Chemistry Everyday for Everyone Applications and Analogies
Audience-Appropriate Analogies: Collision Theory Kent W. Piepgrass Department of Chemistry, Miami University–Middletown, Middletown, OH 45042
Sales Analogy
Analogies provide students with a means of understanding and remembering “target” concepts. For analogies to be effective, the student must be familiar with and able to relate to them (1). Many of my favorite analogies have become ineffective owing to changing lifestyles and demographics. With the diversity now found in most student populations, no one analogy can be expected to be effective, so the wise instructor chooses analogies that are appropriate to the audience. I therefore offer two new analogies for collision theory (2–4 ). Collision theory is based on the assumption that two molecules must collide in order to react. The more collisions, the faster the rate of the reaction. But not every collision is effective. Not only must molecules collide, they must do so with the proper orientation and with sufficient energy to break a bond so a new bond may be formed. We call these three requirements frequency of collision, orientation, and the energy factor ( 5).
For students who are unfamiliar with arcade games, collision theory may be explained in terms of the number of sales transactions in a department store (Table 1). The manager might consider three factors that determine the number of sales. The more customers who are met and assisted by sales clerks, the more sales that will be made. The contact must take place in the right section of the store—the shoe department won’t be able to satisfy a customer looking for kitchen equipment. The price must be acceptable to the customer. This analogy is versatile and is appropriate for discussing the effect of concentration (number of sales clerks and customers relative to the size of the store), activation energy (cost), energy distributions (the relative numbers of affluent and nonaffluent customers). I also introduce the idea of coupons and how they might serve as analogues to catalysts.
Arcade Game Analogy
Limitations
There are many video, computer, and arcade games based upon the martial arts. Most students are familiar with these games. I tell my students that the factors controlling the rate of a reaction may be compared to the scoring in a martial arts arcade game (Table 1). The contestant must accomplish three things in order to win. The contestant must strike the opponent; the more times the opponent is struck the more points are scored. The opponent must be struck in the body or head—arms, shields, etc. won’t count. Finally, the strikes must be delivered with sufficient force or the blow won’t score.
Analogies have their limitations and it is important to realize that students may develop misconceptions from analogies (1, 6 ). If the students have correctly understood the target concepts and analogies they should be able to identify the limitations of the analogies (6 ). I accomplish this by suggesting the analogies mentioned above and having the students identify the similarities as well as the differences. This is usually a straightforward and enjoyable activity.
Table 1. Mapping of Target Concepts and Analogues Target Concept
Arcade Games
Number of collisions Number of blows
Sales Number of contacts
Orientation
Location of the blow Location of the contact
Energy of collision
Force of the blow
724
Item cost vs customer cash
Literature Cited 1. 2. 3. 4. 5.
Duit, R. Sci. Educ. 1991, 75, 649. Nash, J. J.; Smith, P. E. J. Chem. Educ. 1995, 72, 806. Krug, L. A. J. Chem. Educ. 1987, 64, 1000. Last, A. M. J. Chem. Educ. 1983, 60, 748. Brady, J. E; Holum, J. R. Chemistry: The Study of Matter and Its Changes, 2nd ed.; Wiley: New York, 1996; p 604. 6. Webb, M. J. School Sci. Math. 1985, 85, 645.
Journal of Chemical Education • Vol. 75 No. 6 June 1998 • JChemEd.chem.wisc.edu
