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One of the most common applications of integrated rate laws is to use them, together with experimental data on concentrations, to determine the order of a reaction with respect to some species. In the standard rate laws, students plot ln(c) versus time and 1/c versus time. By seeing which graph produces a straight line, you can determine whether the reaction is first or second order with respect to that substance, as well as the value of the rate constant and the initial concentration. This tends to be confusing for students. The confusion arises mainly from the fact that students are given or measured reactant concentrations as a function of time. They are then askeed to plot something that may seem only peripherally related to what they have been given or measured, and they find this confusing.
There are alternative forms of the integrated rate laws that avoid some of this confusion because they express directly the relationship between concentration and time. The availability of high quality software for performing nonlinear curve fitting on microcomputers allows students to take an alternative approach to data analysis, one that concentrates on functional forms that may be more natural than some of the algebraic machinations necessary to render relationships into linear forms. An example of the application of such an approach to the analysis of kinetic data is presented in this paper. The program used for the analysis is EasyPlot, but other programs are available to do such analysis.
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