Cold Packs & Endothermic Reactions

You can make your own cold pack by tossing water in the freezer (otherwise known as making ice cubes), but there are chemical reactions you can do to make things cold, too. Reactions that absorb heat from the environment are called endothermic reactions. A common example is a chemical ice pack, which usually contains water and a packet of ammonium chloride. The cold pack is activated by breaking the barrier separating the water and ammonium chloride, allowing them to mix. If you are doing a demonstration, making a cold pack, or just seeking examples of endothermic reactions and processes, there are other chemicals you can react to get a lowered temperature. Show me what to mix...