One for the chemists

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Graham_Wright

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www.mastaclimba.com
Santa gave me a hand warmer.

It comprises a plastic bag containing goo and a "thingy" inside which, when clicked, generates heat.

It is rechargeable by heat (can't remember the details).

Any explanations YWKIA.
 
Sodium acetate is used in consumer heating pads or hand warmers and is also used in hot ice. Sodium acetate trihydrate crystals melt at 58 °C, dissolving in their water of crystallization. When they are heated to around 100 °C, and subsequently allowed to cool, the aqueous solution becomes supersaturated. This solution is capable of cooling to room temperature without forming crystals. By clicking on a metal disc in the heating pad, a nucleation centre is formed which causes the solution to crystallize into solid sodium acetate trihydrate again. The bond-forming process of crystallization is exothermic, hence heat is emitted. The latent heat of fusion is about 264–289 kJ/kg. Unlike some other types of heat packs that depend on irreversible chemical reactions, sodium acetate heat packs can be easily recharged by boiling until all crystals are dissolved; they can be reused indefinitely.

OK?
 
Stork_III said:
Sodium acetate is used in consumer heating pads or hand warmers and is also used in hot ice. Sodium acetate trihydrate crystals melt at 58 °C, dissolving in their water of crystallization. When they are heated to around 100 °C, and subsequently allowed to cool, the aqueous solution becomes supersaturated. This solution is capable of cooling to room temperature without forming crystals. By clicking on a metal disc in the heating pad, a nucleation centre is formed which causes the solution to crystallize into solid sodium acetate trihydrate again. The bond-forming process of crystallization is exothermic, hence heat is emitted. The latent heat of fusion is about 264–289 kJ/kg. Unlike some other types of heat packs that depend on irreversible chemical reactions, sodium acetate heat packs can be easily recharged by boiling until all crystals are dissolved; they can be reused indefinitely.

OK?
Click to expand...

Yes - thank you!:)
 
Stork_III said:
Sodium acetate is used in consumer heating pads or hand warmers and is also used in hot ice. Sodium acetate trihydrate crystals melt at 58 °C, dissolving in their water of crystallization. When they are heated to around 100 °C, and subsequently allowed to cool, the aqueous solution becomes supersaturated. This solution is capable of cooling to room temperature without forming crystals. By clicking on a metal disc in the heating pad, a nucleation centre is formed which causes the solution to crystallize into solid sodium acetate trihydrate again. The bond-forming process of crystallization is exothermic, hence heat is emitted. The latent heat of fusion is about 264–289 kJ/kg. Unlike some other types of heat packs that depend on irreversible chemical reactions, sodium acetate heat packs can be easily recharged by boiling until all crystals are dissolved; they can be reused indefinitely.
OK?
Click to expand...

That's all rubbish..... everyone knows they are just magic! Ask any wizard!!
 
We used those held with silver ' speed tape ' onto exposed cine film magazines on Trials Harriers - they actually helped too.

Then one day a berk decided we should leave one unactivated - ie floppy - as a comparison; it fell off in flight.

I have always pictured some farm hand picking up this mysterious silver thing, tweaking it and finding it getting hot...:)
 
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