Question

Separate out exothermic and endothermic process from the following

${\mathrm{H}}_2\mathrm{O}\left(\mathrm{l}\right)\to {\mathrm{H}}_2\mathrm{O}\left(\mathrm{s}\right)+6\mathrm{kJ}$

Answer 1

Energy changes during a reaction

Reactions in which energy is released are called exothermic reactions, and reactions that involve the absorption of heat are called endothermic reactions. The absorption or evolution of energy occurs due to the energy difference between the reactant and the product.
If the product is of higher energy, the extra energy required by the system for the formation of the product is absorbed from the surroundings, and vice versa.

Freezing of water

In the given reaction, water $\left({\mathrm{H}}_2\mathrm{O}\right)$ in its liquid state gets converted to ice. The reaction involves the evolution of heat. The chemical equation for the reaction is:

$$\begin{gathered} {\mathrm{H}}_2\mathrm{O}\left(\mathrm{l}\right)\to {\mathrm{H}}_2\mathrm{O}\left(\mathrm{s}\right)+6\mathrm{kJ} \\ \left(\mathrm{Water}\right)\left(\mathrm{Ice}\right)\left(\mathrm{Heat}\right) \end{gathered}$$

Since heat is also formed with the products, the energy of the reactant is higher than that of the product. Therefore, it is an exothermic process.