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The Calculator-Based Laboratory (CBL) system is an inexpensive data-collection instrument that feeds tabular and graphical information directly into either a graphing calculator or a computer. The CBL system and a graphing calculator permit hands-on experiences in both classroom and laboratory settings. This work proposes a demonstration to introduce first-order reactions using the CBL system. It then presents the analysis of two consecutive first-order reactions. The values of the rate constants that govern each reaction's rate are determined using the graphing and statistical capabilities of a TI-83 calculator. The rate constant values are used to obtain a regression equation that models the entire process, predicting the behavior of absorbance versus time as the reactions progress.
This technique is useful because it allows instructors to engage students in an in-class activity analyzing data. It permits rigorous discussion of complex kinetics behavior without overemphasizing tedious mathematical manipulations. The example discussed in this article involves two consecutive first-order reactions whose progress is monitored by observing the change in the absorbance intensity of the solution with time. This example is challenging particularly because all the species in solution contribute to the value of the absorbance.
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