A Practical Energy Experiment or Lecture Demonstration Too often in designing freshmen chemistry experiments, the use of sophisticated equipment and detailed procedures overshadows the basic concent a t the core of the exercise. For our nonscience maim chemistrv, lab.. we have utilized a simple practical crperimmt t o d m m a r i ~ ethe ~ n e r p - r e n a p ~ r a t urelatwnship rc and phase changes. All that 1s requrred are tuo heaarrs, rwo thernmnrrrrs. one eraduatrd cvlinder and ii hot plate. The exprr~mentis brief: the rciulti arc excellent. \Vc h a w cuuplrd thus expermmt to une un ralurrmetr). tincluding hentr id fusim end hems ol~olutirm, allot which can be done inone 3-hr period. Temperature-A Measure of the Concentration of Heat Energy Take two identical beakers. Fill one with 50 ml of water. the other with 100 ml of water. Record the t e m ~ e r a t u r eof each. Place hoth heakcrsoo the same hot platesrmultsnewsls thoth heakersshmld he rereivinp theanmr nmomt ot hrnr energ" per unit timrj. Suaprnd one thermometer in each beaker and recurd the ttrnperaturr aithe water ineach beaker at l-min intervals for5 min. A comparisonof AT and AT/g for the water in the two beakers illustrates the point. Results can he graphed. Heat of Vaporization Turn the hot plate to a high setting. Take two identical 2M)-ml beakers. Fill one with 100 ml of water (A) and the other with 5.0 ml of water (BI. Put both beakers on the hot d a t e . Record the temoerature of the water in beaker A: (1) . . at the instant the water ~ n r t to c boilin beaker H,and 1 2 , at thernstant that allultheuater has h~iledour ot heaker H. Lsing 1.00 cal g "C tor the sprciiic hear of water. d = 1.00 g ml, and asauming that the same amount ul heat energy has entered hoth beakers, good valuesfor the heat of vaporization (cal/g) can be obtained. An additional experiment that can he included is the use of equal volumes or weights of two different liquids to compare their specific heats. The energy-temperature experiment can also be used effectively as a lecture demonstration ~
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University of Missouri-St. Louis St. Louis, Missouri 63121
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David L. Garin
Volume 50, Number 7, July 1973
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497
