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 H2false(normalgfalse) , H+(aq), and e− (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 H2false(normalgfalse)→2H+false(normalaqfalse)+2e− (Pt electrode) is presented. The Galvani potential differences for half cells are calculated, and tables of normalΔG , normalΔS , and normalΔH 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 normalΔG for half‐cell reactions is illustrated by Poyinting's vector.

In this work, an experimental design methodology was applied to optimize the degradation of an Orange II (OII) solution, a non-biodegradable azo dye, while minimizing also the leaching of iron from the catalyst support in a heterogeneous Fenton-like process. The independent variables considered were the temperature, H2O2 concentration, and catalyst (iron-impregnated pillared saponite clay) load. The multivariate experimental design allowed the development of empiric quadratic models for dye degradation, TOC removal, and iron leaching after 1, 2, 3, and 4 h of reaction, which were adequate to predict responses in all of the range of experimental conditions used. Data obtained revealed that the heterogeneous Fenton-like process is promising for the degradation of the studied azo dye. Actually, after 4 h oxidation color removals near 100% and TOC reductions of at least 65% were experimentally achieved when the temperature was 40 °C or higher. Iron leaching was also quite small after 4 h of oxidation (in the range 0.66−5%), pointing to a good stability of the catalyst. Besides, the optimal conditions depend on the response factor considered, being advisable to use less-aggressive conditions if responses are taken at longer reaction times. Particularly, temperature, but also catalyst concentration, were found out to be the main parameters affecting all of the responses (dye degradation, TOC removal, and iron leaching), whereas the effect of the initial H2O2 concentration was found to be negligible. Finally, the process was optimized considering the three responses simultaneously, allowing defining optimal regions for the significant process variables (temperature and catalyst dose in the slurry batch reactor).

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