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 ...

The sodium and acetate ions are ready to bond with each other and with water molecules to form a crystal. When these ions and molecules attract and bond to each other, energy is released. When alcohol ...

A seed crystal can be dropped into a saturated solution of sodium acetate. The solution will suddenly crystallize and turn to solid. Alternately, the solution may be slowly poured out onto a seed ...

The first contains a fine iron powder, salt, and water in a pouch that is permeable to air. When it is exposed to air, the iron begins to rust. This rusting process produces heat. The second contains ...