Question

Name a substance which on heating decomposes but does not leave any residue.

Answer 1

1. Definition: Decomposition reaction is defined as a reaction where a single reactant breaks down to give two or more products under the influence of physical or chemical conditions.
2. Ammonium nitrate ( ${\mathbf{NH}}_{\mathbf{4}}{\mathbf{NO}}_{\mathbf{3}}$) on decomposition gives Nitrous oxide (${\mathbf{N}}_{\mathbf{2}}\mathbf{O}$) and Water vapour (${\mathbf{H}}_{\mathbf{2}}\mathbf{O}$).
3. The reaction is shown below.
   $$\begin{gathered} {\mathrm{NH}}_4{\mathrm{NO}}_3\left(\mathrm{s}\right)\stackrel{∆}{\to }{\mathrm{N}}_2\mathrm{O}\left(\mathrm{g}\right)+2{\mathrm{H}}_2\mathrm{O}\left(\mathrm{g}\right) \\ \mathrm{Ammonium}\mathrm{Nitrous} \\ \mathrm{nitrate}\mathrm{oxide} \end{gathered}$$
4. As Nitrous oxide (${\mathbf{N}}_{\mathbf{2}}\mathbf{O}$) and Water vapour (${\mathbf{H}}_{\mathbf{2}}\mathbf{O}$) are in the gaseous state, no residue is left behind.
5. Therefore, a substance that on heating decomposes but does not leave any residue is Ammonium nitrate (${\mathbf{NH}}_{\mathbf{4}}{\mathbf{NO}}_{\mathbf{3}}$).