A typical problem in graphical analysis

Problem 7.6 illustrates a procedural problem often encountered by students. 

A plot of loge(fc/7) versus 1 /7 should have slope = —AH /R. 

When the plot of oge(k/T) versus 1/7 is drawn, there is a very long extrapolation to zero for 1/7. To carry out this extrapolation would require a ridiculous amount of graph paper, or a ridiculous bunching together of points on ordinary graph paper. Graphical extrapolation is impossible, and the value of the intercept must be found by calculation. This can happen in various aspects of physical chemistry, and very often occurs in plots vs 1/7. 

As in the gas phase, if the reaction step is bimolecular with two species forming an activated complex resembling a single species, there will be a decrease in entropy on activation. In solution this is called an associative reaction. If reaction is unimolecular and the activated complex resembles an incipient two (or more) species, then an increase in entropy would result. This is termed a dissociative reaction for solution reactions. A reaction somewhere in between these two extremes is termed interchange, and the entropy change is likely to be small. 

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