Question

$\Delta H_f^o$ of $N_{2}O$ is $82kJ/mol$ and bond energy for $N_2,N=N,O=O$ and $N=O$ bonds are $946,418,498$ and $607kJ/mol$ respectively. Resonance energy of $N_{2}O$ is:

• A. $-170kJ/mol$
• B. $-252kJ/mol$
• C. $-88kJ/mol$
• D. $-1195kJ/mol$

Answer 1

The correct option is C $-88kJ/mol$

$N_2+\frac{1}{2}{O}_2\to N_{2}O$

$\Delta {}_{f}H=\text{bond energy of reactants}-\text{bond energy of products}$

$\Delta {}_{f}H=[946+\frac{1}{2}\times 498]-[418+607]=170kJ/mol$

$\text{Resonance energy of}{N}_{2}O=\left[\text{actual}\Delta {}_f{H}^0\right]-\left[\text{observed}\Delta {}_{f}H\right]$

$\text{Resonance energy of}{N}_{2}O=82-170=-88kJ/mol$