The absolute chemical hardness η for a chemical system under a steady external potential υ containing N electrons and an energy E(N) was defined by Robert Parr and Ralph Pearson as η = (δ²E/δN²)_υ. Chemical hardness is a widely accepted concept in chemistry that serves as a reactivity index for describing the stability of compounds and reaction mechanisms in the framework of hard and soft acid and base theory. In a previous study, we demonstrated that it is possible to formulate a total energy functional of electronic density that is directly correlated to the experimental data obtained from mesoscopic electrochemical systems. The present study extends the use of this experimentally designed functional to determine and analyze the chemical hardness of mesoscopic electrochemical systems directly from the experimental data. We demonstrate that it is possible to rapidly scan the physical properties and chemical reactivity indexes of mesoscopic electrochemical systems at different external potentials and a finite temperature using the grand canonical ensemble.