Question

Fill in the blanks by selecting correct word/term given in brackets.

Heat is liberated in an ___ reaction. (exothermic/endothermic)

Answer 1

Step 1: Endothermic reaction

A chemical reaction involves the formation or breaking of a bond. Therefore, it always involves an energy change. The energy of the product can be higher or lower than the reactant.

If the energy of the reactant is lower than the product, the reactant will require extra energy for conversion to the product. The reactant absorbs this energy in the form of heat. These reactions are called endothermic reactions. Therefore, heat is used up in an endothermic reaction.

Step 2: Exothermic reaction

If the energy of the products is lower, the excess energy formed during the conversion is liberated in the form of heat. These reactions are called exothermic reactions. Therefore, heat is liberated in an exothermic reaction.

An example of an exothermic reaction is the formation of carbon dioxide $\left({\mathrm{CO}}_2\right)$ from carbon $\left(\mathrm{C}\right)$ and Oxygen $\left({\mathrm{O}}_2\right)$. The chemical equation for the reaction is:

$\mathrm{C}\left(\mathrm{s}\right)+{\mathrm{O}}_2\left(\mathrm{g}\right)\to {\mathrm{CO}}_2\left(\mathrm{g}\right)+\hspace{0.17em}\mathrm{heat}$

Therefore, heat is liberated in an exothermic reaction.