Pressure Effects on the Equilibrium Constant

In recent years, researchers have attempted to use molal volume and compressibility data to estimate the effect of pressure on ionic equilibria or nonideal solubility. The method of using V and k data to estimate the effect of pressure on ionic equilibria or the solubility of salts was first demonstrated by Owen and 

T) - equilibrium constant at specified pressure and temperature K(T) - equilibrium constant at specified temperature and standard state 

AV - the algebraic difference between the partial molal volumes of the products and reactants in their standard state taking into account the stoichiometry of the reaction (cm /mole) 

Over the years many things have been said about this equation because of the difficulty in getting data. The most common simplification is to avoid the molal compressibility term since k° for a mineral is small and remains relatively constant with temperature. Also the molal compressibilities of ions are hard to find published in the literature and are limited primarily to a range of 0 - 50° Celsius. At lower pressures ignoring this term is probably suitable, but for high pressure the term becomes more important. 

In 1968 Lown, Thirsk and Wynne-Jones (4) have shown that the effect of pressure on ionic or nonideal equilibrium to pressures below 1000 bars can be estimated by K(P,T) = K(T) exp ((-AV P +. 5 Ak P )/(Rr)) (3.41) 

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