Standard molar entropy

About: Standard molar entropy is a research topic. Over the lifetime, 1586 publications have been published within this topic receiving 29886 citations.

Temperature-dependent estimation of Gibbs energies using an updated group contribution method

Abstract: Reaction equilibrium constants determine the mass action ratios necessary to drive flux through metabolic pathways. Group contribution methods offer a way to estimate reaction equilibrium constants at wide coverage across the metabolic network. Here, we present an updated group contribution method with: 1) additional curated thermodynamic data used in fitting; and 2) capabilities to calculate equilibrium constants as a function of temperature. We first collected and curated aqueous thermodynamic data, including reaction equilibrium constants, enthalpies of reaction, Gibbs free energies of formation, enthalpies of formation, entropies change of formation of compounds, and proton and metal ion binding constants. We further estimated magnesium binding constants for 618 compounds using a linear regression model validated against measured data. Next, we formulated the calculation of equilibrium constants as a function of temperature and calculated necessary parameters, including standard entropy change of formation (∆ f S°) and standard entropy change of reaction (∆ r S°), using a model based on molecular properties. The median absolute errors in estimating ∆ f S° and ∆ r S° were 0.010 kJ/K/mol and 0.018 kJ/K/mol, respectively. The efforts here fill in gaps for thermodynamic calculations under various conditions, specifically different temperatures and metal ion concentrations. These results support the study of thermodynamic driving forces underlying the metabolic function of organisms living under diverse conditions.

Dilute Near‐Critical Solutions of Iodine in Xenon: Determination of V 2∞, S 2∞ and (δp/δx) V,T∞ from Solubility Data

Abstract: Using recently determined solubility data for solid iodine dissolved in near-critical xenon, we have calculated the partial molar entropy and volume of the solute. These quantities show a strong density dependence in the vicinity of the solvent critical point. The quantity (δp/δx)V,T' which does not show a strong divergence in the critical region, was also determined from experimental data. Two procedures have been employed to describe the latter quantity and the solubility itself. It is shown that a first order perturbation method may be employed to describe the observed behaviour with a cross intermolecular energy parameter, e12, which, for low densities becomes dependent on the fluid density, but not on the temperature. The PYLJ integral theory is shown to account very well for the data with the value of e12 obtained employing the Lorentz-Berthelot combining rule.

Thermodynamic equilibrium for the dehydration of 1-butanol to di-n-butyl ether

Abstract: The thermodynamic equilibrium of the bimolecular dehydration of 1-butanol to di-n-butyl ether (DNBE) and water in the liquid phase was studied. Equilibrium experiments were performed at 4 MPa and in the temperature range of 413–463 K over the ion exchange resin Amberlyst-70. The thermodynamic equilibrium for the side reactions (dehydration to 1-butene, olefins isomerization, olefins hydration and branched ether formation) was also studied. The equilibrium constant for the dehydration reaction of 1-butanol to di-n-butyl ether and water was found to be independent of the operating temperature, within the limits of the experimental error (±5.2%). The experimental equilibrium constants at 413–463 K allows to estimate the standard enthalpy change of reaction (ΔrH0(l) = −0.3 ± 2.9 kJ mol−1) and the standard entropy change of reaction (ΔrS0(l) = 26.8 ± 6.7 J mol−1 K−1). From these values the standard formation enthalpy (ΔfH0DNBE,(l)) and the molar entropy of DNBE (S0DNBE,(l)) at 298.15 K were computed to be −370.5 ± 10.9 kJ mol−1 and 408.3 ± 6.8 J mol−1 K−1, respectively.