Hot and Cold

With the frigid weather that comes with the holidays, I decided to pick a, well, warmer topic. And what is a better topic than what I use, or something similar anyway, for marching band! Which, just for the record, is every bit as fun as it is cold! But these hot pack things, as I call them, are really wonderful. Some heat packs are single use, but the ones in the following article are multi-use.

Before you open a package, you need to know what’s in them. They are what’s considered a closed system. That means that everything needed for the reaction to occur and reset itself is inside the pack. In these reusable packs, there is a metal disk and gel. the gel is usually sodium acetate in water or another different supersaturated solution. One article states, “The salt – sodium acetate in this case – can be forced to dissolve even after saturation occurs by heating the solution. When brought back to room temperature, the sodium acetate does not return to its solid state, but creates a clear gel. Since the water is now holding a greater load of salt than it would otherwise accept, the resulting solution is very unstable. This is known as supersaturation.” As my chemistry class is currently learning about electrons and configuration, I thought this tidbit about being unstable was relevant. The metal disk breaks the unstable solution apart. The disk itself is concave, and snaps back and forth when pressure is applied. This snapping starts a reaction throughout the entire solution, which causes the salt to crystalize. One site states it best: the salt creates “…a lattice of solid sodium acetate that turns the gel inside the pack opaque. Heat is the byproduct of this reaction…When sodium acetate dissolves in water it dissociates, meaning the sodium ion separates from the rest of the molecule. The salt is willing to dissociate up until the solution is saturated, at which point extra energy in the form of heat has to be added to force the sodium ion away.” The higher the temperature of the solution becomes, the more slat that is dissolved, which, at the same time, can absorb more heat energy. Once the sodium acetate form crystals, more heat energy is released, enough to dissolve the solid. The heat pack can then be boiled in water again until clear gel appears. This means it is supersaturated again, and is ready for use.

I play a lot of sports in addition to marching band, and using it on muscles, or to warm up, makes this a great item. Even if it wears out over time, this product is still worth the price, as it can only help you in the long term.


So ta ta for now and I hope to see your chemical reactions soon!


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