The enthalpy of dilution of some 1-1 and 2-1 electrolytes in aqueous solution

The enthalpies of dilution of aqueous solutions of RbCl, CsCl, NaF, NaBr, NaI, CaCl₂, SrCl₂, BaCl₂, NaHCO₃, and Na₂CO₃ in the molality range 0.1 to 1.0 mol kg^-1 have been determined at 303.15 K with a microcalorimeter. The relative apparent molar enthalpies L_φ of these solutions have been determined with the aid of an extended form of the Debye-Hückel limiting law: L_φ = S_HI ^{1 2}[{1 + (I/m^θ) 1 2}^-1 - σ/3] + BI + CI 3 2, where S_H is the limiting-law slope, σ = "; 3 ( I m^⊖) ^{3 2}';[";1 + ( I m^⊖) ^{1 2}'; - ";1 + ( I m^⊖) ^{1 2}';^-1 - 2 ln";1 + ( I m^⊖) ^{1 2}';], B and C are empirical constants, I is ionic strength, and m^⊖ is a standard molality (1 mol kg^-1). This equation fits the experimental results with a standard deviation of ±2 cal_th mol^-1 for all the salts. The parameters B and C were examined by relating them to properties of the ions that make up the various electrolytes; B was found to be linearly related to the reciprocal of the crystallographic radius and C was found to be directly related to B.