Thermodynamics of complexation of aqueous 18-crown-6 with rubidium and cesium ions: Apparent molar volumes and apparent molar heat capacities of aqueous (18-crown-6 + rubidium chloride) and (18-crown-6 + cesium chloride) at temperatures (278.15 to 393.15)

We have measured the densities at temperatures T = (278.15 to 368.15) K and heat capacities at T = (278.15 to 393.15) K of aqueous (18-crown-6 + RbCl) and (18-crown-6 + CsCl) at m = (0.02 to 0.33) mol · kg−1 and at the pressure 0.35 MPa. We have applied Young’s Rule and have accounted for chemical speciation and relaxation effects to resolve Vϕ and Cp,ϕ for (18-crown-6–Rb+,Cl−)(aq) and (18-crown-6–Cs+,Cl−)(aq) in the mixtures. We have also calculated values of the change in volume ΔrVm, the change in heat capacity ΔrCp,m, the change in enthalpy ΔrHm, the equilibrium quotient lg Q, and the change in entropy ΔrSm for formation of the complexes at T = (278.15 to 393.15) K and m = (0 to 0.33) mol · kg−1. These results are compared with those recently obtained for the aqueous complexes of 18-crown-6 with K+, Na+, and Ba2+.