Thermodynamics of complexation of aqueous 18-crown-6 with potassium ion: apparent molar volumes and apparent molar heat capacities of aqueous 18-crown-6 and of the (18-crown-6 + potassium chloride) complex at temperatures (278.15 to 393.15) K, at molalities (0.02 to 0.3) mol · kg −1, and at the pressure 0.35 MPa

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We have measured the densities at temperatures T = (278.15 to 363.15) K and heat capacities at T = (278.15 to 393.15) K of aqueous solutions of 18-crown-6 and of (18-crown-6 + KCl) at molalities m = (0.02 to 0.3) mol · kg −1 and at the pressure 0.35 MPa. We have calculated apparent molar volumes V ϕ and apparent molar heat capacities C p, ϕ for 18-crown-6(aq), and we have applied Young’s Rule and have accounted for chemical speciation and relaxation effects to resolve V ϕ and C p, ϕ for the (18-crown-6: K +,Cl −)(aq) complex in the mixture. We have also calculated estimates of the change in volume Δ r V m, the change in heat capacity Δ r C p,m, the change in enthalpy Δ r H m, and the equilibrium quotient log Q for formation of the complex at T = (278.15 to 393.15) K and m = (0 to 0.3) mol · kg −1.