Answer
Verified
435.6k+ views
Hint: Resonance energy of a molecule is the theoretical difference between the energies of resonance hybrid and the most stable structure of the molecule. It is a measure of extra stability gained by a molecule as a result of resonance.
Complete step by step answer:
Hydrogenation is a chemical reaction between a molecule and hydrogen. Usually an unsaturated compound reacts with molecular hydrogen in order to saturate the compound. The enthalpy change during this reaction is called enthalpy of hydrogenation.
It is given in the question that the enthalpy of hydrogenation of cyclohexene is $ - 119.5kJ/mol$ . The corresponding reaction is shown below.
Cyclohexene contains one double bond. Hydrogenation reaction of cyclohexene involves breaking this double bond and adding two hydrogen atoms and thereby saturating the compound. $ - 119.5kJ/mol$ is the energy involved in the breaking of one double bond.
Benzene also contains a cyclohexane ring. But it contains three double bonds. We have seen that energy involved in breaking one double bond and adding two hydrogens is $ - 119.5kJ/mol$ . So, in order to break three double bonds and add six hydrogens, the energy involved will be three times the value of enthalpy of hydrogenation of cyclohexene.
Hence the expected value of enthalpy of hydrogenation of benzene $ = 3 \times \left( { - 119.5} \right) = - 358.5kJ/mol$
But it is given that enthalpy of hydrogenation of benzene is $ - 208.1kJ/mol$ . Hence the resonance energy of benzene will be different between the calculated value and observed value.
Resonance energy of benzene $ = \left( { - 358.5} \right) - \left( { - 208.1} \right) = - 150.4kJ/mol$
Hence resonance energy of benzene is $ - 150.4kJ/mol$ .
Therefore, the correct option is A.
Note:
Observed value of enthalpy of hydrogenation does not match with the calculated value. This is because of the extra stability of benzene gained by resonance. If benzene is just three alkenes formed in a ring, the observed and calculated values may match. But there are different resonance structures possible for benzene which makes it more stable.
Complete step by step answer:
Hydrogenation is a chemical reaction between a molecule and hydrogen. Usually an unsaturated compound reacts with molecular hydrogen in order to saturate the compound. The enthalpy change during this reaction is called enthalpy of hydrogenation.
It is given in the question that the enthalpy of hydrogenation of cyclohexene is $ - 119.5kJ/mol$ . The corresponding reaction is shown below.
Cyclohexene contains one double bond. Hydrogenation reaction of cyclohexene involves breaking this double bond and adding two hydrogen atoms and thereby saturating the compound. $ - 119.5kJ/mol$ is the energy involved in the breaking of one double bond.
Benzene also contains a cyclohexane ring. But it contains three double bonds. We have seen that energy involved in breaking one double bond and adding two hydrogens is $ - 119.5kJ/mol$ . So, in order to break three double bonds and add six hydrogens, the energy involved will be three times the value of enthalpy of hydrogenation of cyclohexene.
Hence the expected value of enthalpy of hydrogenation of benzene $ = 3 \times \left( { - 119.5} \right) = - 358.5kJ/mol$
But it is given that enthalpy of hydrogenation of benzene is $ - 208.1kJ/mol$ . Hence the resonance energy of benzene will be different between the calculated value and observed value.
Resonance energy of benzene $ = \left( { - 358.5} \right) - \left( { - 208.1} \right) = - 150.4kJ/mol$
Hence resonance energy of benzene is $ - 150.4kJ/mol$ .
Therefore, the correct option is A.
Note:
Observed value of enthalpy of hydrogenation does not match with the calculated value. This is because of the extra stability of benzene gained by resonance. If benzene is just three alkenes formed in a ring, the observed and calculated values may match. But there are different resonance structures possible for benzene which makes it more stable.
Recently Updated Pages
10 Examples of Evaporation in Daily Life with Explanations
10 Examples of Diffusion in Everyday Life
1 g of dry green algae absorb 47 times 10 3 moles of class 11 chemistry CBSE
What happens when dilute hydrochloric acid is added class 10 chemistry JEE_Main
What is the meaning of celestial class 10 social science CBSE
What causes groundwater depletion How can it be re class 10 chemistry CBSE
Trending doubts
Fill the blanks with the suitable prepositions 1 The class 9 english CBSE
Which are the Top 10 Largest Countries of the World?
How do you graph the function fx 4x class 9 maths CBSE
Who was the leader of the Bolshevik Party A Leon Trotsky class 9 social science CBSE
The Equation xxx + 2 is Satisfied when x is Equal to Class 10 Maths
Differentiate between homogeneous and heterogeneous class 12 chemistry CBSE
Difference between Prokaryotic cell and Eukaryotic class 11 biology CBSE
Which is the largest saltwater lake in India A Chilika class 8 social science CBSE
Ghatikas during the period of Satavahanas were aHospitals class 6 social science CBSE