Dav M. Shindell, Carl Magagnosc, and Daniel L. Purich Unlverslty of Cal forma Santa Barbara. 93106
I Teaching with an Interactive Reaction I Kinetics Simulator
Simulation techniques constitute an almost inescapable tool for analyzing the kinetics of complex chemical systems ( I ) . Both analog and digital methods have been commonly employed to predict the time dependence of various reaction systems (many of which do not have general mathematical solutions), to validate relationships between models and ohserved svstems, and to estimate the magnitude of rate constants that cannnt he mw~suredd ~ r c c t l i In . addition Lo its truditionnl use in thc lahoratory,simulatirnn methodsare vrrv itttractivr for the teaching c ~ chemical f and enzyme kinetics c,,uries. There, they rnn he used to demonstrate various hasic kinetic princ~ples,illuitrare the use of a m m o n assumptions (such its the stendv state and equilihriunl assumptionsl, and provtde students with a feeling for the mngnitudes 111rate constants in particuli~rsystems. Kinrttc simulnti~mhas evolved cnnsiderahly since early mechantrill diffrnwtial nnalyrers wrre first applied by Chance , 2 ) w e r 30 ) w r s sgu to the simulation of simple rnzyme systems. Ik:lt.ctronic analog computers have sincr heen routinely usrd to model small svntenis, hut the circuitry ol'nn analog computer can quickly become too complicated to program the number of branched pathways or intermediate species increases. Use of high speed digital computers has been a great advance for those interested in kinetics. as it has simnlified the task of programming large schemes (1.3-5). In the simplest form, these packages of computational routines attempt to directly replace the analog computer with digital algorithms, requiring a circuit diagram analogous to the one needed on an analog computer. Programming of a particular scheme is accomplished hy inputting parameters and connections in tabular form. More advanced packages (such as the IBM CSMP and the CDC MIMIC) employ a Fortran-like structure for the inputting of the differential equations describing a articular mechanism. In all the above cases, the user has the iesponsibility to translate the chemical mechanism into a form usable by the computer and to select simulation parameters consistent with the required accuracy. Recently, Edelsen (6) has employed a translator to take pseudochemical notation innut and automaticallv. nreoare . . a data table for a similar integration program. In considerinr! the need for an imoroved simulator with a much s i m l h pr&ncc81for use in the ciassnmm and laboratory, we drfined t hr fcdlowing ;IS essential featurrs: I IJa turtl-key deviw with t h simplrst ~ possible operation, 121useof natural chemical I;rtiau,xy and nutatton, (3) elimination (nf the intermediate steps of -kiting differential equations and translating them into an analog circuit or a digital program, (4) an accuracv much imoroved over the tvoical small analor! -comwter, . (5)provision ;or the user to interact with the simulator and ranidlv (6)automatic selection of . . modifv. innut . narameters. . cimulntion parameters 1 8 , ensure rccurste and rapid simularwni u ith on internal ehtimatim oferror. and (71m d e s t cost (88-10,000) and size (desktop). Together, these features specify an inexpensive unit for student use without requiring any programming or computer knowledge, especially important in teaching introductory or survey courses. The reaction kinetics simulator shown pictorially in Figure 1A meets all the above criteria. This digital simulator, of course, constitutes a compromise hetweenthe performance of electronic analog computers and large digital computers. The simulator is
limited to about 15 uni- or hi-molecular reactions with as many 11s 20 chemical species, pr~vid6.dthe scheme is not particularly stiff. Certainly, this is much less thnn other, more elahorate systems such as the HKI.L(.'HEM compiler 161.Yet. fa,r most phvsirul.organic and general chrmical kinetics work, the number of elementar!." atens . falls a,ithin the ranrtfof - this system. In this report, we describe the teaching applications of a micro computer-based reaction kinetics simulator meeting the above requirements and possessing other convenient features (7). In particular, we illustrate the utility of the simulator in teaching chemical principles by use of selected examples.
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708 /
Journal of Chemical Education
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