Experimental Determination of Curves of Activity and of Free Energy

Abstract

It is possible to construct a reversible electric cell, the electrodes of which are made from pure metal on one hand, and the solution on the other hand; if the solvent is less electropositive than the solute, we select as electrolyte a mixture of molten salts containing positive ions of the solute. The electrical energy liberated is equal and of opposite sign to the change in free energy corresponding to the following reaction:

$$ {\text{pure}}\:{\text{metal}}\,A{\text{ + alloy}} \to {\text{solution}}\,{\text{in}}\,{\text{alloy}}; $$

for one mole of element A:

$$ \mathop {\Delta \bar G}\nolimits_A = \mathop {\bar G}\nolimits_A - \mathop {\bar G}\nolimits_A^0 = - nF\varepsilon , $$

where $\mathop {\bar G}\nolimits_A$ is the partial molar free energy of constituent A, n is the valency of metal A, F is Faraday’s constant, and ε is the electromotive force of the cell so constituted.