Above: Image © Taxiarchos228, Wikimedia Commons

Canadians sure know how to test an athlete — just schedule a Grey Cup game for November!

During these cold weather games, the football players scurry about the field in nylon pants and short sleeves. One might wonder how the quarterbacks manage to complete any of their passes. Obviously adrenalin plays a major role, but there must be something else that contributes to the success of the offensive lines.

Norm Fong, the head equipment manager for the Saskatchewan Roughriders, knows the answer. When Western Canada is in a "deep freeze", Fong outfits all his players with hand warmers on game days. Each one of those waist-belted muffs contains a tiny pocket with an instant-heat hand warmer. Just one packet lasts for the entirety of the three-hour game!

But how do these clever heat packets work?

Two major types of instant warmers currently exist on the market, with heat produced as a bi-product of the activated exothermic reaction (exo = out, therma = heat).

The first type generates heat through the combination of metal (usually iron or platinum) with oxygen in an oxidation reaction. These warmers package a mixture of components into a polypropylene bag: a medium for oxidation (often iron), a catalyst for the reaction (salt), a substance to help disperse the heat (carbon), an insulator (vermiculite), filler (cellulose) and water. When the packet is opened, air rushes in and triggers a very slow combustion reaction, but one that releases heat for at least 7 hours.

Did you know? When rust forms on a drainpipe, this same oxidation reaction occurs.

The following chemical reaction describes the conversion of the iron (Fe) particles in the bag to iron oxide (Fe2O3):

4 Fe(solid) + 3 O2(gas) --> 2 Fe2O3(solid) + heat

A second brand of warmer uses the process of crystallization. To manufacture these heat producers, a solid (usually sodium acetate trihydrate) is first dissolved in boiling water, then allowed to cool very slowly.

The resultant supersaturated solution contains more sodium acetate crystals than can normally dissolve at room temperature. The warmer packets hold this solution and a small metal disc, which when "clicked", creates a nucleation center (the point where crystallization begins). This triggers the sodium acetate trihydrate to crystallize out of solution again.

Did you know? Sodium acetate can be made by mixing vinegar and baking soda (safely in the laboratory with exact proportions)!

As heat was initially consumed in dissolving the solid in water, the reversed process of crystallization releases heat. This chemical reaction only produces warmth for approximately 30 minutes. However, these warmers are reusable: repeated boiling creates a sodium acetate solution again.

These instant heat packs aren't just useful for warming frozen football players' fingers. They are also used by winter sport enthusiasts, hunters, anglers and for soothing aching muscles!

Learn More!

Warmer Hands (And Toes) Through Chemistry. Click Here

Chemical Hand Warmer. Click Here

Hand warmer from Wikipedia, the free encyclopedia

Easy Science Projects from Steve Spangler

Steel Wool generating heat. Click Here

Sodium Acetate from Answers.com

Hand Warmer, Body Warmers, Foot Warmers from Camping Survival

Solidification. Click Here

D.D. Ebbing, General Chemistry (Houghton Mifflin, Boston, ed. 1, 1996) pp.115-116, 492-493.

G. Rayner-Canham, Chemistry (Addison-Wesley, Don Mills, ed. 1, 1988) pp. 236-237.

Karla Badger is currently a PhD student studying cancer biology at the University of Toronto. However, she hails from Manitoba, where snow often falls by Halloween. In her free time, Karla enjoys yoga, rock-climbing, cooking and acting as an editor for a graduate student-run journal, Hypothesis.

CurioCity writer

Article written by a CurioCity expert.

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