Introduction: When a substance undergoes a phase change, heat is either released or absorbed by the substance. Solidification or crystallization involves a phase change from liquid to solid. Heat is released by the substance as it solidifies. The same amount of heat is absorbed by the surroundings. Crystallization, then, is an exothermic process. The heat lost when one mole of a liquid solidifies at a constant temperature is the "molar heat of solidification." When the process of crystallization takes place in a calorimeter, the heat released by the substance that is solidifying is absorbed by the water in the calorimeter. As a result, the temperature of the water increases. This temperature change can be used to determine the heat of crystallization of the substance undergoing the phase change.
Purpose: The student will determine the heat of solidification of a wax sample.
Materials: 25 x 200 test tube, 250 mL Beaker, Ring stand and ring, Hot plate, 100 mL Graduated cylinder, Thermometer, Styrofoam cup, Safety goggles, Wax sample, Balance, Test tube tongs
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