exothermic reaction

[scottstown]

Hello,

There is something that has been puzzling me. Sorry if I don't use the correct terminology, this is not my field.

When a heat pack made of sodium acetate starts its exothermic reaction, does it release heat for only 15 seconds, but feels hot for ~30 minutes because the sodium acetate solution is acting as an insulator?

Or

When a sodium acetate exothermic reaction starts, does the chemical reaction happen for then entire length of the ~30mins.

If the sodium acetate solution is acting like an insulator, could another material be added to maintain the heat for longer?

Also, larger sized heat pads stay hot longer, is that due to size or reaction?

Thank you in advance for any help on the question,
Scott

[Amok]

I don't think that anyone actually knows this for sure. You'd have to know the rate of the reaction. I'm certain that it is a little bit of both.

As to adding an insulator to make the heat last longer, you could do that, but then it wouldn't be so hot, would it?

[Mapes]

I'd imagine the chemical reaction is active during almost the total time, because those thermal packs don't have much thermal mass. You can test this by taking an old pack, heating it up "manually" (e.g., in a plastic bag dipped in hot water, or in an oven), and seeing how long it takes to cool down. This time corresponds approximately to the time the pack would stay hot after the reactants are depleted.

[Amok]

http://www.wonderhowto.com/how-to-make-sodium-acetate-hot-ice-heating-pad-212411/

http://www.youtube.com/watch?v=GAAF5aoKJoM

The reaction seems to occur very fast.