Question

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

Answer 1

As a result of hydrogen bond formation during ionisation.......

Explanation:

Dilution of concentrated hydrochloric acid involves ionisation of the HCl. When this occurs, hydrogen ions undergo reaction with water to form a complex with general formula `H_3O•(H_2O)^+n`, the value of n is variable.

The charge on the ions is concentrated into a very small area because hydrogen is so small. This gives powerful attraction to water molecules with many hydrogen bonds being created. As creating bonds releases energy, the process overall is exothermic.