edited by: DELORENZO Middle Georgia College RON
Cochran. Georgia 31014
Election Results ana Reactions Yields Romeu C. Rocha-Fllho Universidade Federal de Sao Carlos, 13560 Sao Carlos, SP. Brazil
While chemistry students often have trouble with elementary stoichiometry problems involving a limiting reagent', my first-year students also have problems with the reaction yield concept. Reactions do not always proceed to products as expected from the stoichiometry. Sometimes oniy a fraction of the reagents undergo reaction, while a t other times, side products i r e formed due to competing reactions. Thus, the actual yield of a desired product is often much less than the theoretical yield. My students' understanding of the actual-yield concept has been improved by the use of an election result analogy. Eledlon Result Analogy Initially, an analogy is established between theoretical vield and the electorate. The electorate represents the maximum possible number of ballots that couid be cast, which is analogous to the maximum possible number of molecules of a desired p r o d u c t t h e theoretical yield. Thus, for instance, the data in the table show that the "theoretical yield" of the 1980 and 1984 U. S. presidential elections were 164.5 million and 173.9 million, respectively. Secondlv. an analoev is established between actual vield andvotingturnout. T L , the data in the table show that the "actual yields" of the 1980 and 1984 presidential elections were 86.5 million and 89.3 million, respectively. Students then calculate the 1984 and 1980 election percentage yields as 51.4% and 52.6%, respectively. I t is interesting to mention to the studerr.ts tbat although the 1984 actual vield is ereater than the 1980, the yield is actuall; small&.
' Kalantar, A. H. J. Chem. Educ. 1985, 62, 106.
The extension of the analogy to equilibrium systems was original-
ly suggested by one of the anonymous referees.
248
Journal of Chemical Education
Some Data (all numbers indicate millions) for the 1980 and 1984 US. Presidential Elections Year
Electorate
Turnout
Re~ublicanvote
Democratic vole
1980 1984
164.5 173.9
86.5 89.3
43.9 52.6
35.5 36.5
In addition. through the analoev -" i t can be shown that the reaction-yield concept may be applied to specific desired ~roducts.Thus, as the table shows. in 1980 Reagan's actual bield (the ~ e p u b l i c a nvote) was 43.9 million &d Carter's actual yield (the Democratic vote) was 35.5 million; these translate into the following percentage yields: 26.7% and 21.6%, respectively. In 1984 hoth Reagan's actual yield (the Republican vote) and the percentage yield increased: 52.6 million and 30.2%, respectively; Moudale's (the Democratic vote) were 36.5 million and 21.0%, respectively. These figures do not add up to the respective election yields (due to a number of independent or write-in candidates): thus this information couid also be used to calculate the y'i'eld of "uudesired or unidentified ~roducts".Furthermore. it mav be mentioned that although Mondale's actual yield was bit bigger than Carter's in 1980, his percentage yield was a bit smaller. I have found that the use of this type of analogy helps students tovisualize the reaction yield concept immediately. I t should he mentioned tbat the analogy is only thoroughly applicable to one-to-one stoichiometries. But, on the other hand, this analogy is directly applicable to yields of physical processes, such as recrystallization, distillation, etc., and, also, to equilibrium systems (nonvoters = unreacted starting c~mpounds).~ Finally, it is quite versatile, since it can be used with the most current election results availahle, be i t presidential, gubernatorial, or student council.
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Acknowledgment 'l'hr prwision ofinrormatianab~utU. S. presidentinlelectioni 11). llSlS Reference I.ihrary in SHo Paulo ( B r a d ) and by Mary E. Krilmer, R(.tkrencr Specialist uf the I.ihrary of Cwgrcis (Washington, DCJ,is gratefully acknowledged.
