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.

Experimental and Computational Studies on the Structural and Thermodynamic Properties of Two Sulfur Heterocyclic Keto Compounds

Abstract: The present work reports the standard (p° = 0.1 MPa) molar enthalpies of formation in the gaseous phase of thioxanthone, (91.9 ± 2.4) kJ·mol−1, and tetrahydrothio-γ-pyrone, (−164.6 ± 2.0) kJ·mol−1, at T = 298.15 K, derived from their standard molar energies of combustion and standard molar enthalpies of sublimation, measured by rotating-bomb combustion calorimetry and by the vacuum drop microcalorimetric technique, respectively. For comparison purposes, we performed additional standard ab initio molecular orbital calculations, using the G3(MP2)//B3LYP composite procedure, which were used for the calculation of the enthalpies of several homodesmotic reactions, allowing us to extract the standard molar enthalpies of formation, in the gaseous phase, of the two heterocycles considered in this work. The calculated results are in excellent agreement with the experimental data. The three-dimensional structure of the crystal tetrahydrothio-γ-pyrone was also determined by X-ray crystallography.

Far from equilibrium synthesis of small polymer chains and chemical evolution

Abstract: A number of simple models for the synthesis of small polymers are considered. The role of autocatalysis and primitive template processes is examined. It is shown that far from equilibrium such systems may exhibit multiple steady state or sigmoidal transitions, favouring the enhancement of the (oligomer/monomer) ratio in the medium. A thermodynamic analysis in the non-linear range shows that the molar entropy production passes through a maximum when the system undergoes the non-equilibrium transition. The results are discussed in connection with the problems of prebiotic synthesis and developmental biology.