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 + Ba(NO3)(2)} at molalities m = (0.02 to 0.33) mol center dot 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 V-phi and C-p,C-phi to include contributions of the 18-crown-6-Ba2+(aq) complex in the mixture. We have also calculated estimates of the change in volume A,. V, the change in heat capacity Delta(r)C(p,m), the change in enthalpy Delta(r)H(m), and the equilibrium quotient 1g Q for formation of the complex at T = (278.15 to 393.15) K and m = (0 to 0.33) mol center dot kg(-1) in the mixture. (c) 2005 Elsevier Ltd. All rights reserved.