Free energy from carbon oxidation

Chemotrophs derive free energy from the oxidation of fuel molecules, such as glucose and fatty acids. Which compound, glucose or a saturated fatty acid containing 18 carbons, would yield more free energy per carbon atom when subjected to oxidation in the cell See Figure 14.10 on page 381 for a comparison. 

The group of microorganisms known as autotrophic bacteria obtain energy from the oxidation of a variety of inorganic compounds (ammonia, nitrite, sulfide, ferrous iron, hydrogen, carbon monoxide, sulfur, thiosulfate).The free energy changes and over-all efficiencies of a number of these processes have been calculated. We may take as an example the oxidation of nitrite to nitrate performed by Nitrobacter... 

As described above, it is obvious from the free energy data that oxides and oxysulfides would be formed first when rare earths are added to molten iron, and sulfur removal is effective only when the oxygen content and its activity are low. Use of a heavy basic slag and 0.2% mischmetal (residual Ce in steel 0.002-0.015%) reduced the sulfur content in one case from 0.012% to <0.001% in plain carbon steels and C 0.003% in 12-13% Cr stainless steels (Grevillius et al. 1971). A 0.5% mischmetal addition resulted in 94% sulfur removal in another case (Bernard 1967). Similar results have been obtained by Dahl et al. (1973). 

Figure Bl.25.2 shows the XPS spectra of two organoplatinum complexes which contain different amounts of chlorine. The spectrum shows the peaks of all elements expected from the compounds, the Pt 4f and 4d doublets (the 4f doublet is iimesolved due to the low energy resolution employed for broad energy range scans). Cl 2p and Cl 2s, N Is and C Is. Flowever, the C Is caimot be taken as characteristic for the complex only. All surfaces that have not been cleaned by sputtermg or oxidation in the XPS spectrometer contain carbon. The reason is that adsorbed hydrocarbons from the atmosphere give the optimum lowering of the surface free energy and hence, all surfaces are covered by hydrocarbon fragments [9].

In this, to the free energy change for the reaction involving the interaction of chlorine and the metal oxide, is added the large value of the free energy of formation of carbon dioxide from its constituent elements. 

The formation of carbon monoxide aids chlorination in exactly the same way as does the formation of carbon dioxide which of the two oxides of carbon would found in the reaction depends on the temperature at which reduction-chlorination is carried out. Below 600 °C carbon dioxide forms while above 700 °C carbon monoxide is formed. This changeover results from the variation in the free energies of formation of these two oxides with temperature. For example, at 900 °C the situation as regards the formation of titanium tetrachloride from titanium dioxide is guided by the reactions ... 

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