Deciphering the physical meaning of Gibbs’s maximum work equation

IF 1.8 3区 化学 Q1 HISTORY & PHILOSOPHY OF SCIENCE
Robert T. Hanlon
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引用次数: 0

Abstract

J. Willard Gibbs derived the following equation to quantify the maximum work possible for a chemical reaction

\({\text{Maximum work }} = \, - \Delta {\text{G}}_{{{\text{rxn}}}} = \, - \left( {\Delta {\text{H}}_{{{\text{rxn}}}} {-}{\text{ T}}\Delta {\text{S}}_{{{\text{rxn}}}} } \right) {\text{ constant T}},{\text{P}}\)

∆Hrxn is the enthalpy change of reaction as measured in a reaction calorimeter and ∆Grxn the change in Gibbs energy as measured, if feasible, in an electrochemical cell by the voltage across the two half-cells. To Gibbs, reaction spontaneity corresponds to negative values of ∆Grxn. But what is T∆Srxn, absolute temperature times the change in entropy? Gibbs stated that this term quantifies the heating/cooling required to maintain constant temperature in an electrochemical cell. Seeking a deeper explanation than this, one involving the behaviors of atoms and molecules that cause these thermodynamic phenomena, I employed an “atoms first” approach to decipher the physical underpinning of T∆Srxn and, in so doing, developed the hypothesis that this term quantifies the change in “structural energy” of the system during a chemical reaction. This hypothesis now challenges me to similarly explain the physical underpinning of the Gibbs–Helmholtz equation

\({\text{d}}\left( {\Delta {\text{G}}_{{{\text{rxn}}}} } \right)/{\text{dT}} = - \Delta {\text{S}}_{{{\text{rxn}}}} \left( {\text{constant P}} \right)\)

While this equation illustrates a relationship between ∆Grxn and ∆Srxn, I don’t understand how this is so, especially since orbital electron energies that I hypothesize are responsible for ∆Grxn are not directly involved in the entropy determination of atoms and molecules that are responsible for ∆Srxn. I write this paper to both share my progress and also to seek help from any who can clarify this for me.

解读吉布斯最大功方程的物理意义
J.威拉德-吉布斯(Willard Gibbs)推导出了以下等式,用于量化化学反应可能产生的最大功({\text{Maximum work }} = \, - \Delta {\text{G}}_{{\text{rxn}}}} = \, - \left( {\Delta {\text{H}}_{{\text{rxn}}}}{-}{text{ T}}\Delta {text{S}}_{{{text{rxn}}}}}\Right) {text{ constant T}},{text{P}}\)∆Hrxn是在反应量热计中测量的反应焓变,∆Grxn是在电化学电池中通过两个半电池上的电压测量的吉布斯能变化(如果可行的话)。对吉布斯来说,反应的自发性与 ∆Grxn 的负值相对应。但是,T∆Srxn(绝对温度乘以熵的变化)又是什么呢?吉布斯指出,这个术语量化了在电化学电池中保持恒温所需的加热/冷却。为了寻求比这更深层次的解释,即涉及导致这些热力学现象的原子和分子行为的解释,我采用了 "原子优先 "的方法来破解 T∆Srxn 的物理基础,并由此提出了一个假设,即这个术语量化了化学反应过程中系统 "结构能 "的变化。现在,这一假设向我提出了挑战,要求我同样解释吉布斯-赫尔姆霍兹方程(Gibbs-Helmholtz equation)的物理基础。\虽然这个等式说明了 ∆Grxn 和 ∆Srxn 之间的关系,但我不明白这是怎么回事,尤其是我假设对 ∆Grxn 起作用的轨道电子能量并不直接参与对 ∆Srxn 起作用的原子和分子的熵决定。我撰写这篇论文,既是为了分享我的研究进展,也是为了寻求任何能够为我澄清这个问题的人的帮助。
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来源期刊
Foundations of Chemistry
Foundations of Chemistry HISTORY & PHILOSOPHY OF SCIENCE-
自引率
22.20%
发文量
35
期刊介绍: Foundations of Chemistry is an international journal which seeks to provide an interdisciplinary forum where chemists, biochemists, philosophers, historians, educators and sociologists with an interest in foundational issues can discuss conceptual and fundamental issues which relate to the `central science'' of chemistry. Such issues include the autonomous role of chemistry between physics and biology and the question of the reduction of chemistry to quantum mechanics. The journal will publish peer-reviewed academic articles on a wide range of subdisciplines, among others: chemical models, chemical language, metaphors, and theoretical terms; chemical evolution and artificial self-replication; industrial application, environmental concern, and the social and ethical aspects of chemistry''s professionalism; the nature of modeling and the role of instrumentation in chemistry; institutional studies and the nature of explanation in the chemical sciences; theoretical chemistry, molecular structure and chaos; the issue of realism; molecular biology, bio-inorganic chemistry; historical studies on ancient chemistry, medieval chemistry and alchemy; philosophical and historical articles; and material of a didactic nature relating to all topics in the chemical sciences. Foundations of Chemistry plans to feature special issues devoted to particular themes, and will contain book reviews and discussion notes. Audience: chemists, biochemists, philosophers, historians, chemical educators, sociologists, and other scientists with an interest in the foundational issues of science.
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