Hot packs are used for treating injuries and for warming hands and feet during cold weather. Heat packs promote the increase of blood to damaged areas and cold packs decrease the flow. Cold packs are also used in injuries for shrinking bruises and also for chilling food and liquids. Hot packs are composed of magnesium sulfate or calcium chloride. Cold packs are full of ammonium nitrate. Both packs have a section of water separated from the chemicals. They normally maintain their temperatures for approximately 30 minutes.
When a cold pack is crushed, the thin plastic layer separating the chemicals from the water is breached. The chemicals and the water mix together, with the ammonium nitrate producing an endothermic reaction. Endothermic reactions involve the absorption of heat. The ammonium nitrate mixing with the water creates cold. The temperature of cold packs can reach a low of 32 degrees F.
When a hot pack is crushed, the plastic layer keeping the water away from the chemicals is broken. The water and chemicals mix together to produce an exothermic reaction. Exothermic reactions create heat through the mixing of water and the calcium chloride or magnesium sulfate. Hot packs can reach temperatures of 194 degrees F.
Hot packs and cold packs be used in numerous ways. Hot packs can be placed on backs to ease muscle pulls and cramps. Cold packs can be used for chilling food and drink as well as for alleviating body aches and pains. When either pack is used, it is recommended that a layer be used in between the pack and bare skin. Cold packs and hot packs can generate temperatures that are painful if the packs are placed directly on the skin; direct placement on the skin is also potentially dangerous (e.g., scalding from heat, sticking to skin from cold).
