Question

Hydrogen cyanide can be catalytically reduced with hydrogen to form methylamine. Use Lewis structures and bond energies to determine Heat of reaction.

Short answer

The heat of reaction is-717 kJ

Step-by-step solution

Reduction of HCN

Heat of reaction

$\begin{array}{c}\mathrm{Energy}\mathrm{required}\mathrm{when}\mathrm{bonds}\mathrm{broken}=1\left(\mathrm{C}-\mathrm{H}\right)+1\left(\mathrm{CN}\right)\mathrm{bonds}\\ =1\left(413\right)+1\left(891\right)\mathrm{kJ}/\mathrm{mol}\\ =1304\mathrm{kJ}/\mathrm{mol}\end{array}$

$\begin{array}{c}\mathrm{Energy}\mathrm{released}\mathrm{when}\mathrm{bonds}\mathrm{formed}=3\left(\mathrm{C}-\mathrm{H}\right)+2\left(\mathrm{N}-\mathrm{H}\right)\mathrm{Bonds}\\ =3\left(413\right)+2\left(391\right)\mathrm{kJ}\\ =2021\mathrm{kJ}\end{array}$

Therefore heat of reaction is$=\left(1304-2021\right)\mathrm{kJ}/\mathrm{mol}=-717\mathrm{kJ}$