The Chemistry of Chemical Hand Warmers

If you live in the parts of the world that are about to get really, really cold this month (if you’re not already there now), you probably recognize the little wonders in the photo above. Hand warmers. Glorious, glorious hand warmers.

Esther Inglis-Arkell over at io9 has an informative little piece up on that site right now about the simple chemistry that causes these little packets to reach 57 ºC without aid of a flame. The secret? Oxidation:

“Small pieces of iron are dispersed in heat packs, isolated by the wrapping on the pack from any oxygen. When the wrapping comes off, the permeable membrane of the pack lets oxygen in and makes it “oxidize” the iron… The iron in the heat packs is surrounded by a chemical that allows the reaction to go much faster. It’s ordinary salt, and it’s why a lot of important iron things get eaten through in the winter, when salt is regularly thrown on streets and sideways to de-ice them, and is then kicked up on to cars and buildings, getting a good rust started on them unless they’re well protected.”

That’s awesome knowledge. For more on how these things works, be sure to check out the full piece linked below.