My favorite exothermic reaction!

      After a long, cold season of marching band, I've grown a great appreciation for hand and feet warmers! With a great amount of time spent at football games every week, I began to wonder about the chemistry behind these wonderful heat packets. Heat packets contain a mixture of iron powder, salt, water, and activated carbon. When released from their air sealed packaging, the plastic permeable membrane allows oxygen into the packet starting the chemical reaction. This mixture of substances in addition to oxygen produces iron oxide with heat as a bi-product explaining the heat we receive from the packet. Manufacturers of heat packets may manipulate the production of heat by manipulating the amount of the substance in the packet and the actual material of the packet. For instance, increasing the mixture within a packet increases the duration of the heat since more reactants result in more bi-products, one being heat. The permeability of the packet also determines how fast or slow heat is produced since more or less oxygen is let in limiting or increasing the reactants consequently increasing or decreasing the speed of the reaction. Manufacturers are now looking for more applications of products such as these.
Learn more from this article: https://pubs.acs.org/cen/science/88/8804sci3.html
      I love heat packets even more now knowing how they are a prime example of how chemistry can be used as an application in life. More importantly, it's interesting how this chemical reaction can directly be changed so easily. For example, simple changing the material of the packet determines the speed the reaction takes place in proportion to the amount of oxygen let in. Also manipulating the actual contents of the mixture in a packet can change the amount of heat produced. Though heat is technically the bi-product of this reaction that produces iron oxide, it is the product that every buyer wants in reality. Even though this is not a life-changing application, it is interesting to see how the basics of chemistry can be used in everyday life without being recognized.