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)