One of the activity of laboratory is the addition of acid to water.
The addition of acid to water make it easier for the reaction so that the acid gets diluted safely. On the other hand if water is added to acid it will get splash vigrously and may injure the hand of the chemist. The addition of water directly to acid contribute to exothermic reaction and releases more heat which may result in spraying around.
Adding acid to water, result in solution with very dilute solution and releases small heat. This small heat is not sufficient even to vaporizes a single drop of water.
