4. Chemical Potential

The chemical potential μ is used as a measure of the general tendency of a substance to transform. Only a few properties are necessary for a complete phenomenological description of this new quantity. They are easy to grasp and can be illustrated by everyday examples. It is possible to derive quantitative scales of μ values (initially at standard conditions) by using these properties, and after choosing a convenient reference level. A first application in chemistry is predicting whether or not reactions are possible by comparing the sum of potentials of the initial and the final states. This is illustrated by numerous experimental examples. The quantitative description can be simplified by defining a “chemical drive” A as the difference of these sums. In this context, a positive value of A means that the reaction proceeds spontaneously in the forward direction. As a last point, a direct and an indirect measuring procedure for the chemical potential are proposed.