Experimental Methods for Determining Rate Laws

Many different techniques have been used to detect trace intermediates. These include  

Each of these techniques has drawbacks. For example, if a reactant has an emission band in the same region of the spectrum as the intermediate, spectroscopic detection will fail. Other difficulties arise because the speed of the reaction may limit the time available for observation. 

An almost unlimited number of ways have been proposed to monitor reaction. Among the more common are  

It is not always simple to determine the concentrations from the measured property. Consider light absorption in a multicomponent system. The frequency-dependent absorbance A ty v) is related to the concentrations by the Beer-Lambert law 

In all cases the time required for a measurement (the response time of a particular technique) must be short compared with the time during which significant composition changes occur. For example, method 8 is well suited to reactions with half-times on the order of hours but requires great ingenuity when applied to reactions with short half-times. The practical limits of various techniques are summarized in Fig. 4.1. 

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