Activity coefficient | EPFL Graph Search

In thermodynamics, an activity coefficient is a factor used to account for deviation of a mixture of chemical substances from ideal behaviour. In an ideal mixture, the microscopic interactions between each pair of chemical species are the same (or macroscopically equivalent, the enthalpy change of solution and volume variation in mixing is zero) and, as a result, properties of the mixtures can be expressed directly in terms of simple concentrations or partial pressures of the substances present e.g. Raoult's law. Deviations from ideality are accommodated by modifying the concentration by an activity coefficient. Analogously, expressions involving gases can be adjusted for non-ideality by scaling partial pressures by a fugacity coefficient. The concept of activity coefficient is closely linked to that of activity in chemistry. Thermodynamic definition The chemical potential, \mu_\mathrm{B}, of a substance B in an ideal mixture of liquids or an ideal solution

Influence of Uncertainties in pH, pMg, Activity Coefficients, Metabolite Concentrations, and Other Factors on the Analysis of the Thermodynamic Feasibility of Metabolic Pathways

Urs von Stockar

Thermodynamic feasibility analysis (TFA) has been used as a toot capable of providing additional constraints to the mass balance-based methods of analysis of Metabolic networks (e.g., flux balance analysis). Several publications have recently appeared in which TFA of different metabolic pathways from relatively simple to the genome-scale networks was described as a means of detecting the possible metabolic control steps. However, in order to perform TFA, many simplifying assumptions were necessary. On the other hand, it has been shown by applying TFA to the well-known pathway of glycolysis that erroneous simplifying assumptions may seriously bias the results of the analysis. A quantitative analysis of the influence of non-ideality of the biochemical system, pH, temperature, and complexation of the metabolites with Mg2+ ions as well as a number of other factors on the TFA is reported. It is shown that the feasibility of glycolysis is very seriously limited by the reaction of oxidative phosphorylation of glyceraldehyde phosphate, and that the intracellular concentration of the main product of this reaction, biphosphoglycerate, must be anywhere from 10 to 100 times lower than published values. In addition, the driving force for this reaction, and consequently the feasibility of the entire pathway depend strongly on the intracellular pH and ionic strength and to a lesser extent on pMg and temperature. The analysis may also be influenced by uncertainties of the dissociation and magnesium complexation constants of glyceraldehyde phosphate. The analysis demonstrates the crucial importance of taking such factors into account when performing TFA. It also suggests an urgent need for experimental determinations of such factors as a prerequisite for sensible thermodynamic analysis of metabolism on a genome-wide scale. Biotechnol. Bioeng. 2009;103: 780-795. (c) 2009 Wiley Periodicals, Inc.

2009

Introductory Thermodynamics

Pierre Infelta

The fundamental aspects of classical thermodynamics are presented in a simple compact way. The equations derived are illustrated by numerous (111) examples, often direct application of the relations just obtained. The (four) laws of thermodynamics are presented and illustrated. The need to define thermodynamic temperature, the meaning of auxiliary thermodynamic functions, the origin, usefulness and use of partial molar quantities are all examined. Gaseous systems, phase equilibriua and chemical reactions are quantitatively treated. It is shown how chemical reactions can provide work. Ideal and non ideal solutions are presented with the various standard states and activity coefficients. This book will be if use to a wide audience of students and professionals in the fields of Chemistry, Chemical Engineering, Materials Science and bio related sciences. "Dr. Infelta has prepared a compact Introductory Thermodynamics book which will serve well for mature students who need a command of this important field. Undergraduate students with confidence in their mathematical background will find the presentation logical, the examples thoughtful, and the coverage thorough. Students and professionals for whom memory or mastery of previous thermodynamics courses have dimmed, will find, in addition to the above virtues, careful derivation of the properties of non-ideal systems and emphasis on when to use these results instead of ideal system results, treatment of multireaction equilibria, and (a personal favorite) a succinct elucidation of that odd proposition of thermodynamics, Le Chatelier's Principle. These students will value this small volume packed with the power of classical thermodynamics." Lynn Melton, Professor of Chemistry, University of Texas, Dallas.

BrownWalker Press2004

Introductory Thermodynamics

Pierre Infelta

Overseas Press India Private Limited2006

Influence of Uncertainties in pH, pMg, Activity Coefficients, Metabolite Concentrations, and Other Factors on the Analysis of the Thermodynamic Feasibility of Metabolic Pathways

Urs von Stockar

2009