Thermodynamics Research Center / ThermoML | Fluid Phase Equilibria

ABSTRACT

The solubility of alpha-glycine in water with different additives (sodium nitrate, ammonium nitrate, ammonium sulfate, and ammonium chloride) was measured under atmospheric pressure across the temperature range of (293.15 - 343.15) K at intervals of 10.00 K using a dynamic laser method. Solubility was found to increase with increasing temperature and additive level. The experimental data were correlated with the modified Apelblat model, nonrandom two-liquid model (NRTL), and lambda-h model. The R^2 of the fitting regression indicated good applicability of these models to the glycine solubility data in the studied systems (R^2 greater than 0.99). Apparent standard enthalpy, entropy, and Gibbs free energy changes of the solution were calculated based on the van't Hoff equation to elucidate the dissolution mechanism. The results showed that the dissolving process of glycine was endothermic, and the main dissolution driving force contributor was enthalpy in all the additive + water systems studied. By means of enthalpy-entropy compensation analysis, a non linear change in enthalpy of solution versus change in Gibbs energy of solution enthalpy-entropy compensation plot with positive and negative slopes was obtained for the systems studied. The evaluated values of H^E showed that the mixing process of alpha-glycine in all the systems studied was exothermic.