Ammonium nitrate cold packs

The cold pack contains two separate compartments one with ammonium nitrate and one with water. 

A process that releases heat into the surroundings is called an exothermic process. Most common chemical reactions—and all combustions, such as those that power transport and heating—are exothermic (Fig. 6.8). Less familiar are chemical reactions that absorb heat from the surroundings. A process that absorbs heat is called an endothermic process (Fig. 6.9). A number of common physical processes are endothermic. For instance, vaporization is endothermic, because heat must be supplied to drive molecules of a liquid apart from one another. The dissolution of ammonium nitrate in water is endothermic in fact, this process is used in instant cold packs for sports injuries. 

Many of the cold packs sold in stores use this endothermic process. A cold pack usually contains a flimsy plastic bag of solid ammonium nitrate inside a larger package filled with water. When punched, the inner bag ruptures. This releases the ammonium nitrate, which dissolves and produces a chilled pack to relieve pain and swelling in aching joints. 

An instant ice pack for first-aid treatment uses the endothermic nature of the dissolution of an ionic salt in water to provide cold therapy. Two typical materials that absorb heat as they dissolve in water are ammonium nitrate and ammonium chloride ... 

Manufacturers take advantage of endothermic dissolution to produce cold packs that athletes can use to treat injuries. One type of cold pack contains water and a salt, such as ammonium nitrate, in separate compartments. When you crush the pack, the membrane that divides the compartments breaks, and the salt dissolves. This dissolution process is endothermic. It absorbs heat for a short period of time, so the cold pack feels cold. Figure 5.8 shows how a cold pack works. 

Commercial cold packs work by the same principle. Instead of sodium chloride, however, these packs are made with ammonium nitrate, which absorbs much more energy as it dissolves in water. In order for the pack to be activated, it must be punched. As discussed in Section 9.6, this breaks an inner seal and allows the ammonium nitrate to mix with water. As the ammo-... 

We can therefore report that AH = —208 kj because the enthalpy of the reaction mixture decreases by 208 kj in this reaction (Fig. 6.16). An endothermic process absorbs heat, so when ammonium nitrate dissolves in water—as occurs when a cold-pack is used—the enthalpy of the system increases (Fig. 6.17). Note that AH < 0 for exothermic reactions, whereas AH > 0 for endothermic reactions. 

Commercial cold packs and hot packs are available for treating athletic injuries. Both types contain a pouch of water and a dry chemical. When the pack is struck, the pouch of water breaks, dissolving the chemical, and the solution becomes either hot or cold. Many hot packs use magnesium sulfate, and many cold packs use ammonium nitrate. Write reaction equations to show how these strong electrolytes break apart in water. 

Hot and cold packs create aqueous solutions of a soluble salt. A salt such as ammonium nitrate is used in the cold pack and heat is absorbed as the salt dissolves in the water. Hot packs release heat when a salt such as calcium chloride dissolves in the water. 

The athletic trainer in Figure 16-7 can cause this reaction to occur in a cold pack by breaking a membrane in the pack and allowing ammonium nitrate to mix with water. When the cold pack is placed on an injured knee, heat flows from the knee (part of the surroundings) into the cold pack (the system). 

Heat is absorbed when ammonium nitrate dissolves in water in a cold pack. In this photograph, heat is transferred from the injured knee to the chemical process. 

The heavy plastic cold pack holds ammonium nitrate and water. The two substances are separated by a plastic divider. When you squeeze the bag, you break the divider so that the ammonium nitrate dissolves in the water. The dissolving process absorbs heat energy, which must come from the surrounding environment—the surrounding air or your skin after you place the pack on the injury. 

Figure 9 The heat energy needed to dissolve the ammonium nitrate in this cold pack comes from the surrounding environment.

Solid ammonium nitrate, NH4NO3, dissolves in water in a very endothermic process, absorbing heat from its surroundings. It is used in instant cold packs for early treatment of injuries, such as sprains and bruises, to minimize swelling. 

When hot or cold packs for sports injuries are activated, a solute that dissolves exothermically in the case of a hot pack, or endothermically in the case of a cold pack, dissolves in water. Hot packs generally use calcium chloride, CaCb, and cold packs generally use ammonium nitrate, NH4NO3. 

Endergonic changes can lead to a transfer of heat from the surroundings. Cold packs used to quickly cool a sprained ankle are an example of this kind of change. One kind of cold pack contains a small pouch of ammonium nitrate, NH4NO3, inside a larger pouch of water. When the cold pack is twisted, ammonium nitrate is released into the water, and as it dissolves, the water cools (Figure 7.14). 

Organic nitrates (eg, nitroglycerin, isosorbide dinitrate, and isosorbide mononitrate) are widely used as vasodilators for the treatment of ischemic heart disease and heart failure. Organic nitrates such as nitroglycerin are also used in explosives. Bismuth subnitrate, ammonium nitrate, and silver nitrate are used in antidiarrheal dmgs, cold packs, and topical bum medications, respectively. Sodium and potassium nitrate and nitrite are used in preserving cured foods and may also occur in high concentrations in some well water. Butyl, amyl, ethyl, and isobutyl nitrites are often sold as room deodorizers or liquid incense and are sometimes inhaled for abuse purposes. 

Place 0.2 g of solid ammonium nitrate, NH4NO3, weighed on a beam balance (Laboratory Methods C), in a 10 x 75-mm test tube. Hold the test tube in the palm of your hand, and add about 5 drops of distilled water with stirring to dissolve the NH4NO3 (Laboratory Methods K). Describe what you feel and what happens in TABLE 38.IB. A chemical cold pack takes advantage of this behavior of NH4NO3 in water. 

Gunpowder is a compound made by mixing potassium chloride, KCl, found in low-fat salt, with nitrate from ammonium nitrate, NH NOj, found in the cold pack from a first aid kit. 

Ammonium nitrate (NH4NO3) dissolves in water with an endothermic heat of reaction of 26.4 kJ mol. How much ambient heat will be absorbed when 2.0 kg of ammonium nitrate dissolves in water (This reaction is utilized in instant ice packs for treating injuries. Solid ammonia nitrate is contained inside a thin-walled plastic bag, which is sealed inside a thicker bag that also contains some water. The inner bag can be broken by pressing the outer bag, thereby allowing the ammonium nitrate to form a solution with the water which gets quite cold.)... 

Endothermic reactions are much less common. The endothermic dissolution of ammonium nitrate in water is the basis of the instant cold packs that are included in some first-aid kits. They consist of a plastic envelope containing water dyed blue (for psychological reasons) and a small tube of ammonium nitrate, which is broken when the pack is to be used. 

Instant cold packs used to ice athletic injuries on the field contain ammonium nitrate and water separated by a thin plastic divider. When the divider is broken, the ammonium nitrate dissolves according to the endothermic reaction ... 

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