Q10.95P - Chemistry: Molecular Nature Of Matter And Change

Question

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

Step-by-Step Solution

Answer

The heat of reaction is -717 kJ

Step 1: Reduction of HCN

Step 2: 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 $=\left(1304-2021\right) \mathrm{kJ}/\mathrm{mol}=-717 \mathrm{kJ}$