Thermodynamically favourable cell reaction

For = 1, a value of °ceii = 0.6 V corresponds to a value of AG° —60kJmol and K lO at 298 K, i.e. this indicates a thermodynamically favourable cell reaction, one that will tend towards completion. 

It appears that the more thermodynamically favoured redox reactions also become kinetically favoured, so that these reactions predominate. This effect has been used to stabilize semiconductor electrodes by establishing a redox couple in the electrolyte with a redox potential more negative than the oxidative decomposition potential (or more positive than the reductive decomposition potential), such that this electrolyte redox reaction occurs preferentially compared to the decomposition reaction, and scavenges the photo-generated minority carriers. However, this stabilization technique can only be used for electrochemical photovoltaic cells, and it is discussed later in further detail. 

The next step is to inspect the thermodynamic data (Table A.5) for the overall reaction and this is done at three temperatures, 298.15 K, 900 K and 1300 K, representing SPFC, MCFC and SOFC, respectively. Only at PqTq does the thermodynamic data favour the electrically driven reformer. Figure A.4 is for the major calculation route at PqTo. The production of hydrogen at both reformer electrodes in the figure is unusual, if the mind has been concentrating on fuel cells. Moreover, v=l. 

Almost all biochemical reactions are catalysed by enzymes, which are found both inside and outside body cells. Enzymes are a special kind of catalyst which are proteins and which are effective in extremely small concentrations. Their mode of action remains imperfectly understood, but they make possible many chemical reactions which would not otherwise occur at the dilutions and comparatively low temperatures at which life cells operate. Many different enzymes are produced by a single variety of plant or animal species moreover, the same enzymes are usually found in many different varieties of life forms. Enzymes are essential for the normal functioning and development of the human body, and failure to produce even one of them may result in a metabolic disorder. Enzymes are generally far more efficient than ordinary catalysts and can increase reaction rates by as much as 10 -10 times or even more. They are not used up in the reaction and do not influence any equilibrium point. Enzymes lower the activation energy of a reaction but cannot make a thermodynamically unfavourable process favourable. Enzyme-catalysed reactions can give yields of nearly 100% without any by-products. 

---