Analysis of Free Energy and Entropy Changes for Half‐Cell Reactions

A comprehensive study of different entropy scales used in chemical thermodynamics is presented, and a semi‐absolute entropy scale is introduced, by which problems involving noncharged and charge species can be considered correctly and further, the heat generation of half‐cell reactions can be calculated. In this context, the entropy of an electron in a metal is derived. The entropy changes for electrode reactions are calculated, and the heat distribution among the electrodes of the cell is solved. The correlation of the zeros of the energy scales for , H+(aq), and (vacuum) is studied, and the value of chemical potential of electron in metal and gas phase is derived. An estimation for the free‐enthalpy change for the half‐cell reaction (Pt electrode) is presented. The Galvani potential differences for half cells are calculated, and tables of , , and are presented. An example of the use of half‐cell reaction entropies and free‐energy changes for a fuel cell is presented. With this method we can establish how the total heat generated in the fuel cell is distributed between the cathode and the anode of the cell. This method gives new basic information on electrochemical cells, which can be applied to mathematical models of single electrodes. The physical meaning of for half‐cell reactions is illustrated by Poyinting's vector.