Calculate the reasonance energy of N2O from the following data.of △HofN2O=82kJmol−1
Bond energy of N ≡ N, N = N, O = O and N = O bonds are 946, 418, 498 & 607 kJmol−1 respectively.
A
80 kJ
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B
85 kJ
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C
88 kJ
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D
90 KJ
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Solution
The correct option is C
88 kJ
N ≡ N (g) + 12(O = O) → N = N = O(g) △Hf(N2O)=[△H(N≡N)+12△H(O=O)]−[△H(N=O)+△H(N=N)] =[946+12×498]−(607+418)
= 946 + 249 - 607 - 418 ∴△Hf(NO2)=170kJmol−1
The resonance energy of a compound is a measure of the extra stability of the conjugated system compared to the corresponding number of isolated double bonds.
Therefore the resonance energy = difference between observed heat of formation - calculated heat of formation
= 82 - 170
= 88 KJ mol