A modified Redlich-Kwong equation of state for H (sub 2) -H (sub 2) O fluid mixtures at high pressures and at temperatures above 400 degrees C

Redox equilibria relevant to the Earth's crust and mantle may be viewed as reactions between solids and a fluid mixture of H (sub 2) and H (sub 2) O. Modified Redlich-Kwong equations of state for H (sub 2) , H (sub 2) O and H (sub 2) -H (sub 2) O mixtures are capable of generating reliable fugacity and activity data at T > 400 degrees C, though pure component fugacities may also be computed with considerable accuracy at lower T. The activity coefficients returned by the modified Redlich-Kwong equations are compatible with the constraints of the Gibbs-Duhem equation. A significant positive deviation from ideality is encountered to T <= 800 degrees C, this should be taken into account in computing redox equilibria. A computer program generating f and a for H (sub 2) and H (sub 2) O at desired T, P and XH (sub 2) is available.