Energy of Activation Submitted by: John P. Idoux, Northeast Louisiana State College, Monroe, Louisiana 71201 Cheelced by: Charlene McAfee, Hiram College, Hiram, Ohio 44234
PREPARATION
Two half-spheres, one about 2 in. in diam. X 1 in. high and the other somewhat smaller. These can be made by cutting the bottom off thick-walled test tubes. Plastic saltshaker tops of the correct shape may be used. DEMONSTRATION -...- ..- ..... ..- .. The students are asked to imagine the half-sphere on it,srounded side as a system of reactant molecules which must, by acquiring a certain energy, pass through a less stable, higher energy configuration (the half-sphere on its edge) on its wav to the ~ r o d u cstate t (the half-snhere on it;flat side). "When the half-sphere is spun: if it returns finally to the reactant state (rounded side), it is pointed out that the system of reactant molecules did
not acquire sufficient energy to surmount the energy barrier and pass over into products. It is then spun again, this time harder, so that it finally comes to rest on its flat side (the uroduct state). I n this case the reactant system has acquired sufficient energy -. to surmount the barrier and pass over into products. By using two half-spheres of different size, the idea that different systems of reactant molecules have different activation energies becomes quite apparent to the student. REMARKS
The overall response to these analogies is quite favorable and recall is improved.
Volume 46, Number 8, August 1969
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A547
