The enthalpy of hydrogenation of cyclohexene is `-119.5KJ` . If resonance energy of benzene is `-150.4KJMol^(-1)` , its enthalpy of hydrogenation would be

Options

A. `-269.9KJmol^(-1)`
B. `-358.5KJmol^(-1)`
C. `-508.9KJmol^(-1)`
D. `-208.1KJmol^(-1)`

Explanation

To find the enthalpy of hydrogenation of benzene, we can follow these steps:

### Step 1: Understand the enthalpy of hydrogenation of cyclohexene
The enthalpy of hydrogenation of cyclohexene is given as \(-119.5 \, \text{kJ/mol}\). This value represents the energy change when one mole of cyclohexene reacts with hydrogen to form cyclohexane.

### Step 2: Calculate the enthalpy of hydrogenation of benzene
Benzene requires three moles of hydrogen for complete hydrogenation to form cyclohexane. Therefore, the total enthalpy change for the hydrogenation of benzene can be calculated by multiplying the enthalpy of hydrogenation of cyclohexene by 3:

\[ \Delta H_{\text{hydrogenation of benzene}} = 3 \times (-119.5 \, \text{kJ/mol}) = -358.5 \, \text{kJ/mol} \]

### Step 3: Account for the resonance energy of benzene
The resonance energy of benzene is given as \(-150.4 \, \text{kJ/mol}\). The resonance energy represents the stabilization that benzene experiences due to its delocalized electrons. To find the actual enthalpy of hydrogenation of benzene, we need to subtract the resonance energy from the calculated enthalpy of hydrogenation:

\[ \Delta H_{\text{actual}} = \Delta H_{\text{hydrogenation of benzene}} - \text{Resonance Energy} \]

Substituting the values:

\[ \Delta H_{\text{actual}} = -358.5 \, \text{kJ/mol} - (-150.4 \, \text{kJ/mol}) \]

\[ \Delta H_{\text{actual}} = -358.5 \, \text{kJ/mol} + 150.4 \, \text{kJ/mol} \]

\[ \Delta H_{\text{actual}} = -208.1 \, \text{kJ/mol} \]

### Conclusion
Thus, the enthalpy of hydrogenation of benzene is \(-208.1 \, \text{kJ/mol}\).

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