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翻訳と辞書　辞書検索 [ 開発暫定版 ] スポンサード リンク Van Laar equation ： ウィキペディア英語版 Van Laar equation The Van Laar equation is an activity model, which was developed by Johannes van Laar in 1910-1913, to describe phase equilibria of liquid mixtures. The equation was derived from the Van der Waals equation. The original van der Waals parameters didn't give good description of vapor-liquid phase equilibria, which forced the user to fit the parameters to experimental results. Because of this, the model lost the connection to molecular properties, and therefore it has to be regarded as an empirical model to correlate experimental results. ==Equations== Van Laar derived the excess enthalpy from the van der Waals equation:〔The Open Thermodynamics Journal, 2010, 4, 129-140〕 :$H^=\; \backslash frac\; \backslash left(\; \backslash frac-\; \backslash frac\; \backslash right)^2$ In here ai and bi are the van der Waals parameters for attraction and excluded volume of component i. Since these parameters didn't lead to good phase equilibrium description the model was reduced to the form: :$\backslash frac=\; \backslash frac\; X\_2\}\; X\_2\}$ In here A12 and A21 are constants, which are obtained by regression of experimental vapor–liquid equilibrium data. The activity coefficient of component i is derived by differentiation to xi. This yields: :$$ \left\ \left( \frac X_2} \right)^2 \\ \ln\ \gamma_2=A_ \left (\frac X_2} \right)^2 \end\right. This shows that the constants A12 and A21 are equal to logarithmic limiting activity coefficients $\backslash ln\; \backslash left(\; \backslash gamma\_1^\backslash infty\; \backslash right)$ and $\backslash ln\; \backslash left(\; \backslash gamma\_2^\backslash infty\; \backslash right)$ respectively. The model gives increasing (A12 and A21 >0) or only decreasing (A12 and A21 <0) activity coefficients with decreasing concentration. The model can not describe extrema in the activity coefficient along the concentration range. In case $A\_=A\_=A$, which implies that the molecules are of equal size but different in polarity, then the equations become: :$$ \left\\right. In this case the activity coefficients mirror at x1=0.5. When A=0 the model the activity coefficients are unity, thus describing an ideal mixture. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Van Laar equation」の詳細全文を読む スポンサード リンク 翻訳と辞書 : 翻訳のためのインターネットリソース Copyright(C) kotoba.ne.jp 1997-2016. All Rights Reserved.