Departamento de Química Analítica, Facultad de Química, UNAM, Ciudad Universitaria, Ciudad de México, México.
Crit Rev Anal Chem. 2023;53(4):775-797. doi: 10.1080/10408347.2021.1977609. Epub 2021 Oct 3.
A free energy-based conceptual theoretical framework from which the conditional equilibrium constant can be comprehensibly understood is presented. This constant is found to be a weighted geometric mean of the equilibrium constants of the reactions of all forms of the conditioned species under buffering conditions, where the weight is given by a function of their predominance in terms of their mole fractions. Once it is shown that this type of equilibrium constant can be easily deduced form free energy functions, it is shown how corrections for activity coefficient can be incorporated as well. The framework additionally permits to interpret side-reactions coefficients as free energy terms related to the chemical speciation of the system, allowing the use of the generalization of Hess' law to obtain conditional constants and a straightforward deduction of multiconditional equilibrium constants. Furthermore, different uses of the conditional constants along the actual literature are reviewed as well allowing to have a complete and updated panorama of the employment of this important concept in chemical and speciation analysis in many areas of research.
提出了一个基于自由能的概念理论框架，可以从中全面理解条件平衡常数。发现该常数是缓冲条件下所有形式的调节物种反应的平衡常数的加权几何平均值，其中权重由它们在摩尔分数方面的优势的函数给出。一旦表明这种类型的平衡常数可以很容易地从自由能函数中推导出来，就可以展示如何纳入活度系数的校正。该框架还允许将副反应系数解释为与系统化学形态有关的自由能项，从而可以使用赫斯定律的推广来获得条件常数，并直接推导出多条件平衡常数。此外，还回顾了条件常数在实际文献中的不同用途，从而可以全面了解和更新这一重要概念在化学和形态分析领域的许多研究领域中的应用。
