those gelbag handwarmers with a piece of metal inside that you snap, and can reuse after boiling the bag
In: Chemistry
These handwarmers contain a supersaturated solution – basically there’s waaaaay more “chemical” in that liquid than there should be
When you snap the metal, it disturbs the solution – the solution suddenly “realises” that there is too much chemical and is like “I can’t be a liquid, there’s too much of me!” so it starts becoming a solid. That starts at the point where you created the disturbance and spreads out, kinda like each solid part is telling the liquid around it that it too can be solid
This process is “exo-thermic”, meaning it outputs heat as a sort of by-product. You can reverse the process by giving the heat back to the solid, by boiling it in water. Makes it liquid again
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I am not a chemist, and its actually really hard to simplify supersaturated solutions. I hope someone can clarify this a bit more! From what I recall, in certain conditions you can dissolve more of a solid into a liquid than you would otherwise be able to do.
Dissolved the normal maximum – saturated
Dissolved more than the normal maximum – supersaturated
But this is… unstable? So disturbing the liquid causes it to suddenly solidify, resulting in a hardening process. Boiling it raises the temp to a point where it can now dissolve more solid or something, so it becomes a liquid again
Yes, they contain a supersaturated solution of sodium acetate. Supersaturated means that it has more than the maximum possible amount of sodium acetate dissolved in it. This is pretty unstable in a sense because the sodium acetate would rather be a crystal than be dissolved at that point so it will take any opportunity to crystallize. That is what the metal is for, bending it creates an impurity which the crystals can start growing on which will cause all of the sodium acetate to crystalize all at once. This process is what you would call “exothermic”, which means that it produces heat. That is what makes these handwarmers work.
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