SIGNIFICANT DISCREPANCIES BETWEEN VANT HOFF AND CALORIMETRIC ENTHALPIES .2.

Isothermal calorimetric titration of 18-crown-6 ether with BaCl2 in pu re aqueous solution over the temperature range 7-40 degrees C gives pr ecise 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 t o van't Hoff enthalpies that differ significantly from the observed ca lorimetric enthalpies. This perplexing discrepancy appears at present to be very widely occurring.