Chemical potential: is it there?

I wrote this title because rarely we hear or use the value of chemical potential for chemistry purposes. This became a hot topic (one of the most discussed) in the 2007 IUPAC congress in Torino. Chemical potential is believed as a part of physical and thermodynamical chemistry but less favorable than other terms, such as: entropy, enthalpy. Even, most of students probably never hear the use of this value to calculate their thermodynamic problem. It is more to the ‘ego’ of chemists to describe their ‘own world’ (just an opinion).

Taken from the general description, chemical potential is used to measure the tendency of a substance to change. To change means could be reaction, evaporation, condensation, and so on. The idea is by comparing the potential of the initial and the final state of their sum potential, the possible change (e.g. reaction) can be predicted. This can be done by choosing the appropriate reference point. So, the use of chemical potential is such kind of ‘chemical drive’ for the change of the things.

Here the example, a candle burns  because the initial substance combined (take an example of atmospheric oxygen and paraffin, say CH₂) have higher chemical potential than the product (could be CO₂ and water vapor): 3 u_(O2) + 2 u_(CH2) > 2 u_(CO2) + 2 u_(H2O). You can say, it is easy to solve by using the value of Gibbs energy different between product and reactant. Lower Gibbs energy of product means that it is very possible. In the case of chemical potential, the values of the chemical potential of substance are related to the chemical potentials of the elements they are composed of and can be determined experimentally by use of chemical reactions. Because it is not possible to transform one element into another by chemical means, the values of the various elements themselves are not related to each other. For simplicity, the zero (0) value is taken for all element value.

So, the chemical potential u of an arbitrary substance itself depends upon temperature and pressure (and possibly other parameters), u(T,p,..) and remember, it is based on the substance (referred to the element) that form them. Using this description, we can have different value of chemical potential depends on the base of element and process that we can have.

Almost every cases can be calculated using this term for example, solubility, temperature gradient, concentration which, again, the value will be depend on the basis element and case.

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