edited by WALTERA. WOLF Eisenhower College Falls. NY 13148
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An lll~Strati0nof Applied Calorimetry-Dieting Students Robert R. Perkins Memorial University Sir Wilfred Grenfell College Corner Brook. Newfoundland Canada A2H 6P9
As most instructors of introductory chemistry know, questions which both catch the interest of students as well as euemnlifv . . theoretical conceots are difficult to come UD with. I have used the following example with great success in my first-year classes. In any class, a t least one third of the students will be interested in losing some excess weight (mass). I generally describe the concept of calorimetry and discuss the energy involved with changes of phase. This concept is then extended to the possihility of burning off body fat by eating ice cubes instead of strenuous exercise. In addition to illustrating the enthalpy of phase transitions, the question also involves practice with the conversion of units. Let us say that a student wishes to lose 10.0 pounds. Now when 1.110 p of body fat is metabolized, 38.0 kJ of energy is released.' If this energy is used to melt icecubes and warm up the resulting water to hody temperature, loss of hody fat should result. I now ask my students to determine the number of 50.0 g ice cubes a t -20.0°C which would have to be consumed in order to burn off 10.0 lh of fat.
:38'0 kd x 10.0 lb Q v e k d= -
454 g x-
Ib Q,,,,,,., Now if the specific heat of ice and water are 2.09 J .g-' .I
