Calcite solubility product and dissociation constants of CaHCO3+ and CaCO30 between 5 and 75 °C
The values of the solubility product of calcite and dissociation constants of CaHCO3+ and CaCO30, K3 and K4 respectively, were determined at several temperatures between 5 and 75 °C (calcite becomes unstable at higher temperatures) from measurements [(Ca2+)T, pH] of calcite solubility using carbonically pure water. The results obtained lead to the following empirical expressions for the dependence of equilibrium constants on the temperature : pKs= 7,8156 + 0,03111 T + (1 502/T) - 5,518 log T pK3= 6,2447 + 0,00437 T + (864,479/T) - 0,363 log T pK4= 2,89636 + 0,00707 T + (102,87/T) - 0,44176 log T where log T is the common logarithm of the absolute temperature T(K).Using this expression of pKS, the calculated thermodynamic properties of the calcite dissolution reaction at 25 °C are : ∆H0 = -2510 cal. mol-1, ∆S0 = -47,2 cal. mol-1. K-1 et ∆C∘p = -73,9 cal. mol-1. K-1