Center for Hydrothermal Research and the Department of Chemistry, San Diego State University, San Diego, California 92182, USA.
J Phys Chem B. 2009 Aug 27;113(34):11688-95. doi: 10.1021/jp9049236.
Pabalan and Pitzer (Geochim. Cosmochim. Acta 1988, 52, 2393-2404) reported a comprehensive set of thermodynamic properties of aqueous solutions of sodium sulfate without using ion association or hydrolysis. However, there is now ample evidence available indicating that the ion association cannot be ignored at temperatures T>or=373 K. For example, even at the lowest concentration of their studies (m>or=0.05) and at 573.15 K, less than 20% of SO4(2-)(aq) is available as free ions. In the present study, the integral heats of solution of sodium sulfate were measured to very low concentrations (10(-4) m) up to 573.16 K. The data were analyzed correcting for the hydrolysis of SO4(2-)(aq) and the association of Na+(aq) with SO4(2-)(aq) and NaSO4-(aq) in order to obtain the final standard state thermodynamic properties of completely ionized aqueous sodium sulfate, Na2SO4(aq). From these and the available solubility data, the stoichiometric activity coefficients of saturated aqueous solutions of sodium sulfate were calculated up to 573.15 K and compared with literature data. The stoichiometric activity coefficients of aqueous solutions of sodium sulfate, as a function of temperature at all concentrations (0<or=m<or=msat), were also calculated up to 573.15 K.
帕巴兰和皮策（Geochim. Cosmochim. Acta 1988, 52, 2393-2404）报道了一系列关于硫酸钠水溶液的热力学性质，这些性质没有使用离子缔合或水解。然而，现在有充分的证据表明，在温度 T>or=373 K 时，离子缔合是不可忽略的。例如，即使在他们研究的最低浓度（m>or=0.05）和 573.15 K 下，也只有不到 20%的 SO4(2-)(aq)是以游离离子的形式存在。在本研究中，我们将硫酸钠的溶解积分热测量到非常低的浓度（10(-4) m），直至 573.16 K。为了获得完全离解的硫酸钠（Na2SO4(aq)）的最终标准状态热力学性质，我们对数据进行了分析，以校正 SO4(2-)(aq)的水解以及 Na+(aq)与 SO4(2-)(aq)和 NaSO4-(aq)的缔合。从这些数据和现有的溶解度数据中，我们计算了在 573.15 K 下硫酸钠饱和水溶液的化学计量活度系数，并与文献数据进行了比较。此外，我们还计算了在所有浓度（0<or=m<or=msat）下，硫酸钠水溶液的化学计量活度系数随温度的变化，直至 573.15 K。
