Cold pack, chemical

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. 

Irritant contact dermatitis is caused by mechanical friction from headbands or wristbands in runners, helmets in football players, gloves and fiberglass in hockey players, and adhesive tape in basketball players (Bergfeld and Taylor 1985 Kantor and Bergfeld 1988). Irritation may also occur after application of medicaments, antiseptics, insect repellants, cosmetics, oily sunscreens, or leakage of cold-pack chemicals (Bergfeld and Taylor 1985 Kantor and Bergfeld 1988). 

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. 

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 a solute dissolves in a solvent, there is an associated energy change, and there is often times a noticeable change in the temperature of the solution. You exploit this phenomenon when you use chemical hot packs or cold packs. This energy change is called the heat of solution or the enthalpy of solution. Formally,... 

One type of cold pack contains a compartment of powder and a compartment of water. When the barrier between the two compartments is broken, the solid dissolves in the water and causes an energy change. What chemical could be used in this type of cold pack Why ... 

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. 

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. 

Endothermic reactions will cool the area around them by absorbing the necessary energy from the surroundings. As the result of an endothermic reaction, the products end up with more potential energy than the reactants. You may be familiar with chemical cold packs. When the chemicals in a cold pack are allowed to mix, they absorb energy from the surroundings to carry out an endothermic reaction. More examples of endothermic reactions are shown here. 

Heat Absorbed Some chemical reactions and physical processes need to have heat energy added before they can proceed. An example of an endothermic physical process that absorbs heat energy is the cold pack shown in Figure 9. 

Cold packs, used by doctors and athletes, lower the temperature of an injury. A cold pack contains two chemicals. The chemicals react with each other when they are mixed. The endothermic reaction absorbs heat from the injured part of the body. It helps to cool the body down. 

Athletes use cold packs that do not have to be frozen. To get the pack to be cold, the athlete smashes the pack on a hard surface. The chemicals inside the pack mix together, causing them to become very cold. 

Cryoanesthesia with a cold pack during combined chemical blepharoplasty (Lip Eyelid ) and TCA to the papillary dermis... 

Both hot and cold packs depend on large energy changes taking place during a chemical reaction. Cold packs rely on an endothermic reaction, and hot packs generate heat energy from an exothermic reaction. 

A spontaneous process occurs by itself, whereas a nonspon-taneous process requires a continuous input of energy to make it happen. It is possible to cause a nonspontaneous process to occur, but the process stops once the energy source is removed. A reaction that is nonspontaneous under one set of conditions may be spontaneous under a different set of conditions. 20.5 The transition from liquid to gas involves a greater increase in dispersal of energy and freedom of motion than does the transition from solid to liquid. 20.6 In an exothermic reaction, A5 r,. > 0. In an endothermic reaction, A5, rr < 0. A chemical cold pack for injuries is an example of an application using a spontaneous endothermic process. 20.8(a), (b), and (c) 20.10(a) positive... 

Chemical cold packs are used for fast relief of pain due to injury. Some chemical cold packs contain two separate compounds that are combined in a process that absorbs heat. Which compound would make the best chemical cold pack ... 

Analyze and Conclude Which is the best chemical for a chemical cold pack ... 

The change in energy is an important part of chemical reactions, so chemists include AH as part of many chemical equations. The heat-pack and cold-pack equations are called thermochemical equations when they are written as follows. 

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. 

Some chemical reactions behave in just the opposite way— they absorb energy from their surroxmdings as they occur. Such reactions are said to be endothermic. The use of a chemical cold pack is a good example of an endothermic reaction. When a barrier separating the reactants in a chemical cold pack is broken, the substances mix, react, and absorb heat from the surroimdings. The surroimdings— possibly including your bruised ankle—get colder. 

Heat absorption or emission, as well as light emission, are also evidence of reactions. For example, a natural gas flame produces heat and light. A chemical cold pack becomes cold when the plashc barrier separating two substances is broken. Both of these changes suggest that a chemical reaction is occurring. 

Some cold packs contain substances that undergo an endodiCTinic physical change rather than a chemical change. 

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