Enthalpy, entropy, and temperature of the phase change liquid-gas - An analysis of data of 719 materials regarding systematic correlations

摘要

In this paper, literature data of 719 materials on the enthalpy of evaporation h(v) and boiling temperature T-b, including calculated entropy of evaporation s(v), have been analyzed regarding systematic correlations in phase change liquid-gas. It has been observed that several groups of materials exist that form clusters with an almost linear correlation in an h(v) - s(v)/R graph. One such cluster is formed by the metallic elements. A second cluster is formed by the halogens, the noble gases, and most of the diatomic molecules. A third cluster is formed by the linear alcanes. The knowledge about these clusters can be used to improve rules to predict certain values like in group-contribution methods, and maybe also to identify a common microscopic origin. Additionally, the analysis has shown that many materials have s(v)/R deviating significantly from the Trouton constant. Deviations are more frequent to higher values, and deviations are more pronounced in compounds with few atoms. A chemical reaction upon evaporation has been identified in 12 cases; the formation of larger compounds upon condensation seems to be the main reason for exceptionally high values of s(v)/R. The analysis thus led to a deeper understanding of the physical and chemical origins on the atomic and molecular level.