How Does
How Ice Packs Work
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By eHow Contributing Writer
Overview of Ice Packs
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An ice pack is a plastic bag filled with a frozen gel, frozen liquid, ice or another substance capable of maintaining extremely low temperatures for an extended period of time. Ice packs are often stored in a freezer before use, although some ice packs can freeze instantly through a chemical reaction. These instant ice packs are used therapeutically and are useful in emergency situations since they can be transported at room temperature. Many people also use ice packs in coolers to preserve meat, dairy products and other food.
How Ice Packs Work
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Chemical ice packs use an endothermic reaction between water and ammonium nitrate to achieve cool temperatures rapidly. An endothermic reaction occurs when two separate compounds interact to absorb energy in the form of heat. Before it is used, an ice pack contains both water and ammonium nitrate in separate tubes. When these tubes are broken, the water and ammonium nitrate mix, setting off an endothermic reaction and causing the water to freeze. The freezing of the water prevents all of the ammonium nitrate from instantaneously mixing with the water. As the ice melts, the water mixes with additional ammonium nitrate, causing additional endothermic reactions and forcing the melted ice to re-freeze. This process allows ice packs to remain frozen and maintain extremely low temperatures for an extended period, despite being at room temperature.
Uses for Ice Packs
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Ice packs are extremely useful for preserving food, particularly in situations where it is not possible to refrigerate food for long periods. Unlike pure ice, the water from ice packs cannot mix with food and become contaminated. Ice packs are also significantly more efficient that pure ice: four ice packs, when stored with food in a cooler, provide the same chilling power as 10 to 20 pounds of ice. Ice packs are also used extensively by medical professionals in both emergency and nonemergency situations. Ice packs cause muscles to numb and constrict, preventing the muscle from being overworked and allowing it to heal. Ice packs are smaller and much easier to transport than pure ice, making ice packs a favorite tool of physical therapists. Ice packs are also reusable, which makes them more cost-effective than pure ice.
eHow Article: How Ice Packs Work
