Direct Measurement of Chemical Drive

The usual methods do not measure the chemical potentials of substances themselves, but only the difference between the sums of the potentials of the initial substances and the final products, i.e., the drives A / initial X) / final 

Data in a SI coherent unit are desirable. G (Gibbs) is an example which has already been presented here. There is a trick that can be used so that preliminary values do not have to be remembered. We do not assign a value of 1 to the drive Ai of the process which has been chosen as the unit of the chemical drive. Rather, we take a value which comes as close as possible to the value in Gibbs. For instance, 

The cell in Fig. 4.5 represents a fixed value of chemical drive just as the original meter and the original kilogram in Paris represent fixed length and mass values. This example shows the solidification of supercooled heavy water (freezing point 276.97 K), 

As we have already seen in the example of weight (Sect. 1.3), there are basically three agreements necessary for metricization. These are agreements about 

Now we need only think about creating sums (point b). Two or more transformations with the drives A,A, A . .. are coupled to each other— it does not matter how—so that they have to take place together. We make the agreement that the drive Atotsi of the entire process, i.e., of the sequence of the coupled processes, is the sum of the drives of these processes  

---