Question

4 (a). Define endothermic reaction with at least one example.

Answer 1

Part 1: Chemical reaction

• A chemical reaction may take place when two or more reactants come in contact with one another resulting in the formation of new substances called products accompanied by the transfer of energy among them.
• The chemical reactions which proceed with the release of heat energy are called exothermic reactions.
• The chemical reactions which proceed with the absorption of heat energy are called endothermic reactions.

Part 2: Endothermic Reaction

Example of endothermic reaction:

• When sodium bicarbonate is heated strongly, it swells up to form sodium carbonate, steam, and carbon dioxide gas. However, the reaction takes place only on heating, i.e., with the absorption of energy.
• $\underset{\mathrm{Sodium}\mathrm{bicarbonate}}{2{\mathrm{NaHCO}}_3\left(\mathrm{s}\right)}\to \underset{\mathrm{Sodium}\mathrm{carbonate}}{{\mathrm{Na}}_2{\mathrm{CO}}_3\left(\mathrm{s}\right)}+\underset{\mathrm{Water}}{{\mathrm{H}}_2\mathrm{O}\left(\mathrm{l}\right)}+\underset{\mathrm{Carbon}\mathrm{dioxide}}{{\mathrm{CO}}_2\left(\mathrm{g}\right)}$