SIGNIFICANT DISCREPANCIES BETWEEN VANT 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 reversible arrow AB that a plot of In K vs. 1/T (K = equilibrium constant, T = temperature in degrees kelvin) is a straight line with slope equal to -Delta H-vH/R (Delta H-vH = van't Hoff or apparent enthalpy, R = gas constant) is not valid in many cases, In all the cases considered here, Delta H-vH is temperature dependent and is significantly different from the true or calorimetrically measured enthalpy, and the respective values for Delta C-p are also significantly different.