Several components in a plastic bag are exposed to water. Upon mixing, a slow and steady evolution of heat occurs due to the oxidation of iron and reduction of oxygen in the presence of sodium chloride and calcium chloride catalysts.
Curriculum Connection: Grade 10 Chemistry, Academic and Applied; Grade 11 and 12U Chemistry
5 Bags containing Iron Powder, Sodium Chloride, Calcium Chloride and Vermiculite
Safety Goggles, Gloves, Lab Apron
- Put on your safety goggles and other safety equipment.
- Obtain one bag containing iron powder, sodium chloride, calcium chloride, and vermiculite.
- Add 10mL of distilled water to the bag and reseal i
- Squeeze and shake the bag to thoroughly mix the contents.
- Observe any changes in the bag over time.
Commercial heat packs take advantage of exothermic reactions. Though there are a couple of different reactions that heat packs may use, the most common is the oxidation of iron. Oxidation of iron is a slow reaction that generates a very small amount of heat. In order to increase the heat generated, a heat pack contains catalysts, usually some type of salt. A catalyst is something that speeds up a reaction. The oxidation of iron also requires oxygen. For this reason, heat packs are stored in sealed bags which do not allow oxygen to enter until opened.
When the heat pack is removed from the bag, it is squeezed and shaken to mix the ingredients. One more factor that enhances the reaction is water. The materials in the heat pack are moist. When removed, the iron, moisture, catalyst, and oxygen are all allowed to interact, starting an exothermic reaction that results in the noticeable production of heat in the area surrounding the heat pack.
Dispose of iron powder in accordance to state and local regulations
James Palcik is the owner of Palcik Educational in Ancaster, Ontario. This activity is from the Whiz, Bang, Boom Demos for Science conference session, delivered by James at STAO 2012. Activity from Innovating Science TM by Aldon Corporation, copyright 2008. Used with permission of Palcik Educational.