How does a chemical heat pack works?

Answer 1

Most of the heatpacks contain supersaturated solution of sodium acetate that heats up when the crystallization process is started by flexing a metal disc embedded in the liquid. Since the liquid is supersaturated (concentration of a solution beyond saturation point), flexing the notched ferrous metal disc makes the solution crystallize suddenly, thereby releasing the energy of the crystal lattice.

The triggered effect of the solution will generate heat for up to 45 minutes before it will begin to cool back to room temperature. The heat pack can be reused once the sodium acetate is dissolved back to a liquid state done by simply placing the heat pack in a pot of boiling water for 10-15 minutes.

Once the heat pack has returned to room temperature it can be activated again with the metal disc. Easy as 1-2-3 to use and reuse!

To Activate Heat Pack:

1. Flex metal disc back and forth inside the heat pack until crystals form.

2. Knead crystals inside the heat pack to soften during activation process.

3. Apply heat pack to desired area.

To Reuse Heat Pack:

1. Carefully place the hardened heat pack on a cloth in a pot of boiling water.

2. Boil in rolling water for 12 - 15 minutes until all crystals are gone.

3. Let the heat pack cool to room temperature before using again.

Be sure to read all instructions and warnings on packaging before use.

You can also watch video for the heat packs .

Answer 2

Rust, for some types and crytalisation for some others.

Oxidizing iron (rust) generates the energy that is expressed as heat in some chemical heat packs.

Oxidizing is one term for burning, rust is just a very very slow fire.

Some other chemical heatpacks use a salt (often sodium acetate which is also used as a spice, tastes like salt & vinegar mixed together)

In these crytalization releases the energy in the solution. This kind is reusable, heat them till the crystals melt, the cool them slowly.