Question

What happens when hydrochloric acid is added to water? Why is the heat given off?

Answer 1

Hint: The formula of hydrochloric acid is HCl and it is a strong acid. Since it is a strong acid, on dilution in water the hydrochloric acid will dissociate into hydrogen ions and chloride ions, and this is an exothermic reaction.

Complete answer:
We know that there are two types of reactions based on the temperature, i.e., exothermic reaction and endothermic reaction. Exothermic reactions are those in which there is a rise in the temperature and the energy is released while endothermic reactions are those in which there is a fall in the temperature and there is the absorption of energy.
The formula of hydrochloric acid is HCl and it is a strong acid. Since it is a strong acid, on dilution in water the hydrochloric acid will dissociate into hydrogen ions and chloride ions. We know that the hydrogen ions are very small and they can readily react with the electronegative atom. Since water contains an oxygen atom which is an electronegative atom and it has the ability to form hydrogen bonding with the hydrogen ions.
So, when the hydrochloric acid is dissolved in water, the hydrogen ions will form hydrogen bonding with the oxygen atom of the water molecule, since this formation is so strong which releases a huge amount of energy and the heat is given off which increases the temperature of the solution.

Note:
The energy released when hydrochloric acid, sulfuric acid, etc are mixed in water is so high that the solution that if the solution comes in contact with the skin, then it can cause burning.