EZ Heat Reusable Hand Warmer: Supersaturated Solution Transforms to Solid, Gives Off Heat

The science nerd in me loves my EZ Heat handwarmers.

They’re filled with a supersaturated liquid that gives off heat when provoked/activated to crystallize. Temperature reaches about 130º F, and from my experience the heat lasts for longer than 30 minutes. Boil in water to reset.

Supersaturated solutions were my favorite part of chemistry: A liquid that has more material dissolved into it than it can normally contain, usually with the assistance of heat. Certain circumstances allow this solution to remain liquid indefinitely, until some event creates a crystallizing chain reaction, which turns it to solid. This transformation is exothermic, meaning heat is generated as well.

In the case of the hand warmers, a thin metal tab is inside the plastic packet with the solution. Clicking the tab creates enough of a disruption to begin the reaction. The liquid turns solid in a very awesome looking way. I’m not sure if I like these best for the heat they give off, or to continually watch them activate.

I bought six of these. Here’s the video review I made for Sneakmove.

Here’s how to make a supersaturated solution, from Wikihow.

The two ingredients needed are:
• Some type of crystal source (magnesium sulfate, table salt, sugar, copper sulfate, etc.)
• Water (not sure if other liquids would work, I would imagine they would.)

Take any amount of water, and put it in a glass container (beaker, glass, etc)

Add your crystal source to the water.
Stir and keep adding in more of the crystal source until no more dissolves.
When 5 minutes have gone by without the crystals dissolving any more, you now have a saturated solution.

Now, heat the solution. this can be done in the microwave, on the stove, on a Bunsen Burner, or even on a grill if you want. Just make sure it still stays in the glass container.

When the solution begins to boil, keep adding more of the crystal source, constantly stirring it, until no more crystals dissolve. (<=== make sure you keep the solution on the heat source the entire time you do this step)

Allow the solution to cool. When it has cooled to room temperature, you now have a super saturated solution!