The reaction of acid and water is an exothermic reaction since a lot of heat is liberated during the reaction. This heat changes some water to steam explosively which can splash the acid on our face or clothes and cause acid burns.
An exothermic reaction is a reaction in which energy is released in the form of light or heat. Thus, in an exothermic reaction, energy is transferred into the surroundings rather than taking energy from the surroundings as in an endothermic reaction. In an exothermic reaction, the change in enthalpy (ΔH) will be negative.