Inside the Glacial Heat exists a supersaturated and super-cooled (below its freezing point) solution of sodium acetate and water.This supersaturated solution was created by mixing the salt (sodium acetate) in hot water. Hot liquid will dissolve more salt than a cold one. When this solution is cooled slowly, the salt stays in solution.
CH3COONa.3H2O + Heat -> CH3COO-(aq) + Na+(aq)+3H2O
A small, stainless steel, metal chip provides the “spark”. When the chip is squeezed, a small, single, solid salt molecule is created. This is the seed ,on which, the other salt crystals begin to form. The normal freezing point for sodium acetate is 130 degrees F (54 degrees C). The reaction occurs quickly, with heat being released and the liquid becomes solid (freezes). The heat being released is equal to the freezing point of the solution (54 degrees C). The sodium acetate (a salt) dissolving and freezing in the water is an example of a physical change.
How do I Teach With Glacial Heat?
Discuss physical and chemical properties:
Physical properties are observable (color, size, luster and smell) and also include characteristics, such as, freezing point, melting point, malleability, conductivity, volume, mass, weight and length.
Chemical properties are only observable during a chemical reaction and can include flammability or the ability to rust. In each of these examples, a new compound has been formed.
Discuss physical and chemical changes:
Physical changes include ice melting, molding clay, water evaporating, a coke freezing and sugar dissolving in water. In these examples, no chemical changes have occurred and the changes can be reversed.
Chemical changes include metal rusting, lighting a match, milk souring and the stomach digesting food. These changes are not easily reversed. The presence of light, color change, odor, gas production, heat or sound can indicate that a chemical change has taken place.
The Glacial Heat can be boiled (melted) for 7-10 minutes and reused over and over again.