Table of Contents
ISRN Physical Chemistry
Volume 2012, Article ID 521827, 5 pages
Research Article

Determination of Molecular Diameter by PVT

Department of Chemistry, Payame Noor University, P.O. Box 19395-3697 Tehran, Iran

Received 3 December 2011; Accepted 3 January 2012

Academic Editors: S. C. Farantos and T. Panczyk

Copyright © 2012 Vahid Moeini and Mehri Deilam. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.


We derive an equation for calculation of molecular diameter of dense fluids, with using simultaneous Lennard-Jones (12-6) potential function and the internal pressure results. Considering the internal pressure by modeling the average configurational potential energy and then taking its derivative with respect to volume to a minimum point of potential energy has been shown that molecular diameter is function of the resultant of the forces of attraction and the forces of repulsion between the molecules in a fluid. The regularity is tested with experimental data for 10 fluids including Ar, N2, CO, CO2, CH4, C2H6, C3H8, C4H10, C6H6, and C6H5CH3. These problems have led us to try to establish a function for the accurate calculation of the molecular diameter based on the internal pressure theory for different fluids. The relationship appears to hold both compressed liquids and dense supercritical fluids.