The enthalpy of dilution and thermodynamics of Na2CO3(aq) and NaHCO3(aq) from T=298 K to T=523.15 K and pressure of 40 MPa

Molar enthalpies of dilution Delta H-dil(m) of Na2CO3(aq) were measured fro m molality m = 1.45 mol . kg(-1) to m = 0.008 mol . kg(-1) at seven tempera tures from T = 298 K to T = 523 K at the pressure p = 7 MPa, and at four te mperatures from T = 371 K to T = 523 K at the pressure p = 40 MPa. Molar en thalpies of dilution Delta H-dil(m) Of NaHCO3(aq) were measured from m = 0. 98 mol . kg(-1) to m = 0.007 mol . kg(-1) at the same temperatures and pres sures. Hydrolysis and ionization equilibria contribute substantially to the measured enthalpies under many of the conditions of this study. Explicit c onsideration of these reactions, using thermodynamic quantities from previo us studies, facilitates a quantitative representation of apparent molar ent halpies, activity coefficients, and osmotic coefficients with the Pitzer io n-interaction treatment over the ranges of temperature, pressure, and molal ity of the experiments. (C) 2001 Academic Press.