You want more heat??!

In January 2014, Uncategorized on January 29, 2014 at 4:12 pm

kirsti hot ice heat packB

Kirsti: Me compiling a post about heating my body up after some mighty heatwaves across Australia might seem somewhat of a surprise.

You may even wonder whether I may be lacking thermoregulatory capacities. Well, it’s true. I do lack them. I have pretty low blood pressure and to say my extremities get cold easily is the understatement of the year.

So mid-summer, post-heatwave, I bought some heat packs (yes, I realise this is a dodgy internet site). As you do.

In fact I bought a pack of those reusable awesome sodium acetate or ‘hot ice’ packs. I love the fact that there is a chemical reaction I can WATCH as my heat pack prepares itself to warm my tootsies in bed. Who doesn’t want some chemistry before bed!?!

This heat pack is a nice demonstration of how a super saturated solution behaves essentially under every day conditions, but having been treated with some interesting processes before I got my hands on it.  To be honest, initially I struggled with understanding exactly HOW this thing works. Now, I think I’ve worked it out…..with some help [thanks Chris Thompson!].

Inside my little pack is sodium acetate in a supersaturated solution. That is, the sodium acetate has been heated to some temperature at which you can dissolve much more of it than if it was at room temperature; kinda like how you can dissolve more sugar in hot water than you can in cold water.  Then if you cool it gently, it will stay saturated, and stay in a liquid state.  So sitting pretty with way more molecules of itself than it knows what to do with, when I click a little concave steel disc inside the pack, it creates friction – a fairly violent event – in the solution. This then becomes a nucleating site for crystallisation to occur. Crystals grow outward from the disc, and because it is an exothermic reaction, as it becomes a solid and appears as ‘ice’ crystals, it heats to around 54-57oC. The heat will eventually dissipate and then I can melt the crystals back into their solution to once again anticipate warming my tootsies tomorrow night.

Watch the reaction here.

Thank you sodium acetate for also heating my feet when I’m camping without me waiting for the billy to boil…..


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