Excess molar enthalpies of (iodobenzene, or 1-iodonaphthalene + n-alkane) liquid mixtures at T = 298.15 K and p = 93 kPa

Abstract

Excess molar enthalpies ($H_{\text{m}}^{\text{E}}$) for iodobenzene, or 1-iodonaphthalene + heptane, + decane, + dodecane, or + tetradecane mixtures at 298.15 K and 93 kPa have been measured using a Tian-Calvet micro-calorimeter. The values of $H_{\text{m}}^{\text{E}}$ are positive and indicate that interactions between like molecules are prevalent. In contrast, our previous results on excess molar volumes ($V_{\text{m}}^{\text{E}}$) are negative for the systems C$_6$H$_5$I + heptane, or 1-iodonaphthalene + n-alkane, which reveal the existence of large structural effects in such solutions. This set of measurements has been used to determine isochoric excess molar internal energies ($U_{V\text{m}}^{\text{E}}$). In the range of n-alkanes considered (n is the number of C atoms of the alkane), values of $U_{V\text{m}}^{\text{E}}$ at equimolar composition decrease from n = 7 to n = 10 and then slightly increase for systems with C$_6$H$_5$I, while decrease slowly for mixtures with 1-iodonaphthalene. These trends fit well with the patterns observed for other alkane mixtures containing cyclic molecules. Dispersive interactions are dominant and those between aromatic molecules with a given halogen atom become stronger when the size of this atom increases due to the corresponding increase of molecular polarizability. The mixtures were studied using the DISQUAC and Flory models. The latter was also applied to n-alkane solutions with C$_6$H$_5$F, or 1-methylnaphthalene. Both theories describe accurately the $H_{\text{m}}^{\text{E}}$ data. In terms of the Flory model, this means that the random mixing hypothesis is largely achieved. On the other hand, the theory overestimates the interactional contribution to $V_{\text{m}}^{\text{E}}$, particularly for systems with C$_6$H$_5$X (X = F, I).