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1.4.HotPacks.ColdPacks (1)

1.4.HotPacks.ColdPacks (1) - HOT PACKS COLD PACKS AND HEATS...

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1 LEARNING OBJECTIVES The objectives of this experiment are to . . . soln use the MicroLab interface to measure the heats of solution ( H , in kJ/mol) of several salts. f calculate the heats of formation ( H , in kJ/mol) of single aqueous ions. predict the heats of solution of additional salts. design a hot pack and a cold pack for specified temperature changes. BACKGROUND All chemical reactions and many physical processes are accompanied by the absorption or release of heat. Your body temperature of 37 °C is maintained by heat released from chemical reactions occurring inside of cells. Sometimes it is medically desirable to temporarily increase or decrease the temperature of a certain body part, such as in the treatment of sprains or bruises. These temperature changes can be achieved with commercially available hot packs or cold packs in which the dissolving of a salt in water either generates or absorbs heat. In this experiment you will measure the heat changes which occur when various salts are dissolved in water and use that information to design both a hot pack and a cold pack capable of producing specified temperature changes. Measuring heats of solution soln The heat of solution, H , is the heat that is generated or absorbed when a salt is dissolved in water and soln is expressed in kJ/mol solute. H is negative for an exothermic solution process and positive if it is endothermic. Thermochemical equations for the solution process are commonly shown as follows: soln KCl (s) –> K (aq) + Cl (aq) H = +17.5 kJ/mol (1) + - soln The experimental measurement of H is done in a calorimeter. For our experiment, the calorimeter will consist of two nested styrofoam cups containing 100 grams of water, a magnetic stirring bar, and a temperature probe inserted through a styrofoam lid. Five grams of a salt will be added and the temperature change of the resulting solution measured.
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