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In the series ethane, ethylene and acetylene, the C-H bond energy is a.)the same in all the 3 compounds b.)greatest in ethane c.)greatest in ethylene d.)greatest in acetylene

In the series ethane, ethylene and acetylene, the C-H bond energy is 
a.)the same in all the 3 compounds
b.)greatest in ethane
c.)greatest in ethylene
d.)greatest in acetylene

Grade:12th pass

1 Answers

Pawan Prajapati
askIITians Faculty 60787 Points
3 years ago
Answer :

The strength of the C-H bond depends upon the hybridisation of the Carbon atom.
In the formation of a sp hybrid orbital [in acetylene, HC≡CH: one 2s orbital and two hybrid orbitals are involved , so the percent s character is 50%
in the formation of a sp2 hybrid orbital[in ethylene CH2=CH2]: one 2s orbital and three hybrid orbitals are involved, so the % s character is 33%
in the formation of a sp3 hybrid orbital[in ethane , C2H6]: one 2s orbital and four hybrid orbitals are involved, so the % s character is 25%
A 2s- orbital keeps the electron density closer to the nucleus compared to the 2p orbital. So as the percentage s character increases, the hybrid orbital holds the electron closer to the nucleus and the bond becomes shorter and stronger.
Thus the C-H bond is strongest in acetylene, thus the C-H bond energy will be greatest in acetylene.
Hence option d is the correct answer.


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