Standard free energies

A. Gibbs free energy—standard cell voltage... 

Standard free energy Standard free energy of a reaction gives die increase of free energy when the reactants, all in their standard states of unit pressure or unit concentration are converted at constant temperature (7) into the products, which are also in their standard states. The standard free energy is given by the expressions,... 

ESTIMATE OF RELATIVE FREE ENERGIES STANDARD STATES... 

Estimate of Relative Free Energies Standard States 47... 

It is very difficult for a chemical equihbrium not to be altered when passing from gas phase to solution. The free energy standard of reaction, AG , is usually different in the gas phase compared with the solution, because the solute-solvent interactions usually affect the reactants and the products with different results. This provokes a displacement of the equilibrium on passing from the gas phase to the midst of the solution. 

If the buried metal structure involves contact between different metals (such as mild steel, copper, bronze, brass, aluminum, zinc, lead, stainless steel, cast iron, etc.), it is possible that local galvanic cells can form in the contact areas (Figs. 8-9). Each mettd has its own tendency to corrode. An alternative way to express the metal reactivity is to look at the excess of its free energy (standard electrochemical metal potential) and predict the electromotive force emf) between metals in contact, as a general indication for the corrosion process (Table 2). The metal that has a more positive potential is nobler in the galvanic cell, and it is a cathode. The metal with a more negative potential is more active and acts as an anode in the corrosion cell, e.g., it suffers corrosion. 

Gas fraction as a function of distance x Gibbs free energy Standard Gibbs free energy Standard Gibbs free energy of formation of species j... 

Metabolic quotients expressed in microliters me-tabolite/mg dry weight/hour Increment of free energy Standard free energy change Standard free energy change at pH 7... 

Figure 4. Enlargement of the central portion of figure 3, showing the relationship between free energy standard error, entropy of reaction, and temperature standard error.

Figure 5. Effect of free energy standard error (in calories) on temperature standard error for the brucite (+), muscovite (o) and chlorite (A) equilibria. In each case the large square indicates the temperature standard error calculated from the entropy of reaction and the actual standard error of the free energy of reaction. Other points on each curve were calculated by the Monte Carlo Method using arbitrarily assigned errors of the individual minerals.

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