How Hand Warmers Work (THERMAL IMAGING) – Periodic Table of Videos

published on July 18, 2020

We're talking about these funny hand warmers in the shape of a heart and each one contains a liquid and a little metal clicker and the point is that this can generate quite high temperatures which will keep your hand warm inside is sodium acetate that is dissolved in

Water it's a very concentrated solution sodium acetate is made up of ions positively charged sodium negatively charged acetate positive and negative attract each other and so you need energy to pull them apart and you have

To imagine a huge array of these millions and billions of these going alternately positive negative and so on but I can't afford that amount of model so I press it down and there we go if I look at it on the screen you can see a

Blob of warmth coming in the middle of the heart the other heart doesn't do anything and it reaches in oh it's really getting warm and it goes up to a temperature of about 50 degrees it's somehow producing crystals that come out

Sideways and giving out heat which lasts for 20 minutes or so what happens is when you click a tiny particle of something is released some people say it's a bit of metal others say it's a tiny crystal of sodium acetate that was

Trapped on the metal surface but it doesn't matter you release something and as soon as you have that first kindly nucleus the precipitation takes place and you can see the crystals spreading out across the hand warmer and the

Temperature rising so when you drop crystals of sodium acetate into water they ions separate and because they need energy the temperature of the water drops and you can see quite nicely with thermal

Imaging if you drop sodium acetate crystals into water the water gets cuddle it's getting cold because some of the thermal energy the heat energy in the water is being used to pull these ions

Apart this is a physical change so if they come out of solution reform their crystals you'll get that energy back so the question is how can you get that energy back in your hand warmer the way you've

Got to do it is to get as much sodium acetate as possible dissolved in the water and with sodium acetate if you heat the water up you can dissolve more and more of the salt so if you go almost to the boiling

Point of water hundred degrees centigrade you can dissolve really a large amount what you would imagine that if you dissolve all this stuff up by heating it as soon as you cooled it down you would expect it all to come out

Again but the interesting thing is that crystals cannot just form in a really clean solution they need to have tiny particles doesn't really matter what of tiny bit of metal a tiny crystal to form round it's rather like a crowd forming

Round a single person it has to have something to start it so if you have a really clean filtered solution if you cool it down the sodium acetate stays in solution and that's what's inside your hand warmer so at least your hands will

Be warm when you walk to work in the freezing conditions to reuse the hand warmer you have to heat it up again so we dropped it into boiling water and quite by chance we noticed that there were all sorts of

Interesting bubbles and vortices in the surface of the boiling water so that's what you have to do to finish it off just put it in there leave it for a little while you take it out and let it relax and it gets cooled down and

Remains liquid and if you heat it for a longest time all the sodium acetate re-dissolve and then if you cool it slowly it will be ready to use again the problem is that if you don't heat it long enough

And leave just one or two tiny crystals it can go off spontaneously and suddenly release its heat it's not dangerous but it means when you go to it to warm your hands you'll find it's fired already thanks for watching this video and we'd

Like to thank Google's making and science team for making it possible if you'd like to see more of the videos they've helped create there's a brilliant playlist there's links on the screen and in the description also if

You'd like to see professor polyakov's long-awaited appearance on my objectivity series there are also links for that and we'll be back again soon with more videos with the thermal imaging camera

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