hydrogenation} = -119.5 kJ/mol
• Resonance energy of benzene: RE = -150.4 kJ/mol

Calculating the Enthalpy of Hydrogenation for Benzene

Benzene can be thought of as a fully conjugated system with resonance stabilization. When we hydrogenate benzene, we convert it into cyclohexane, which is a saturated compound without resonance. The difference in stability due to resonance can be factored into our calculations.

Using the Resonance Energy

The enthalpy of hydrogenation of benzene can be calculated using the enthalpy of hydrogenation of cyclohexene and the resonance energy of benzene. The relationship can be expressed as follows:

ΔH_{hydrogenation, benzene} = ΔH_{hydrogenation, cyclohexene} + RE

Plugging in the Values

Now, substituting the known values into the equation:

ΔH_{hydrogenation, benzene} = (-119.5 kJ/mol) + (-150.4 kJ/mol)

ΔH_{hydrogenation, benzene} = -119.5 kJ/mol - 150.4 kJ/mol

ΔH_{hydrogenation, benzene} = -269.9 kJ/mol

Final Result

Thus, the enthalpy of hydrogenation of benzene is approximately -269.9 kJ/mol. This value indicates that the hydrogenation of benzene is a highly exothermic reaction, reflecting the significant energy released when breaking the resonance stabilization of benzene and forming cyclohexane.

Summary

In summary, by considering the enthalpy of hydrogenation of cyclohexene and the resonance energy of benzene, we can effectively calculate the enthalpy of hydrogenation for benzene. This approach highlights the importance of resonance in stabilizing aromatic compounds and how it influences their reactivity.