Question

Certain thermal decomposition reactions result in the formation of oxides. Give balanced equations for the thermal decomposition of the following, which result in the formation of metallic oxide.

(a) Limestone

(b) Lead carbonate

(c) Calcium nitrate

(d) Calcium hydroxide

Answer 1

Thermal decomposition reaction

A chemical reaction in which a single reactant breaks down into two or more products is called a decomposition reaction. A decomposition reaction in which a single reactant breaks down into two or more products in the presence of heat is called a thermal decomposition reaction.

(a) Limestone

It breaks down into calcium oxide and carbon dioxide on heating the limestone(calcium carbonate).

$$\begin{gathered} {\mathrm{CaCO}}_3\left(\mathrm{s}\right)\stackrel{∆}{\to }\mathrm{CaO}\left(\mathrm{s}\right)+{\mathrm{CO}}_2\left(\mathrm{g}\right) \\ \mathrm{Calcium}\mathrm{carbonate}\mathrm{Calcium}\mathrm{oxide}\mathrm{Carbon}\mathrm{dioxide} \end{gathered}$$

(b) Lead carbonate

On heating the lead carbonate, it decomposes into lead oxide and carbon dioxide

$$\begin{gathered} {\mathrm{PbCO}}_3\left(\mathrm{s}\right)\stackrel{∆}{\to }\mathrm{PbO}\left(\mathrm{s}\right)+{\mathrm{CO}}_2\left(\mathrm{g}\right) \\ \mathrm{Lead}\mathrm{carbonate}\mathrm{Lead}\mathrm{oxide}\mathrm{Carbon}\mathrm{dioxide} \end{gathered}$$

(c) Calcium nitrate

When calcium nitrate is heated, it converts into calcium oxide, nitrogen dioxide and oxygen.

$$\begin{gathered} 2\mathrm{Ca}{\left({\mathrm{NO}}_3\right)}_2\left(\mathrm{s}\right)\stackrel{∆}{\to }2\mathrm{CaO}\left(\mathrm{s}\right)+4{\mathrm{NO}}_2\left(\mathrm{g}\right)+{\mathrm{O}}_2\left(\mathrm{g}\right) \\ \mathrm{Calcium}\mathrm{nitrate}\mathrm{Calcium}\mathrm{oxide}\mathrm{Nitrogen}\mathrm{dioxide}\mathrm{Oxygen} \end{gathered}$$

(d) Calcium hydroxide

On heating calcium hydroxide, it breaks down to calcium oxide and water.

$$\begin{gathered} \mathrm{Ca}{\left(\mathrm{OH}\right)}_2\left(\mathrm{s}\right)\stackrel{∆}{\to }\mathrm{CaO}\left(\mathrm{s}\right)+{\mathrm{H}}_2\mathrm{O}\left(\mathrm{l}\right) \\ \mathrm{Calcium}\mathrm{hydroxide}\mathrm{Calcium}\mathrm{oxide}\mathrm{Water} \end{gathered}$$