Sodium Acetate 

Crystallization and Heat Release:
Triggering crystallization: Introducing a "seed crystal" of sodium acetate trihydrate (the solid form) disrupts the stability. This triggers a rapid crystallization process throughout the solution.

Exothermic reaction: Crystallization releases heat, known as the heat of crystallization. This is why the solution suddenly feels hot, reaching up to 54-58°C, even though it started cold. This phenomenon is often called "hot ice."

Applications:
Instant "freezing" trick: This principle is used in magic tricks where seemingly touching the supercooled solution instantly "freezes" it.
Hand warmers: Reusable hand warmers are often filled with a supercooled sodium acetate solution. Clicking a metal disk inside initiates crystallization, releasing heat to warm your hands.
Safety:
Your eyes.

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