Thermodynamics

The \(\Delta \mathrm{H}_{(\mathrm{f})}^{\mathrm{o}}\) of \(\mathrm{NO}_2(\mathrm{~g})\) and \(\mathrm{N}_2 \mathrm{O}_4(\mathrm{~g})\) are 16.0 and \(4.0 \mathrm{k} \mathrm{cal} \mathrm{mol}^{-1}\) respectively. The heat of dimerisation of \(\mathrm{NO}_2\) in \(\mathrm{k}\) cal is :