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.

Entropy of Alloy Phases: A Macroscopic Perspective

Abstract: This study presents a comprehensive analysis of the entropy of condensed phases, its temperature, pressure, and composition dependence on a macroscopic correlative platform. Two principal contributions to total nonconfiguration entropy (ST) are outlined. They are: (i) the pure thermal (Sth) contribution arising from the isochoric temperature dependence of Gibbs energy (GT) and (ii) the elastic contribution (Sel) representing the dilatational volume effects. It is then argued that entropy variation among a group of alloy phases can be exclusively related to molar volume, only when both thermal pressure (pth) and thermal entropy terms assume common values for all members. This argument is extended to establish a linear relationship between transformation entropy (ΔStr) and transformation-induced volumetric strain (ΔVtr/V). The temperature and pressure dependencies of entropy have been discussed in terms of the complementing roles of Sth and Sel and simple approximations to these effects are suggested. A macroscopic power law relation for systematizing the standard entropy variation using a composite scaling parameter (MV2/3/Tm) has been proposed, and its validity is demonstrated for both solid and liquid metals. This power law correlation has been exploited to deduce the following outcome: (i) a simple approximation for the initial slope (dp/dTm) of p–Tm melting curve, (ii) self-consistent correlation of entropy with specific heat and Debye temperature, (iii) estimation of entropy of metastable phases, and (iv) correlating dilute solution entropy with volume effects of alloying.

Thermodynamic Property Values for Enzyme-catalyzed Reactions

Abstract: This chapter deals with how one can obtain values of thermodynamic properties – specifically the apparent equilibrium constant K’, the standard molar transformed Gibbs energy change DrG’, and the standard molar transformed enthalpy change DrH’ for biochemical reactions – and, in particular, for enzyme-catalyzed reactions. In addition to direct measurement, these property values can be obtained in a variety of ways: from thermochemical cycle calculations; from tables of standard molar formation properties; by estimation from property values for a chemically similar reaction or substance; by means of estimation by using a group-contribution method; by combining a known value of the standard molar enthalpy change DrH and an estimated value for the standard molar entropy change DrS in order to obtain the standard molar Gibbs energy change DrG for a given reaction; and by use of computational chemistry.

Specific heat and related properties of some AIIBIVC and AIBIIIC semiconducting compounds between 2 and 300 K

Abstract: From specific heat measurements of the ternary semiconducting compounds ZnSiP2, ZnSiAs2, CdGeAs2, CuGaSe2, and CuInTe2 Debye characteristic temperatures and standard entropy values are calculated within the temperature range from 2 to 300 K. Aus Messungen der spezifischen Warmekapazitat der ternaren halbleitenden Verbindungen ZnSiP2, ZnSiAs2, CdGeP2, CuGaSe2, und CuInTe2 werden Debyetemperaturen und Standardentropien im Temperaturbereich von 2–300 K berechnet.

A computational study of entropy rules for charged fullerenes

Abstract: Thermochemical data on fullerenes are relatively scarce. However, some thermochemical information can be derived from gas-phase experiments using the Knudsen cell mass spectrometry method. The third-law treatment can be carried out on the observed data, though one has to make the crucial presumption that the change in the thermodynamic potential ΔΦ T o in the course of the reactions considered is negligible: ΔΦ T o =0. It would be difficult to check the presumption directly in the experiment, but it can be checked computationally. Model reactions like C60+ 70 − = 60 − +70 are selected. The change in the thermodynamic potential ΔΦ T o and the change in the standard entropy ΔS T o are computed. For example, at a temperature of T=1000 K, the standard changes for the reaction evaluated using the SAM1 method are ΔΦ T o =1.513 cal/(mol K) and ΔS T o =−0.054 cal/(mol K). Overall, the computations support the critical thermodynamic presumption.

Thermodynamic Dissociation Constants of Propionic Acid in Water and 1-Propanol Mixtures between 303.15 and 323.15 K

Abstract: Thermodynamic dissociation constants (Ka) of propionic acid in 0, 5, 10 and 20 wt% 1propanol-water binary mixtures have been determined between 303.15 and 323.15 K. A conductometric method has been applied to measure the molar conductance of dilute solutions of propionic acid. Fuoss-Kraus conductance equation has been applied to calculate the values of limiting molar conductance (Λ0) and thermodynamic ionization constant (Ka). It was found that both the values of Ka and Λ0 decreased by the increasing of amount of 1-propanol in the binary mixtures. However, Ka values were decreased and Λ0 values were increased by increasing temperatures. The normalized Walden products of the propionic acid have been calculated. Thermodynamic quantities such as change of standard free energy (∆G°), change of standard enthalpy (∆H°) and change of standard entropy (∆S°) have been calculated in case of each of the binary mixtures.