Negative pressure of stretched liquid water. Geochemistry of soil capillaries

Solution-mineral equilibria in the unsaturated zone above aquifers requires us to take into account the negative internal pressure of liquid water, di stributed in fine pores of a partially filled medium. The proposed method a ffords calculation of the thermodynamic properties of capillary water by ex trapolating their dependencies measured at positive pressures, into a negat ive pressure domain, finding supports from measurements already obtained on the stretched water. Besides Gibbs free energy, enthalpy, entropy, heat ca pacity, isobaric expansibility and isothermal compressibility of soil water , calculations of the dielectric constant, the water-air interfacial tensio n and the pH at neutrality have been established. This thermodynamic charac terization of the water state in soils enables us to consider quantitativel y the melting and boiling temperatures in soils or in fluid inclusions, the corresponding latent heat, or the lowering of the saturated vapour pressur e in the unsaturated zone of weathering profiles. This pressure approach im plies some reviewed consequences about solute species, gases and mineral so lubilities, or still hydration-dehydration phenomena, in capillaries. Copyr ight (C) 2001 Elsevier Science Ltd.