Question

How are the following indicated in a chemical equation?

Evolution or absorption of heat.

Answer 1

In a chemical reaction, there can be either evolution or absorption of heat.

Based on this, the reactions can be of two types:

1. Endothermic reaction: The reaction in which heat is absorbed.
2. Exothermic reaction: The reaction in which heat is released.

If the heat is absorbed in a reaction, the heat is mentioned on the reactant side. If the heat is released in a reaction, the heat is mentioned on the product side.

The heat can also be written as $∆$(Delta).

For example:

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

Exothermic reaction: $$\begin{gathered} \mathrm{CaO}+{\mathrm{H}}_2\mathrm{O}\left(\mathrm{l}\right)\to \mathrm{Ca}{\left(\mathrm{OH}\right)}_2+∆ \\ (\mathrm{Calcium}\mathrm{oxide})\left(\mathrm{water}\right)(\mathrm{Calcium}\mathrm{hydroxide}) \end{gathered}$$