Evaluation of several literature equations to predict the vaporization enthalpies at the normal boiling point

Some literature relations proposed by Vetere are re-examined to simplify their analytical form and to improve their performances. Moreover, their results are compared with those of three literature equations by Riedel, Chen and Liu. Four equations include universal parameters, which can be used for any type of compounds and, to be applied, only require the knowledge of the normal boiling temperature Tb, and of the critical constants Tc and Pc. Other six equations are purely empirical, since they are not based on the corresponding state principle: three of them are function of Tb and of the molecular weight M, while the last three equations need M and the polarity parameter Wp. The parameters of the equations that disregard the use of the critical constants are to be optimised separately for three classes of compounds, namely hydrocarbons, polar compounds and alcohols. Moreover, to have a severe test, nearly 290 experimental data of ΔHvb were processed, chosen from the most reliable reported in the fifth edition of the properties of gases and liquids.

► Eleven equations are examined to evaluate their reliability in calculating the DHb at Tb.
► Four of them are based on the Corresponding State Principle.
► They require to be applied the critical constants Tc and Pc.
► Their empirical constants are universal.
► Seven of them are purely empirical.
► They give the best results for 20 alcohols, 112 hydrocarbons and 151 polar compounds.