Thermodynamics of complexation of aqueous 18-crown-6 with sodium ion: Apparent molar volumes and apparent molar heat capacities of aqueous (18-crown-6 + sodium chloride) at temperatures (278.15 to 393.15) K, at molalities (0.02 to 0.30) mol . kg-1, and at the pressure 0.35 MPa

We have measured the densities at T = (278.15 to 368.15) K and heat capacities at T = (278.15 to 393.15) K of aqueous solutions of (18-crown-6 + NaCl) at molalities m = (0.02 to 0.30) mol . kg-1 and at the pressure 0.35 MPa. We have also measured densities and heat capacities of mixtures containing excess 18-crown-6 and excess NaCl. We have applied Young's rule and have accounted for chemical speciation and relaxation effects to resolve V φ and C p,φ for (18-crown-6-Na+,Cl-)(aq) in the mixture. We have also calculated values of the change in volume Δr V m, the change in heat capacity Δr C p,m, the change in enthalpy Δr H m, and the equilibrium quotient log Q for formation of the aqueous (18-crown-6-Na+) complex at T = (278.15 to 393.15) K and m = (0 to 0.30) mol . kg-1. These results are compared with those recently obtained for the complexes of 18-crown-6 with Ba2+ and K+