Hot ice~

       This week I gonna share a experiment called "hot ice" with you guys~ Let's see the video first~

Wonder what is happening? The experiment just shows an interesting feature of superstation (過飽和). The colorless solution is actually water supersaturated with sodium acetate (醋酸鈉). Most of you probably have heard of supersaturation, which means that there are more solutes (in this case, sodium acetate) than normal in the solvent. Supersaturated solution is not thermodynamically stable but there is no proper way for it to transform into the more stable crystal phase since the energy barrier is too high.


However, once you put a “seed” (or nucleus, 晶種) into a supersaturated solution, the crystal will form rapidly because the seed has decrease the energy barrier considerably (btw this phenomenon is called heterogeneous nucleation).  

  What’s more, the reaction is exothermic—it generates a large amount of heat at the same time. So that’s why it is called “hot ice”! Here’s a video about how hot it could be. Though hilarious, you should take it seriously! (I have no idea why he wanted to put his hand inside it@@ why not just put a thermometer......)

     Never try to do that stupid thing at home, but here's something you can try. Some hand warmers  just make use of this phenomenon. You are supposed to “crush” them before use and them can be reused by putting them into hot water. Interestingly, the crush you do is actually providing a seed for the crystal to grow. By using these hand warmer, you can directly feel the heat produced when forming sodium acetate crystal, in  a more gentle way of course!

reference:

1.http://www.amazingrust.com/Experiments/how_to/Hot-Ice.html

2.https://en.wikipedia.org/wiki/Nucleation

3.https://en.wikipedia.org/wiki/Sodium_acetate