Significant discrepancies between van't hoff and calorimetric enthalpies. II

Isothermal calorimetric titration of 18‐crown‐6 ether with BaCl₂ in pure aqueous solution over the temperature range 7‐40 °C gives precise binding constants and enthalpy changes. Nonlinear least‐squares fitting of the binding constants to the integrated van't Hoff equation, including a temperature‐independent change in heat capacity, leads to van't Hoff enthalpies that differ significantly from the observed calorimetric enthalpies. This perplexing discrepancy appears at present to be very widely occurring.