7.4.1 Graphical Differentiation Method

This method is very old (from slide rule days—“What’s a slide rule, Grandfather?”), when compared with the numerous software packages. So why do we use it? Because with this method, disparities in the data are easily seen. Consequently, it is advantageous to use this technique to analyze the data before planning the next set of experiments. As explained in Appendix A.2, the graphical method involves plotting (–ΔC_A/Δt) as a function of t and then using equal-area differentiation to obtain (–dC_A/dt). An illustrative example is also given in Appendix A.2.

In addition to the graphical technique used to differentiate the data, two other methods are commonly used: differentiation formulas and polynomial fitting.