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Instructions - E xperiment 8 Dystan Medical Supply...

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Experiment 8 Dystan Medical Supply Company—Cold Packs and Hot Packs IN CHEM S125 1705 EXP CHEMISTRY I HONORS Introduction Hot and cold packs are used to treat injuries in the hospital to minor injuries at home. For example, cold packs are used to keep a patient’s body temperature down when they become deathly hot or to decrease inflammation in a sprained ankle. Hot packs can be used to reduce muscle spasms, muscle soreness, inflammation, and relieve pain. Since the demand for hot and cold packs is so great, companies like Dystan Medical Supply produce and sell cold and hot packs in large quantities. These packs are made by dissolving salts in water. When an ionic compound dissociates in water it either absorbs energy from the water or releases energy to the water. When the compound absorbs energy, it does so through heat energy. This is an endothermic process. An Exothermic process would be one in which energy is released to the surroundings. In this case hot packs are exothermic and cold packs are endothermic. In general a pack is created by using a plastic bag which has a compartment of water and a compartment of salt. The bag is broken and the two mix either absorbing or emitting heat. The amount of heat depends on the salt’s concentration in the water.1 In chemistry, calorimeters are constructed to find the enthalpy of reactants and calculate the heat evolved. At constant pressure the enthalpy is the heat gained or lost by a system. A calorimeter is a device that is a closed system. Therefore, no energy can enter the system, so any change in temperature is due to the substances within the calorimeter. For this experiment, water was the substance that is put into the calorimeter and then a salt was added and the initial and final temperatures were recorded. However, a calorimeter is not perfect; therefore it must first be calibrated by having a known amount of substance at a known temperature and adding the same amount of the same substance at a different temperature. In this manner you can find the heat capacity of the calorimeter, which is the amount of heat needed to raise its temperature by 1 degree Kelvin. Once the calibration is done the change in temperature can be recorded and the heat evolved or heat needed for the reaction (heat of reaction) can be determined if the specific heat of, in this case, water is known. Specific heat is the amount of heat required to raise one gram of a substance by
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one degree Celsius and heat evolved is moles times the molar heat of dissolution. Since the moles can be measured it would be possible to calculate the molar heat of dissolution, which is the change in heat when a solute is dissolved. A change in heat occurs because in dissociation the bonds between the ionic molecules are broken apart. In some cases more energy is needed to break apart these bonds than the amount of energy that is gained from the breaking of the bonds. This would mean the system would have to take energy from
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Instructions - E xperiment 8 Dystan Medical Supply...

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