Question

Calculate the reasonance energy of $N_{2}O$ from the following data.of $△H_f^o$ $N_{2}O=82kJmo{l}^{-1}$

Bond energy of N $\equiv$ N, N = N, O = O and N = O bonds are 946, 418, 498 & 607 $kJmo{l}^{-1}$ respectively.

• A. 80 kJ
• B. 85 kJ
• C. 88 kJ
• D. 90 KJ

Answer 1

The correct option is C

88 kJ

N $\equiv$ N (g) + $\frac{1}{2}$(O = O) $\to$ N = N = O(g)
$△H_{f\left(N_{2}O\right)}=[△H_{(N\equiv N)}+\frac{1}{2}△H_{(O=O)}]-[△H_{(N=O)}+△H_{(N=N)}]$
$=[946+\frac{1}{2}\times 498]-(607+418)$
= 946 + 249 - 607 - 418
$\therefore △H_{f\left(NO2\right)}=170kJmo{l}^{-1}$
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