The thermodynamics of the formation of complexes between diethylenetriaminepenta-acetic acid and the alkaline earth metal ions

Abstract

The enthalpy changes accompanying the formation of complexes between diethylenetriaminepenta-acetic acid and the alkaline earth metal ions, in aqueous solution at an ionic strength of 0·1M, have been measured using an isothermal fusion calorimeter. The results for the complexes of Mg²⁺, Ca²⁺, Sr²⁺, and Ba²⁺ are 2·6, –5·6, –6·7, and –6·9 kcal. mole^–1, respectively. The enthalpies of complexing have been combined with the appropriate free-energy changes to give the entropy changes.