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

Options

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

Answer

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 kJ/mol. This value represents the energy change when cyclohexene is hydrogenated to cyclohexane.

### Step 2: Calculate the theoretical enthalpy of hydrogenation for benzene
Benzene can be thought of as having three double bonds (due to its structure), so if we were to completely hydrogenate benzene, we would need three moles of H2. Therefore, the calculated enthalpy of hydrogenation for benzene can be estimated as:
\[ \text{Calculated Enthalpy of Hydrogenation of Benzene} = 3 \times (-119.5 \, \text{kJ/mol}) = -358.5 \, \text{kJ/mol} \]

### Step 3: Incorporate the resonance energy of benzene
The resonance energy of benzene is given as -150.4 kJ/mol. The resonance energy indicates the stability of benzene due to its delocalized electrons. To find the actual enthalpy of hydrogenation of benzene, we need to adjust the calculated value by the resonance energy:
\[ \text{Actual Enthalpy of Hydrogenation of Benzene} = \text{Calculated Enthalpy} - \text{Resonance Energy} \]
Substituting the values we have:
\[ \text{Actual Enthalpy of Hydrogenation of Benzene} = -358.5 \, \text{kJ/mol} - (-150.4 \, \text{kJ/mol}) \]
\[ = -358.5 \, \text{kJ/mol} + 150.4 \, \text{kJ/mol} = -208.1 \, \text{kJ/mol} \]

### Step 4: Conclusion
Thus, the enthalpy of hydrogenation of benzene is:
\[ \text{Enthalpy of Hydrogenation of Benzene} = -208.1 \, \text{kJ/mol} \]

### Final Answer
The enthalpy of hydrogenation of benzene is **-208.1 kJ/mol**.

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