Relation of crystalline forms I, III, IV, and V of anhydrous sodium sulfate as determined by the third law of thermodynamics
Relation of crystalline forms I, III, IV, and V of anhydrous sodium sulfate as determined by the third law of thermodynamics
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热力学第三定律确定的无水硫酸钠晶型I、III、IV、V的关系
DOI：
10.1021/j100649a024
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发表时间：
1972
期刊：
影响因子：
--
通讯作者：
W. Giauque
中科院分区：
文献类型：
--
作者：
G. Brodale;W. Giauque
测量了亚稳态Na 2S 〇 4（III）在15至300 K的热容。这些数据与从稳定的Na 2S 〇 4（V）到Na 2S 〇 4（III）的转变的量热以及在高于300 K的温度下的可用量热数据相结合，与热力学第三定律一起使用，以表明Na 2S 〇 4-（III）在从0至517 K的所有温度下都是亚稳态的，其中它与Na 2S 〇 4（V）平衡，Na 2S 〇 4（V）本身已经变成亚稳态。Na 2S 〇 4（III）先前被认为在高于458 K的温度下是稳定相。发现相Na 2S 〇 4（IV）具有比Na 2-S 〇 4（V）高75 cal/mol的焓含量，并且这被认为是在458 K下从稳定的Na 2S 〇 4（V）到稳定的Na 2S 〇 4（IV）的转变热。Na 2S 〇 4（IV）的稳定性上限取为514 K。这两个温度，458和514 K，是克拉切克和吉布森发现的唯一稳定的转变温度，他们使用了一个装有固体的弹，使其与水溶液接触以获得平衡。热容、熵、焓和自由能函数已被制成Na 2SO 4（V、IV、III和I）的表格。这些数据预测在514 K和熔点之间稳定的形式Na 2SO 4（I）可以在509 K下经历转变，Na 2SO 4（I）到Na 2SO 4（III），其中两相都是亚稳的。克拉切克和吉布森也用干燥的Na 2SO 4记录了这个转变温度，尽管他们把它归因于Na 2SO 4（I）-* Na 2SO 4（II）的转变。在这个实验室里，对硫酸钠体系与热力学第三定律的关系的兴趣始于Pitzer和Coulter 2的发现，即当冷却到极限低温时，十水合物具有剩余熵。在这里研究了许多其他水合物而没有发现这种剩余熵的其他情况之后，似乎有必要检查Na_2SO_4·10 H_2 O的工作。其主要原因是本实验室积累的经验，这些经验与假设对水合晶体中水的总体分析给出了存在的相的真实描述所引起的困难有关。Brodale和Giauque 3重复了对Na 2SO 4·10 H2（）的研究，包括在明确已知相的条件下水溶液的热。他们的实验证实了Pitzer和Coulter的剩余熵结果。2过去和现在都没有理由质疑Pitzer和Coulter对常温下稳定的无水Na 2SO 4形式（V型）的低温热容测量。然而，Brodale和Giauque决定测量无水Na 2S 〇 4的化学不稳定形式（形式III）的热容将是有意义的，其被认为由于缓慢的反应速率而抵抗转变。Na 2S 〇 4（III）和Na 2S 〇 4（V）形式之间的关系似乎提供了有趣的第三定律比较。虽然热容和溶解热的计算已经完成，但试图将结果与当时在更高温度下的可用信息联合收割机结合起来，表明对高温缺乏一些了解
The heat capacity of metastable Na2S04 (III) has been measured from 15 to 300 K. These data, in combina-tion with the calorimetric heat of transition from stable Na2S04 (V) to NaaSChflll), and available calorimetric data at temperatures above 300 K, have been used with the third law of thermodynamics to show that Na2S04-(III) is metastable at all temperatures from 0 to 517 K, where it is in equilibrium with Na2S04 (V), which has itself become metastable. Na2S04 (III) has previously been considered to be a stable phase at temperatures above 458 K. A phase Na2S04 (IV) was found to have an enthalpy content 75 cal/mol above that of Na2-S04 (V) and this has been taken as the heat of transition from stable Na2S04 (V) to stable Na2S04 (IV) at 458 K. The upper limit of stability for Na2S04 (IV) was taken as 514 K. These two temperatures, 458 and 514 K, had been found to be the only stable transition temperatures by Kracek and Gibson, who used a bomb con-taining the solid in contact with aqueous solution to obtain equilibrium. Heat capacity, entropy, enthalpy, and free energy functions have been tabulatedfor Na2S04 (V, IV, III, and I). These datapredict that Na2S04 (I), the form stable between 514 K and the melting point, can undergo a transition, Na2S04 (I) to Na2S04 (III) at 509 K, in which both phases are metastable. Thistransition temperature had also been noted by Kracek and Gibson, using dry Na2S04, although they ascribed it to the transition Na2S04 (I)-* Na2S04 (II).Interest in the relationship of the sodium sulfate sys-tem to the third law of thermodynamics in this labora-tory started with the discovery of Pitzer and Coulter 2 that the decahydrate has residual entropy when cooled to limiting low temperatures. After many other hy-drates had been investigated here without the discovery of other cases of such residual entropyit seemed desir-able to check the work on Na2S04· 10H2O. The prin-cipal reason for this was the accumulated experience in this laboratory relating to the difficulty which can be caused by assuming that the overall analysis for water in a hydrated crystal gives a true account of the phases present. Brodale and Giauque3 repeated the work on Na2S04· 10H2 (), including the heats of aqueous solution under conditions such that the phases were definitely known. Their experiments confirmed the residual en-tropy result of Pitzer and Coulter. 2 There was and is no reason to question the low temperature heat capacity measurements of Pitzer and Coulter on the form of an-hydrous Na2S04 (Form V) stable at ordinary temperatures. However, Brodale and Giauque decided that it would be of interest to measure the heat capacity of a thermodynamically unstable form of anhydrous Na2S04 (Form III) which was believed to resist transition due to slow reaction rate. The relationship between the Na2S04 (III) and Na2S04 (V) forms appeared to offer an interesting third law comparison. Although the heat capacities and heats of solution were completed, attempts to combine the results with the then available information at higher temperatures indicated some lack of understanding with respect tothe high temperature