Affinity and Reaction Rate Close to Equilibrium

An improved version of the manometric apparatus and its procedures for measuring excess sorption of supercritical carbon dioxide are presented in detail with a comprehensive error analysis. An improved manometric apparatus is necessary for accurate excess sorption measurements with supercritical carbon dioxide due to the difficulties associated with the high sensitivity of density for pressure and temperature changes. The accuracy of the apparatus is validated by a duplicate measurement and a comparison with literature data. Excess sorption and desorption of CO 2 on Filtrasorb 400 at 318.11 K up to 17 069 mole/ m 3 ͑15.474 MPa͒ were selected for this validation. The measured excess sorption maximums are 7.79Ϯ 0.04 mole/ kg at 2253 mole/ m 3 for the first sorption isotherm and 7.91Ϯ 0.05 mole/ kg at 2670 mole/ m 3 for its subsequent desorption isotherm. The sorption and desorption peaks of the duplicate experiment are 7.92Ϯ 0.04 mole/ kg at 2303 mole/ m 3 and 8.10Ϯ 0.05 mole/ kg at 2879 mole/ m 3 , respectively. Both data sets show desorption data being higher than the sorption data of the same data set. The maximum discrepancy between the desorption and sorption isotherms of one data set is 0.15 mole/kg. The discrepancy between the two excess sorption isotherms is 0.12 mole/kg or less. The a priori error of the excess sorption measurements is between 0.02 and 0.06 mole/kg. The error due to He contamination is between 0.01 and 0.05 mole/kg. The difference between the a priori uncertainty and the observed maximum discrepancies is considered to be acceptable. The sorption isotherms show identical qualitative behavior as data in the literature. The quantitative behavior is similar but the peak height and the linear decrease in excess sorption at high gas densities are 10% higher. A plot of the excess sorption versus the density can be used to obtain the sorbed phase density and the specific micropore volume. These sorbed phase densities are in excellent agreement with the data in the literature. Furthermore, the excess sorption data scaled to this specific micropore volume in this work and in the literature collapse on a single curve when plotted versus gas density.

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“…This is in line with the suggestion by Prigogine et al 35 for the description of reaction rates near equilibrium. Combination results in with…”

Section: Appendix D: Demonstration Of the Negligibility Of The Influesupporting

confidence: 93%

Improved manometric setup for the accurate determination of supercritical carbon dioxide sorption

Hemert

Bruining

Rudolph

et al. 2009

Review of Scientific Instruments

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“…-De Donder and others have demonstrated that near equilibrium there is a simple proportional relation between the affinity and the rate of reaction [82][83][84]:…”

Section: Assumptions Of the Linear Response In Thermodynamicsmentioning

confidence: 99%

Macroscopic non-equilibrium thermodynamics in dynamic calorimetry

Garden

2007

Thermochimica Acta

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“…The last equation has also motivated the declaration of the affinity as a "thermodynamic driving force" for a chemical reaction, i. e. as a force determining its rate. The first relation, (1), is, in fact, a result of the entropic inequality (the second law of thermodynamics) and should be generally, for R reactions, formulated as follows:…”

Section: Introductionmentioning

confidence: 99%

“…However, there is no direct proof that each individual reaction from a system should satisfy an equation like (1). The only thermodynamic requirement for a system of reactions is (4) and all discussions on coupling against spontaneity are in this sense superfluous.…”

Section: Introductionmentioning

confidence: 99%

Affinity and Reaction Rates: Reconsideration of Theoretical Background and Modelling Results

Pekař

2009

Zeitschrift Für Naturforschung A

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The phenomenological affinity approach to chemical kinetics based on mass-action rate expression is revised. It is shown that the reaction rate is not an unambiguous function of affinity and that in ideal mixtures with only elementary reactions thermodynamic coupling, i. e. a positive reaction rate and negative affinity of some reaction step at the same time, is not possible. Neither does thermodynamic coupling occur in a non-ideal system of elementary reactions where the mass-action rate equation is written with activities in place of concentrations. The non-ideality and/or non-equality of reaction orders to stoichiometric coefficients lead to more complex affinity-rate relationships than commonly given which puts no explicit restrictions on affinity and rate signs. Theoretical considerations are completed with results of numerical modelling made on several simple mechanisms. Various combinations of affinity and rate signs and complex affinity-rate profiles were obtained. Modelling results support the idea that affinity is much more a result of the time evolution of a reacting system and corresponding time profiles of concentrations than the actual cause of reaction rates.

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Affinity and Reaction Rate Close to Equilibrium

Cited by 70 publications

References 4 publications

Improved manometric setup for the accurate determination of supercritical carbon dioxide sorption

Improved manometric setup for the accurate determination of supercritical carbon dioxide sorption

Macroscopic non-equilibrium thermodynamics in dynamic calorimetry

Affinity and Reaction Rates: Reconsideration of Theoretical Background and Modelling Results

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