Heat packs

A skier is trapped by a sudden snowstorm. After building a snow cave for protection, she realizes her hands and feet are freezing she is in danger of frostbite. Then she remembers the four small packs in her pocket. She removes the plastic cover from each one to reveal a small paper packet. She places one packet in each boot and one in each mitten. Soon her hands and feet are toasty warm. 

These magic packets of energy contain a mixture of powdered iron, activated carbon, sodium chloride, cellulose (sawdust), and zeolite, all moistened by a little water. The paper cover is permeable to ait 

The exothermic reaction that produces the heat is a very common one—the rusting of iron. The overall reaction can be represented as 

The oxidation of iron by oxygen occurs naturally. Any steel surface exposed to the atmosphere inevitably rusts. But this oxidation process is quite slow—much too slow to be useful in hot packs. However, if the iron is ground into a fine powder, the resulting increase in surface area causes the reaction with oxygen to be fast enough to warm hands and feet. The packet can produce heat for up to six hours.  

Metal hydrides are discussed in A much better alternative seems to be the use of metals that absorb hy- 

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Organic Carbon. The total organic carbon (TOC) in a water sample is determined by injecting a microliter sample into a heated, packed tube in a stream of oxygen. The water is vapori2ed and carbon is converted to carbon dioxide, which is detected with a nondispersive infrared analy2er. 

In a microwave-heated packed catalyst bed, two different forms of hot spots can be created. 

Thomas JR, Faucher FJ (2000) Thermal modeling of microwave heated packed and fluidized bed catalytic reactors. Microw Power Electromagn Energy 35 165-174... 

PAD HEAT TREATMENT INSTANT HEAT PACK KWIK HEAT BECOMES 110 DEG 4 6530013813648 PG 14.22 ... 

Chlorination in shaft electric furnaces. A shaft furnace is a steel apparatus lined on the inside with a layer of diabase on liquid glass and a layer of special low porosity chamotte brick. The lower part of the furnace has two rows of coal electrodes (three in each row). The lower part of the furnace is filled with coal packing to 400-700 mm above the top electrodes. The melted metal chlorides flow down the heated packing. They are collected in the lower zone of the furnace and periodically unloaded. 

Q A heat pack can be used to supply heat to injuries. One type of heat pack is re-usable. It contains a supersaturated solution of a salt and a disc of metal. When the metal disc is bent, the solute begins to crystallize and releases heat. The pack can be reset by heating it in boiling water, which causes the salt to dissolve again. How can you account for the heat that is released by this kind of pack ... 

Burning isn t the only exothermic reaction. There are, for example, emergency heating packs used by mountain rescue people that depend on an exothermic reaction. They contain two chemicals that react exothermically when the barrier between two containers of chemicals is broken. Isn t it dangerous carrying chemicals like that about Not really, because the chemicals are iron and water and the reaction is rusting - but in this case a third chemical is added as a catalyst to speed up the reaction so that the heat is given out much more quickly than normal. 

Hypothesizing One type of heat pack contains fine iron particles. These packs are kept in a sealed container and release heat when they are exposed to air. How does this type of pack work ... 

Think about what happens when you warm yom hands on a cold day by using a heat pack similar to the one shown in Figure 16-6. When you remove the plastic wrap, oxygen from the air enters the pack. The oxygen reacts with iron in the pack in an exothermic reaction described by the following equation. Note that energy is shown as a product of the reaction, which means that heat is released. 

What kind of energy transfer occurs during the exothermic heat-pack reaction Heat produced by the reaction flows from the heat pack (the system) to yom cold hands (part of the surroundings). 

The sign of the enthalpy of reaction Recall the heat-pack reaction of iron with oxygen. 

According to the equation, the reactants in this exothermic reaction lose heat. Therefore, //products < reactants- When //.eactants is subtracted from the smaller //products negative value for is obtained. Enthalpy changes for exothermic reactions are always negative. The equation for the heat-pack reaction and its enthalpy change are usually written hke this. 

The equations for the heat-pack and cold-pack reactions that you learned about in Section 16.2 are called thermochemical equations when they are written like this. 

In Figure 16-16, you can see a familiar picture of what happens to an iron object when it s left outdoors in moist air. Iron rusts slowly according to the following equation. It s the same chemical reaction that occurs in the heat pack you learned about earlier in the chapter. 

The heat pack goes into action the moment you activate it by ripping off the plastic covering. Similarly, unprotected iron objects rust whether you want them to or not. 

Gas-liquid-solid Slurry CSTR with jacketed cooling/heating Packed bed with downflow, upflow, or countercurrent... 

Reading Heat Packs and Cold Packs 13 1 1.3. THE CONDUCTIVITY OF SOLUTIONS. . . 14 1 1 The Preparation of Dilute Solutions 42... 

Heat packs are used for first aid purposes. There is a supersaturated solution of sodium acetate (NaCH3COO) in a packet. 

Heat packs Packs used for first aid purposes by giving off heat. 

Slow Release Other materials also combine with oxygen but release heat so slowly that you cannot see or feel it happen. This is the case when iron combines with oxygen in the air to form rust. The slow heat release from a reaction also is used in heat packs that can keep your hands warm for several hours. Fast and slow energy release are compared in Figure 8. 

Most solutions do not exhibit ideal behavior, and the actual curve corresponding to the variation of the molar volume or enthalpy of the mixture deviates from a straight line (e.g., the solid line in Fig. 5.1). When the curve for the molar volume lies above the ideal mixture line, the system expands upon mixing when the curve lies below the line, the system contracts. In the case of the molar enthalpy, a curve that lies above the ideal mixture line corresponds to the system that absorbs heat (e.g., mixing lead bromide and water) a curve that lies below the line corresponds to the system releasing heat (e.g., mixing sulfuric acid and water). This non-ideal mixing in the case of the molar enthalpy is the principle used in cold packs and heat packs. We will develop mathematical models to describe non-ideal mixtures. We use partial molar properties in more detail later. 

Heat packs sometimes contain a solution of sodium acetate trihydrate cooled below its freezing point. When the pack is activated, the compound freezes very rapidly, releasing the heat that had been stored in its supercooled phase. 

In heat packs to relieve stiffness and pain, to keep hands and feet warm, and to warm baby bottles ... 

The reaction that occurs in the heat packs used to treat sports injuries is 4Fe(s) + 302(g) 2Fe203(s) AH = -1652 kJ... 

The overall reaction in commercial heat packs can be represented as... 

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