Question

Explain exothermic reactions with the help of examples.

Answer 1

Exothermic reaction

A chemical reaction in which heat energy is evolved is called an exothermic reaction.

Example: (i) Dissolution of quicklime in water:

When water is added to quicklime, a lot of heat energy is produced along with calcium hydroxide.

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

(ii) Neutralization reaction between acids and bases:

Neutralization reactions between acids and bases are exothermic reactions. When a solution of sodium hydroxide reacts with dilute hydrochloric acid, heat is produced along with sodium chloride and water.

$$\begin{gathered} \mathrm{NaOH}\left(\mathrm{aq}\right)+\mathrm{HCl}\left(\mathrm{aq}\right)\to \mathrm{NaCl}\left(\mathrm{aq}\right)+{\mathrm{H}}_2\mathrm{O}\left(\mathrm{l}\right)+\mathrm{Heat} \\ \mathrm{Sodium}\mathrm{hydroxide}\mathrm{Hydrochloric}\mathrm{acid}\mathrm{Sodium}\mathrm{chloride}\mathrm{Water} \end{gathered}$$