Welcome to Brainstuff from how stuff works dot com where smart happens. Hi. I'm Marshall Brain with today's question, how do sodium acetate heat pads work? Sodium acetate heat pads are fun to watch. You start with a pouch of clear liquid. Bending a little metal disk inside the pouch starts the crystallization process, and you can see the crystallization proceed through the liquid. The liquid becomes a solid in a few seconds and its temperature rises to about a d thirty degrees fahrenheit. The process can be understood if you think about water freezing. Water freezes at thirty two degrees fahrenheit, but it's possible to super cool the water. That is, you can get the water's temperature to maybe five or ten degrees below the freezing point without it crystallizing into a solid. You can sometimes do do this using a very clean container and distilled water, so there are no points for the water to begin crystallizing. In this condition, if you tap on the glass, the temperature of the water will jump up to thirty two degrees fahrenheit and the water will solidify very quickly. A sodium acetate heat pad contains sodium acetate and water. It turns out that sodium acetate is very good at super cooling. It freezes at a thirty degrees fahrenheit, but it's happy to exist as a liquid at a much lower temperature, and it's extremely stable as a super cooled liquid. Clicking the disk, however, has the ability to force a few molecules to flip to the solid state, and the rest of the liquid then rushes to solidify as well. The temperature of the solidifying liquid jumps up to a hundred thirty two degrees fahrenheit in the process. When you boil the solid, you melt it back to the liquid state. You have to completely out every crystal in the pouch, by the way, or the liquid will quickly resolidify. You can repeat this cycle forever, theoretically, just as you can freeze and melt water as many times as you like. Do you have any ideas or suggestions for this podcast? If so, please send me an email at podcast at how stuff works dot com. For more on this and thousands of other topics, go to how stuff works dot com and be sure to check out the brain stuff blog on the how stuff works dot com home page.

Welcome to Brainstuff from how stuff works dot com where smart happens. Hi. I'm Marshall Brain with today's question, how do sodium acetate heat pads work? Sodium acetate heat pads are fun to watch. You start with a pouch of clear liquid. Bending a little metal disk inside the pouch starts the crystallization process, and you can see the crystallization proceed through the liquid. The liquid becomes a solid in a few seconds and its temperature rises to about a d thirty degrees fahrenheit. The process can be understood if you think about water freezing. Water freezes at thirty two degrees fahrenheit, but it's possible to super cool the water. That is, you can get the water's temperature to maybe five or ten degrees below the freezing point without it crystallizing into a solid. You can sometimes do do this using a very clean container and distilled water, so there are no points for the water to begin crystallizing. In this condition, if you tap on the glass, the temperature of the water will jump up to thirty two degrees fahrenheit and the water will solidify very quickly. A sodium acetate heat pad contains sodium acetate and water. It turns out that sodium acetate is very good at super cooling. It freezes at a thirty degrees fahrenheit, but it's happy to exist as a liquid at a much lower temperature, and it's extremely stable as a super cooled liquid. Clicking the disk, however, has the ability to force a few molecules to flip to the solid state, and the rest of the liquid then rushes to solidify as well. The temperature of the solidifying liquid jumps up to a hundred thirty two degrees fahrenheit in the process. When you boil the solid, you melt it back to the liquid state. You have to completely out every crystal in the pouch, by the way, or the liquid will quickly resolidify. You can repeat this cycle forever, theoretically, just as you can freeze and melt water as many times as you like. Do you have any ideas or suggestions for this podcast? If so, please send me an email at podcast at how stuff works dot com. For more on this and thousands of other topics, go to how stuff works dot com and be sure to check out the brain stuff blog on the how stuff works dot com home page.