Vapor Pressures and Isopiestic Molalities of the Ternary LiNO3+Urea + H2O System at 298.15 K

Isopiestic vapor-pressure measuremenst were made for LiNO3+Urea + H2O from total molality m=0.4 mol kg-1 to m=6.1 mol kg-1 at 298.15 °K. Measurements were made with NaCl(aq) as reference standard for both pure solutions and for the mixed solutions with various molality fractions of LiNO3 ( 0.25, 0.50 and 0.75 ). The experimental results were treated by a modified forms of Pitzer and McKay-Perring methods. Isopiestic procedure is actually a secondary method for studying VLE , wherin the vapor pressure values are evaluated based upon solvent activities. Accordingly the iso-activity rule of Zdanovskii was tested and the result demonstrated slight discrepancy fom semi-ideally behavior. Based on the optimized values of the interaction parameters of modified Pitzer model, osmotic coefficients and activity coefficients of the ternary and of the both limiting binary constituents (LiNO3+H2O) and ( CO(NH2)2+H2O) were calculated and compared well with those evaluated by McKay-Perrig method. Lastly excess energy of Gibbs was evaluated and the interaction of the dissolved components are indicated by the high, negative values [1-4].