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Thermodynamics in GeochemistryThe Equilibrium Model$
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Greg M. Anderson and David A. Crerar

Print publication date: 1993

Print ISBN-13: 9780195064643

Published to Oxford Scholarship Online: November 2020

DOI: 10.1093/oso/9780195064643.001.0001

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Aqueous Electrolyte Solutions

Aqueous Electrolyte Solutions

(p.418) 17 Aqueous Electrolyte Solutions
Thermodynamics in Geochemistry

Greg M. Anderson

David A. Crerar

Oxford University Press

Consider a chemical reaction, involving any number of reactants and products and any number of phases, which may be written where Mi represents the chemical formulae of the reaction constituents and Vi represents the stoichiometric coefficients, negative for reactants and positive for products. An example would be where, if MI is SiO2(s), M2 is H2O, and M3 is H4SiO4(ag), and v1 = –I, i/2 = –2, and V3 = 1, the reaction is Now let’s recall (from Chapter 3) what we mean by an equation such as (13.3). If there are no constraints placed on the system containing M1, M2, and M3 other than T and P (or T and V; U and V; S and P; etc.) then M1, M2, and M3 react until they reach an equilibrium state characterized by a minimum in the appropriate energy potential as indicated by expressions like dGT,p = 0. A corollary of this equilibrium relationship, to be fully developed in the next chapter, is that the sums of the chemical potentials of the reactants and products must be equal. In the example, this would be or or in general terms, No notation is necessary for the phases involved because μ must be the same in every phase in the system. However, if more than the minimum two constraints apply to the system, then any equilibrium state achieved will be in our terms a metastable state, (14.25) does not apply, and the difference in chemical potential between products and reactants is not zero. In our example, a solution might be supersaturated with H4SIO4 but prevented from precipitating quartz by a nucleation constraint, so that μ H4SiO4 – μ SiO2 ~ 2 μ H2o > 0.

Keywords:   density model

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