Free energy change of reaction

Having calculated the standai d values AyW and S" foi the participants in a chemical reaction, the obvious next step is to calculate the standard Gibbs free energy change of reaction A G and the equilibrium constant from... 

M Tachiya. Relation between the electron-transfer rate and the free energy change of reaction. J Phys Chem 93 7050-7052, 1989. 

Here, Ais the free energy change of Reaction 17.3 (kJ mol 1), R is the gas constant (8.3143 J K-1 mol-1), and 7k is absolute temperature (K). Factor co is the reciprocal of the average stoichiometric number, which can be taken as the number of times the rate determining step in Reaction 17.3 occurs per turnover of the reaction (Jin and Bethke, 2005). 

Fig. 22.7. Thermodynamic driving forces for various anaerobic (top) and aerobic (bottom) microbial metabolisms during mixing of a subsea hydrothermal fluid with seawater, as a function of temperature. Since the driving force is the negative free energy change of reaction, metabolisms with positive drives are favored thermodynamically those with negative drives cannot proceed. The drive for sulfide oxidation is the mirror image of that for hydrogentrophic sulfate reduction, since in the calculation 02(aq) and H2(aq) are in equilibrium.

The free energy change of reaction at the states of interest is then... 

The difference in the free energy changes of reactions (8) and (9) can be expressed as follows... 

AG° is the standard Gibbs free energy change of reaction obtained from the standard energy of formation of pure components AG at 25 °C, P = 1 atm and a suitable aggregation state. Once having determined IQq in standard conditions, the van t Hoff equation may be used to calculate fQq at other temperatures, as follows ... 

STANDARD GIBBS FREE-ENERGY CHANGE OF REACTION 4.5... 

Electron-Transfer Rate and the Free Energy Change of Reaction. 

The electrical work done by Cell I under standard and reversible conditions is a measure of the standard free energy change of Reaction 13. Thus... 

Figure 3. A complete ystematization of modem thermodynamics. Note (AG )t.p, (AG2)t.p and (AG)t.p are Gibbs free energy changes of reaction 1, reaction 2 and the whole system at constant temperature and pressure, respectively. X and J represent thermodynamic force and thermodynamic flux for irreversible process, respectively.

In this case, however, the ISi jO component is at infinite dilution in a host of essentially pure YSi cO. Now we assume that Goldschmidt s first rule applies, i.e., we assume that if I and Y " " had exactly the same ionic radius then the standard free energy changes of reactions (1) and (4) would be the same. The actual difference between the standard free energy changes is assumed to be due to the work done in straining crystal and melt by introducing a cation which is not the same size as the site. This is a reasonable assumption for closed-shell ions such as Ca, Sr, and Mg " " and it also appears to work in those cases, such as the lanthanides, where crystal field effects are small (Blundy and Wood, 1994). For first row transition ions such as Co, and Cu, however,... 

Given the assumption that strain energy is the sole additional contribution when I is introduced, the standard free energy change of reaction... 

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