Density and speed of sound of (iodobenzene + n-alkane) liquid mixtures at T = (288.15 to 308.15) K. Application of the Prigogine-Flory-Patterson model

Abstract

(Iodobenzene + n-alkane) liquid mixtures have been studied experimentally, in terms of densities (ρ) and speeds of sound (c), and theoretically, by the application of the Prigogine-Flory-Patterson (PFP) model. The n-alkanes considered are n-heptane, n-decane, n-dodecane, and n-tetradecane. ρ and c measurements have been performed at a pressure p = 0.1 MPa and in the temperature range T = (288.15 to 308.15) K. Excess molar volumes (VmE) and excess isentropic compressibilities (κSE) have been calculated and correlated by Redlich-Kister polynomials. (∂VmE/∂T)p curves at the same (p,T) conditions have been obtained from correlated VmE values. The mixtures are characterized by the following features: (i) VmE increases with the number of carbon atoms of the n-alkane (n), being negative for n = 7, small and S-shaped with positive and negative values for n = 10, and positive for n = 12 and n = 14; (ii) κSE and (∂VmE/∂T)p are negative, increase with n and are very close to zero for n = 14. From these experimental results and the knowledge of the excess molar enthalpies of mixtures containing fluorobenzene, chlorobenzene or bromobenzene with n-alkanes, we have inferred the presence of structural effects, especially important for n = 7 and less relevant for volumetric properties as n increases. The VmE obtained are compared with those of other (halogenated benzene + n-alkane) liquid mixtures existing in the literature, namely systems with fluorobenzene, chlorobenzene, and bromobenzene. From this comparison and the analysis of the isobaric thermal expansion coefficients of the pure compounds, it is inferred that the interactional effects on VmE do not vary appreciably with the length of the n-alkane, so the observed VmE variation is fundamentally determined by the corresponding variation of the contribution from structural effects. Moreover, the application of the PFP model supports this interpretation, providing free volume contributions to VmE that vary parallelly to VmE with the length of the n-alkane, and interactional contributions that rest approximately constant independently of the n-alkane size.