Thermodynamic relations and equilibria in (Na2CO3 + NaHCO3 + H2O): standard Gibbs energies of formation and other properties of sodium hydrogen carbonate, sodium carbonate heptahydrate, sodium carbonate decahydrate, trona: (Na2CO3*NaHCO3*2H2O), and Wegscheider's salt: (Na2CO3*3NaHCO3)

Article abstract of DOI:10.1016/0021-9614(82)90013-1

Literature results for numerous heterogeneous equilibria in the three-component system (Na2CO3+NaHCO3+H2O) or (Na2CO3+CO2+H2O) were critically evaluated.Careful attention was given to evaluation of activity coefficients and pressure effects.Temperature effects were treated using enthalpies of formation determined previously for the reacting species.Standard Gibbs energies of formation at 298.15 K were evaluated: -(2714.94 +/- 0.30) kJ/mol for Na2CO3*7H2O(s); -(3428.61 +/- 0.40) kJ/mol for Na2CO3*10H2O(s); -(851.30 +/- 0.19) kJ/mol for NaHCO3(s); -(2381.33 +/- 0.55) kJ/mol for trona: Na2CO3*NaHCO3*2H2O(s); -(3604.72 +/- 0.80) kJ/mol for Wegscheider's salt: Na2CO3*3NaHCO3(s).Corresponding standard entropies at 298.15 K are: (422.36 +/- 1.50), (562.74 +/- 1.15), (102.36 +/- 0.80), (303.13 +/- 1.70), and (433.33 +/- 2.50) J/K*mol, respectively, in the same order.The upper temperature limit for existence of trona was evaluated as 395 K.NaHCO3(s) heated in a small closed container forms a saturated solution of NaHCO3(s) and Na2CO3*3NaHCO3(s) at 402 K and above.Likewise, Na2CO3*3NaHCO3(s) heated in a small closed container forms a saturated solution of Na2CO3(s) and Na2CO3*3NaHCO3(s) at 460 K and above.The results permit interpretation of equilibria in the system up to at least 600 K.