METHODS TO PREDICT THE VAPORIZATION ENTHALPIES AT THE NORMAL BOILING TEMPERATURE OF PURE COMPOUNDS REVISITED

A previous method for predicting the vaporization enthalpies of pure c ompounds at the normal boiling temperature (T-b) based on (T-b) and th e molecular weight (M) as input parameters is re-examined. A remarkabl e improvement is obtained by introducing new rules to evaluate fictiti ous molecular weights for halogens and phosphorus and by recalculating the empirical parameters of the relationship by regressing new and mo re reliable experimental data for Delta H-b. Further, a new family of relationships for Delta H-b is derived which embodies an empirical par ameter, W-p, whose value is related to the polar character of a molecu le. This parameter is, in turn, a function of T-b and M only. A compar ison is made with some well-known literature relationships based on T- b and the critical parameters in their ability to calculate the vapori zation enthalpies of 110 pure compounds representative of polar, non-p olar and strongly associated molecules.