Instant ice packs are a good first aid solution to sprains, strains, and other minor injuries and thus are included in most first aid kits available today. But the way that ice packs generate cold so quickly, or how they are able to be stored at room temperature for so long, often remains a mystery to most consumers. Understanding the chemicals used in chemical ice packs will allow you to use them safely and effectively in an emergency.
Ammonium Chloride (NH4CL) is a common ionic compound used in chemical ice packs to react with a non-ionic compound to create that "cold" sensation.
Alternate ionic compound
Ammonium Nitrate (NH4NO3) is used in older chemical ice packs, but interacts with the non-ionic compound in the same manner. Ammonium Nitrate is also used as a common chemical fertilizer.
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Water (H2O) is the non-ionic compound used in both kinds of chemical ice packs. Water is both safe and common, thus making an ideal non-ionic compound for ice packs
When the ionic and non-ionic compounds come in contact, an "endothermic" reaction takes place which uses energy (in the form of heat) from the surrounding atmosphere, creating a "cold" sensation.
Typically, a small amount of the ionic compound is placed in a thin glass vial and suspended in a water solution (or water-laden gel) inside of a sealed pouch. The user breaks the vial causing the reaction but because it is sealed, the reaction is less likely to cause harm to users.