When the Final Reading Is Unknown

Occasionally it is not possible to obtain Aoo — for example, if the reaction is very slow, if secondary reactions occur toward the end of the primary reaction or if the experiment was terminated before the final reading was obtained. Obviously if a reaction has a half-life of one year it may not be practical to wait for the reaction to be complete. 

Several ways have been developed to deal with a reaction for which the Aoo value is not available. The Guggenheim method, for example, uses paired 

Note the use of date and time arithmetic to calculate the elapsed time between readings. The formula in cell B7 is  

Because the absorbance of the product is being monitored, the formula in cell D7 is  

The Solver was used to minimize the value in the target cell (E18, sum of squares of residuals) by varying the values of the changing cells (C19 and C20, Aoo and/cobsd)- 

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