The Heat Solution Instant Handwarmer Thermodynamics Chemistry Demonstration is fun and reusable. If pressure is applied to an activator, a crystal forms in a supersaturated solution of sodium acetate. This causes a solution to crystallize.
A vinyl pouch contains a supersaturated solution of sodium acetate. When pressure is applied to a metal activator, a seed crystal forms in the solution which triggers the entire solution to crystallize. As the solution changes physical state (liquid to solid) it increases in temperature to 130 ºF. The heat will last for over 30 minutes. The vinyl pouch can be easily regenerated and used over and over again.