Which of the following is an exothermic reaction?

A

concentrated hydrochloric acid dissolving in water

B

ammonium nitrate dissolving in water

C

ammonium chloride dissolving in water

D

sugar dissolving in water

A. concentrated hydrochloric acid dissolving in water

Explanation:

Chemical reactions may be classified as either exothermic or endothermic. Exothermic reactions are those that release heat energy to the surrounding while endothermic reactions are those that absorb heat from the surrounding. Exothermic reactions includes dissolving an acid in water. For example dissolving Concentrated HCl in water is exothermic as heat is released to the surroundings. The amount of heat released depends on the strength of an acid.