Most hand warmer companies use oxidation to heat their hand warmers. What they do is put a combination of things in their hand warmers and then when it is exposed to oxygen (when you open the package) it heats up. It is because some chain reactions are endothermic reactions and others are exothermic reactions. Hand warmers use an exothermic reaction which makes it heat up because it doesn’t actually give off heat, it just takes all the cold air away so that all that’s left is hot air. An endothermic reaction does the opposite of that which is how they make instant ice, but that’s not using oxidation.

I made some hand warmers and here is the recipe.

Materials:

• Iron filings.
• A closable bag
• salt
• vermiculite                                                             
• Water

Steps

1. Put 25 g of iron filings in a closeable bag.
2. Put 1g of salt in the bag.
3. Shake it for 20 seconds
4. Put 1 tablespoons Of vermiculite into the bag
5. Shake for another 20 seconds
6. Put 5ml of water in the bag