18.2 How do hand warmers work?, and how can I make one?
Description
This article is from the Chemistry FAQ, by Bruce Hamilton B.Hamilton@irl.cri.nz with numerous contributions by others.
18.2 How do hand warmers work?, and how can I make one?
They consist of an aqueous solution of sodium acetate with a small "clicker"
disk to provide a small clean surface that initates crystallisation. The solute
is dissolved into solution by prior warming. When heat is required, the disk
is "clicked" to scrape a small surface, and this clean surface will initiate
the sodium acetate crystallisation from the now supersaturated solution. The
heat of crystallisation is slowly released.
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