Not all reactions give off heat like this. In fact, some actually take in or absorb energy from their surroundings, and the reacting substances feel cold. They’re called endothermic reactions.

Commercial heat packs (containing iron and water, or supersaturated sodium acetate) and cold packs (various ammonium salts) can be used to show exo- and endothermicity. Heat packs that contain iron ...

Incredibly, the reaction between iron and moist air that produces rust is a very exothermic process and generates lots of heat. Unfortunately, this particular reaction takes place so slowly that ...