Physicochemical Relationships

Physicochemical relationships are such that soHd potassium chloride can be converted to soHd potassium nitrate ia a one-stage operation of the simplest kiad. The conversion takes place ia a stirred reaction system (Fig. 10). The overall separation is analogous to a rectification and stripping operation ia a distillation process. 

So the concept of variables is more powerful than just changing parameters nor do physical chemists merely vary one parameter and see what happens to others. They search for physicochemical relationships between the variables. 

Since graphical displays of physicochemical relationships are convenient to use, much of the data in this paper are represented by e vs. pH diagrams. Redox potential and pH have been chosen as master variables only for convenience this does not mean that e and pH always can be regarded as independent of each other. 

Various laws restrict the values of the process quantities. These laws may represent either fundamental, empirical physicochemical relationships or experimentally identified equations (from statistical modelling or from dimensional analysis particularizations). In contrast to statistical or dimensional analysis based models [1.14], which are used to fix the behaviour of signal transformers, the models of transport phenomena are used to represent generalized phases and elementary phase connections. Here, the model equations reveal all the characterizing attributes given in the description of a structure. They include balance equations, constitutive equations and constraints. 

Of the numerous applications of Free-Wilson and Hansch analyses (the BioByte QSAR Database [76] contains about 9400 data sets on biological applications and another 9000 physicochemical relationships, July 2003) [60,66-68], only a few shall be discussed here to illustrate the most important features and problems. 

Chromatographic theory describes the physicochemical relationships governing separations. Usually, semiempirical models of the chromatographic process that have a relatively simple thermodynamic background and give a bulk picture of the physical or chemical phenomena are involved. Macroscopic models of the chromatographic process cannot mirror the respective separation mechanisms in any other way. Exceptions to this rule, if any exist, are rather negligible. 

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