Question

why ammonium nitrate on dissolving in water becomes cool

Answer 1

Ammonium nitrate consists of ionic bonds packed tightly together. When it comes into contact with water, the polar water molecules interfere with those ions and eventually make them disperse. It takes energy to do this, which is absorbed from the surroundings and makes the solution cold. While some heat is produced when the ammonium nitrate ions interact with the water molecules (i.e., an exothermic reaction), it is a lot less than what is needed for the water molecules to disperse the strong ionic bonds of the ammonium nitrate, so the overall process is an endothermic reaction, or one that absorbs energy from its surroundings.

Answer 2

This kind of endothermic process is used in instant cold packs. These coldpacks have a strong outer plastic layer that holds a bag of water and a chemical, or mixture of chemicals, that result in an endothermic reaction whendissolved in water. ... Many instantcold packs contain ammonium nitrate.

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