Cold pack

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. 

Heats of solution are the basis for instant cold packs and instant hot packs used for the first-aid treatment of minor sprains and pulled muscles. These packs have two separate compartments. One contains water, and the other contains a salt NH4 NO3 for cold packs and MgSO. or CaCl2 for hot packs. Kneading the pack breaks the wall between the compartments, allowing the salt to mix with water. As the salt dissolves to form an aqueous solution, the temperature of the pack changes. Heat is absorbed or released only as the salt dissolves, however, so after all of the salt has dissolved, the pack gradually returns to room temperature. Further manipulation of the pack has no effect. 

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. 

Explain how a cold pack, often used in emergency or sports medicine, works. 

If extravasation occurs, the infusion should be stopped immediately, with aspiration of fluid from the site, needle, and tubing as much as possible. The affected limb or area should be elevated (if possible). The site should be documented photographically as well as the time, date, site, patient complaints, and estimated volume of extravasated drug.36 Both hot and cold packs have been used to manage extravasations, but use of the proper therapy for certain agents is critical. For example, warm compresses have been shown to worsen doxorubicin extravasations, whereas cold packs may exacerbate vinca alkaloid... 

Anthracyclines Cold packs DMSO 50-99% Alternative Dexrazoxane Apply 1-2 mL to area of skin twice the size of lesion every 6-8 hours for 7-14 days 1000 mg/m2 IV within 5 hours of extravasation followed by 1000 mg/m2 on day 2,500 mg/m2 day 3 Allow to air dry. Do not cover Promising new agent expensive, may not be reimbursed by payors. 

Mechlorethamine Cold packs Sodium thiosulfate Prepare 1/6 M solution by adding 4 mL of 10% solution to 6 mL sterile water inject 2 mL for each mg of mechlorethamine. Follow with 1 mL SQ (0.1 mL doses clockwise around area) may repeat every 3-4 hours if needed. Sodium thiosulfate must be diluted prior to administration. 

Fhclitaxel Cold packs Hyaluronidase As above Hot packs paradoxically shown to worsen lesions in some case reports. 

Educate the patient regarding proper application of hot or cold packs as well as topical antidotes. Should the area be allowed to air dry or be covered ... 

Nonpharmacologic therapies include reassurance and counseling, stress management, relaxation training, and biofeedback. Physical therapeutic options (e.g., heat or cold packs, ultrasound, electrical nerve stimulation, massage, acupuncture, trigger point injections, occipital nerve blocks) have performed inconsistently. 

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. 

Atypical cold pack has two separate chambers. One chamber contains a salt. The other chamber contains water. Crushing the pack allows the salt to dissolve in the water—an endothermic process. 

This person s shoulder was injured. Using a cold pack helps to reduce the inflammation of the joint. 

Some types of hot packs are constructed in much the same way as the cold packs described above. They have two compartments. One compartment contains a salt, such as calcium chloride. The other compartment contains water. In hot packs, however, the dissolution process is exothermic. It releases heat to the surroundings. 

Cold packing of mustard, nutritional liquids for hospitals... 

One common application of thermochemistry in everyday life is the use of hot and cold packs. A variety of these are used to treat injuries and provide warmth. One type of pack used to provide heat utilizes the exothermic oxidation of iron to produce heat. The reaction can be represented as... 

A hot pack is activated when someone initiates the reaction by some physical action such as shaking or breaking a seal on the pack. The actual hot pack reaction involves several other chemicals, but the primary reaction is the oxidation of iron. The iron in the hot pack is a fine powder to increase the efficiency of the reaction. As expected, cold packs depend on some type of endothermic process. One common cold pack is based on the mixing of ammonia nitrate and water. In this case, the heat of... 

When the reaction is initiated by breaking a barrier separating the ammonia nitrate and water contained in the pack, heat is absorbed from the surroundings. The immediate surroundings in this case happen to be the body part to which the cold pack is applied. 

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. 

Carbon dioxide is formed by the action of acids on carbonates and as a by-product of fermentation, the conversion of carbohydrates to ethanol by yeast. Because its triple point is at 5.1 atm, it cannot exist as a liquid at ordinary atmospheric pressure. Solid carbon dioxide, which is sold as dry ice, sublimes directly to the gas—a property that makes it convenient as a refrigerant and cold pack. 

Bassam Z. Shakhashiri, "Chem-tical Cold Pack," Chemical Demonstrations, A Handbook for Teachers of Chemistry, Vol. 1 (The University of Wisconsin Press, Madison, 1983) pp. 8-9. 

Instant cold packs used to treat athletic injuries contain solid NH4NO3 and a pouch of water. When the pack is squeezed, the pouch breaks and the solid dissolves, lowering the temperature because of the endothermic reaction... 

What is the final temperature in a squeezed cold pack that contains 50.0 g of NH4NO3 dissolved in 125 mL of water Assume a specific heat of 4.18 J/(g °C) for the solution, an initial temperature of 25.0°C, and no heat transfer between the cold pack and the environment. 

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