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Unformatted text preview: Estimation of Freezing Point Depression, Boiling Point Elevation, and Vaporization Enthalpies of Electrolyte Solutions Xinlei Ge* ,, and Xidong Wang Department of Physical Chemistry, Uni V ersity of Science and Technology Beijing, 100083, China, Department of Materials Science and Engineering, Royal Institute of Technology, SE 10044, Stockholm, Sweden, and College of Engineering, Peking Uni V ersity, Beijing 100871, China A novel approach is presented in this work for predicting the values of freezing point depression and boiling point elevation for electrolyte solutions at different concentrations on the basis of the Pitzer theories. This method treats the enthalpy change of the solution between the normal freezing point or boiling point and the real ones to be linear temperature dependence. Compared with the literature values, this method performs very well; also, the temperature-dependent parameters of some salts are incorporated to investigate temperature effects of this method. Furthermore, a method based on the Clausius- Clapeyron equation is derived for estimation of the enthalpy of vaporization of very high concentration solutions at different temperatures, and the predicted results are highly positive. Introduction Research on the thermodynamic properties of electrolyte solutions is very attractive because they are very important for many fields in chemical engineering, geochemistry, and so forth. Several colligative properties, such as freezing point depres- sion(FPD), boiling point elevation(BPE), and enthalpies of vaporization are always recognized as the important properties of numerous industrial solutions. The freezing point of a solution always can be lowered by the presence of electrolyte particles, which is called freezing point depression (FPD). Similarly, the boiling point of a solution with a nonvolatile solute is always higher than the boiling point of the pure solvent because of the vapor pressure lowering by the solute. The difference is called boiling point elevation (BPE). The number of the solute particles, namely, its concentration, is the controlling factor of those properties. If the solution is treated as an ideal solution, the FPD or BPE depends only on the solute concentration that can be estimated by a simple linear relationship with the cryoscopic constant for FPD and the ebullioscopic constant for BPE. However, this is only effective in a diluted solution, and thus the accurate method to predict those properties is still essential. Keitaro 1 proposed a detailed description of FPD for dilute concentration. Gary et al. 2 described a new expression for aqueous solutions accurate up to three molal concentrations by considering the solute/solvent interaction. For BPE prediction, an empirical equation was used to correlate the experimental data of BPE....
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- Summer '11