| The corrosive nature of Hydrogen fluoride (HF) and its complex interactions with water have limited the development of experimental studies as well as robust thermodynamic models for this binary mixture (HF + H2O). Earlier studies have failed to provide a reasonable description of this binary mixture because of the complex association interactions between these compounds, which were not adequately modeled. In this work, the phase behavior of this mixture is understood by exploring these complex association interactions.; Pure HF was modeled using 14 different association schemes that allow the formations of different physically meaningful oligomers with different distribution schemes (1-2, 1-6, 1-2-6 etc.), where the 1-2 scheme allows the formation of monomers and dimers and likewise. The parameters for these pure component schemes that were obtained by correlating the phase co-existence properties of pure HF were used to predict several other pure component properties. The dominance of these association patterns and their distribution were understood based on their predictive ability. Additionally, as a demonstration of the effect of association in HF, a potential anomaly on the isothermal compressibility (KT) of HF was also reported. Similar to the experimentally supported heat capacity peak, which is understood based on vapor phase clustering in HF, KT was also related to the derivatives of enthalpy and entropy of the system.; In order to identify the cross-association patterns that are likely to be found in the solution, the distribution of association patterns in (HF) m(H2O)n clusters were investigated using cluster studies. This study was performed at the mPW1B95/6-31+G(d,p) level of theory. A total of 214 optimized geometries of (HF) m(H2O)n clusters, with m + n as high as 8, were investigated. The strongest H-bond interaction was reported to be the H2O···H--F interaction. It was also found that the larger (HF)m(H 2O)n clusters and the clusters with equimolar contributions of HF and H2O were preferred in the solution phase.; The pure component association schemes that were developed for HF were extended to the binary mixture with water. The phase co-existence properties were correlated using different association patterns for the pure components with and without considerations for the strong association between them. The significance of these self and cross-association patterns are studied and understood based on the correlative and the predictive ability of the association schemes. |
