Geological equilibrium, involving

Effect of Salt Concentration on Geological Equilibrium involving Water... 

Helgeson, H.C., Brown, T.H. and Leeper, R.H., 1969a. Handbook of Theoretical Activity Diagrams Depicting Chemical Equilibrium in Geologic Systems Involving an Aqueous Phase at One Atmosphere and 0—300 C. Freeman and Cooper, San Francisco, Calif., 253 pp. 

In general, the formulation of the problem of vapor-liquid equilibria in these systems is not difficult. One has the mass balances, dissociation equilibria in the solution, the equation of electroneutrality and the expressions for the vapor-liquid equilibrium of each molecular species (equality of activities). The result is a system of non-linear equations which must be solved. The main thermodynamic problem is the relation of the activities of the species to be measurable properties, such as pressure and composition. In order to do this a model is needed and the parameters in the model are usually obtained from experimental data on the mixtures involved. Calculations of this type are well-known in geological systems O) where the vapor-liquid equilibria are usually neglected. 

The above analyses show that it is fairly easy to deal with temperature variation for unidirectional elementary reaction kinetics containing only one reaction rate coefficient. Analyses similar to the above will be encountered often and are very useful. However, if readers get the impression that it is easy to treat temperature variation in kinetics in geology, they would be wrong. Most reactions in geology are complicated, either because they go both directions to approach equilibrium, or because there are two or more paths or steps. Therefore, there are two or more reaction rate coefficients involved. Because the coefficients almost never have the same activation energy, the above method would not simplify the reaction kinetic equations enough to obtain simple analytical solutions. 

Tnorganic geochemistry is dominated by equilibrium processes. Most reactions are rapid, and thermodynamic equilibria are established within geologically short time spans. Many reactions which appear slow in the laboratory still proceed sufficiently fast to influence the composition of geological systems. Noteworthy exceptions involve certain metastable ions like CO32", S042-, and P043-, which may persist even in unfavorable environments for millions if not billions of years. 

When the equilibrium pressure is reached, certain secondary phenomena can still contribute to increase the final volume of the cavity, and above all to significantly increase the weight of rock initially melted by the shock. This mainly involves the melting to a certain thickness of geological material close to the walls under the effect of the temperature of residual hot gases, and the total or partial melting of blocks of rock which become detached from the fractured walls and fall into the hot lava meniscus when the pressure starts to drop. 

A large number of studies have now been reported on the measurement of diffusion coefficients of isotopic species (e g. 0/ 0) in silicates, oxides and carbonates at elevated temperatures and pressures (see Tables 2, 3 and 4 in this study, or Brady 1995). Those of most relevance, geologically, involved the experimental interaction of a mineral (melt, glass) and either pure water, an alkali chloride solution that is in approximate chemical equilibrium with the solid (e.g. albite and NaCl), or a dry gas such as O2 or... 

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