Heat therapy has become standard treatment for ailing muscles among athletes, the disabled and elderly people. Heat packs provide relief by dilating the blood vessels of nearby muscles and allowing the soft tissue to stretch, and cold packs reduce the swelling and inflammation of injured body parts. Chemical advance have led to the development of very convenient types of heat packs and cold packs, which can now be found in most emergancy first aid kits.
Hot Packs
There are number of types of chemical heat packs used. Some packs consist of two plastic bags, the inner bag contains water, and the area between the inner bag and the other bag is filled with a dry salt. When the inside bag is broken, the solid and the water react in an exothermic reaction, releasing heat. However, the most frequently used heat packs today involve one sealed plastic pouch containing a metal disk and salt solution; commonly calcium chloride, magnesium sulfate, or sodium acetate.
Cold Packs
A cold pack comes in a plastic bag made of tough white plastic. This bag is filled with a smaller bag and ammonium nitrate crystals. The smaller bag contains water, and is made of a thin weak plastic, so it easy to break. When a cold pack is used, it must be "broken" by rupturing the inner bag. Braking the bag releases the water, which dissolves the ammonium nitrate.
The water and ammonium nitrate react completely, and within fifteen to twenty the cold pack will no longer feel cold.
Cold packs make use of the heat transfer that occurs during chemical reactions, but is contrast to heat packs, utilize endothermic reaction. In the endothermic reaction between ammonium nitrate crystals and water 💦, the heat required for the reaction to proceed from reactants to products is absorbed from the surroundings environment, resulting in a decrease in temperature 🌡️ of pack noticeable to the touch.
