Abstract

While analyses based on the Arrhenius kinetic model have been successfully applied since its introduction, the Arrhenius model neglects to describe pre-exponential factor in a scientifically meaningful fashion. Since the 1930s, transition-state theory (TST), has met with success in interpreting the pre-exponential factor’s value, allowing a standard entropy of activation to be estimated. However, analyses based on TST’s assumptions have been applied inconsistently in the literature, particularly in corrosion science, leading to difficulty in comparison of standard entropy of activations from different studies. In this work, the foundational principles of TST and standard states are discussed and a standard method to apply TST in analyzing rates of surface reactions is recommended. When full details are not available, reacting species’ concentrations should be normalized to the concentration of active surface sites. For corrosion reactions, conversion relationships are given to convert from units of corrosion rate to surface reaction rate, consistent with TST. This method is dubbed a surface reactant equi-density approximation. Application of this standard to reported data results in adjustments of the standard entropy of activation between − 65 and +50 J/mol K and brings reported entropies into a narrower range of values.

中文翻译：

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从动力学速率中提取表面反应的有意义的标准焓和活化熵

摘要

自引入以来，基于Arrhenius动力学模型的分析已成功应用，但Arrhenius模型却忽略了以科学有意义的方式描述指数前因子。自1930年代以来，过渡状态理论（TST）在解释指数前因子的值方面取得了成功，从而可以估计激活的标准熵。但是，基于TST假设的分析在文献中，尤其是在腐蚀科学中的应用不一致，导致难以比较来自不同研究的活化的标准熵。在这项工作中，讨论了TST和标准状态的基本原理，并推荐了将TST用于分析表面反应速率的标准方法。如果没有完整的详细信息，反应物质的浓度应归一化为活性表面部位的浓度。对于腐蚀反应，给出转换关系以将腐蚀速率单位转换为表面反应速率，与TST一致。该方法被称为表面反应物等密度近似。将此标准应用于报告的数据会导致激活的标准熵在-65至+50 J / mol K之间进行调整，并使报告的熵处于较窄的值范围内。