Significant Discrepancies Between van't Hoff and Calorimetric Enthalpies

In this paper we show that the usual assumption in studies of the temperature variation of equilibrium constants for equilibria of the form A + B$\rightleftarrows$AB that a plot of ln K vs. 1/T (K = equilibrium constant, T = temperature in degrees kelvin) is a straight line with slope equal to -Δ HvH/R (ΔHvH= van't Hoff or apparent enthalpy, R = gas constant) is not valid in many cases. In all the cases considered here, ΔHvHis temperature dependent and is significantly different from the true or calorimetrically measured enthalpy, and the respective values for ΔCpare also significantly different.