Question

Calculate the resonance energy of $N_{2}O$ from the following data: ${△}_f{H}^{\circ }$ of $N_{2}O=82kJmo{l}^{-1}$, standard bond enthalpies of $N=N,N=N,O=O$ and $N=O$ bonds are $946,418,498$ and $607kJmo{l}^{-1}$ respectively.

Answer 1

$N\equiv N\left(g\right)+\frac{1}{2}$$O=\overline{O\left(g\right)}\to N=N^{+}=O\left(g\right)$

$\Delta H^{\circ }$ = [Energy required] – [Energy released]

$=(\Delta H_{N\equiv N}+\frac{1}{2}$$\Delta H_{O=O})–(\Delta H_{N=N}+\Delta H_{N=O})$

$=(946+\frac{1}{2}$$\times 498)–(418+607)=170kJ/mol$

So, Resonance energy = Expected value – Observed value of $\Delta H_f^{\circ }=170–82=88kJ/mol$

Ans : $88kJ/mol$