Many interesting kinetic equations can only be solved numerically or by introducing approximations, and the latter approach is often the more useful. However, different reasonable approximations (constant concentration of an intermediate or of the substrate) may lead to very different expressions for the integrated rate equation. In this paper, a simple equation for enzyme kinetics is integrated using two approximations, and the results are graphically compared with a numerical solution to the equations. An interactive version of this idea is available on the Cambridge Chemistry Department WWW site: http://www.ch.cam.ac.uk/SGTL/teach/. The use of computers to illustrate the results of the approximations and a comparison with a numerical solution, for different starting conditions and rate constants, should help students to appreciate the effects of the approximations and the regions for which they are valid.
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