Given, the heat of formation of N2O is ΔHf(exp)=82 kJmol−1.
Again, N2+12O2→N2O
ΔHf(cal)=B.E. of reactants−B.E of products
⇒ΔHf(cal)=[946+12(498)−(418+607)]=170 kJ/mol
Resonance energy is a stabilization energy.
So, resonance energy = ΔHf(exp)−ΔHf(cal)=82−170=−88 kJmol−1