Thermodynamics of solution of cyclic alkanes from C 5 through C 11 in n-C 36H 74 at 373.15 K using gas-liquid chromatography

Abstract

Enthalpies and entropies of solution from the 1 atm vapor state to the infinitely dilute solution in n-C 36H 74 at 373.15 K have been measured for cyclic alkane solutes containing 5 through 11 carbon atoms. Enthalpies of solution are more negative than those exhibited by corresponding normal alkanes by about 0.5 kcal th mol −1. The difference is attributed to the considerably smaller molar volumes of the cyclic alkanes, requiring less energy input upon solution. While the entropies of solution of n-pentane and cyclopentane are very nearly the same, the cyclic alkanes display increasingly less negative values relative to the n-alkanes as the number of carbon atoms in the solute is increased, resulting in much lower equilibrium partial pressures for the cyclic molecules. The observed entropies of solution are predicted by a simple equation based on volume fraction. It appears that for normal and cyclic alkanes, molar volume is the most important variable in determining solution properties at infinite dilution.