Hot ice refers to the solid state of water formed not by low temperature, but by high pressure, etc.
Why is sodium acetate called hot ice?
The reason why sodium acetate is called hot ice is mainly the crystallization of sodium acetate supersaturated solution.
The cooled sodium acetate supersaturated solution is temporarily metastable. When stimulated (by the addition of solid crystals or by shaking them to produce tiny crystals) the state is out of balance and too much of the solute crystallizes, returning to an equilibrium (a saturated solution) suitable for the temperature at that time. So it's going to give away all the heat above that temperature, and it's going to get hot. Before the experiment, the sodium acetate solution was colorless and transparent, which was very similar to water. And touch it lightly with a small bamboo stick dipped in sodium acetate trihydrate crystals, too much solute as water freezes like rapid crystallization, and crystallization at the same time will give off heat, so called "hot ice."
