What Are the Ingredients in an Ice Pack?
As part of any basic first aid kit, medical "ice packs" are meant to reduce swelling and alleviate pain resulting from an injury. Despite its ubiquitous nature, few people know what ingredients are used in these ice packs that makes them so cold so quickly. Knowing the ingredients of an ice pack and the way that they interact can help you understand how to properly use an ice pack in case of an emergency.
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Amonium Nitrate
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Often used as a fertilizer, amonium nitrate (NH4NO3) is an ionically-charged compound that requires the addition of another, non-ionic compound to create a cold sensation. This is a hallmark of ice packs.
Water
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Water (H2O) is a non-ionic compound that interacts with ammonium nitrate to create "cold."
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Creating "Cold"
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Ammonium nitrate and water interact in an endothermic reaction. Endothermic reactions require heat from an outside source to occur and so pull the energy of outside molecules to fuel the reaction. The result is a "cold" sensation when the ice pack is touched.
Alternative Ionics
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An alternative ionic compound used is Ammonium Chloride (NH4CL) is another common ingredient in newer generations of ice packs; the endothermic reaction with water is stronger, but the effect is shorter in duration.
Construction
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A chemical ice pack contains a small glass vial of the ionic solution suspended in a sealed pouch filled with water (or a water-laden gel). The user breaks the glass vial, causing the reaction to start.
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