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.

Second Law and Non-Equilibrium Entropy of Schottky Systems-Doubts and Verification.

Abstract: Meixner’s historical remark in 1969 “ it can be shown that the concept of entropy in the absence of equilibrium is in fact not only questionable but that it cannot even be defined” is investigated from today’s insight Several statements—such as the three laws of phenomenological thermodynamics, the embedding theorem and the adiabatical uniqueness—are used to get rid of non-equilibrium entropy as a primitive concept In this framework, Clausius inequality of open systems can be derived by use of the defining inequalities which establish the non-equilibrium quantities contact temperature and non-equilibrium molar entropy which allow to describe the interaction between the Schottky system and its controlling equilibrium environment

High temperature 93Nb NMR and Raman spectroscopic investigation of the structure and dynamics of solid and liquid NbCl5-alkali chloride solutions

Abstract: Pure liquid niobium chloride and solid and liquid NbCl5-alkali chloride solutions were for the first time studied by 93Nb NMR. Chemical shift (δ) and line width (Δν1/2) measurements were made by using a laboratory made probe head for experiments at elevated temperatures up to 650 °C. In the case of NbCl5-(LiCl/KCl)eut, where the salt mixture was not opaque, also Raman spectra could be recorded. For pure liquid NbCl5 the monomer–dimer equilibrium could be investigated. In the temperature range 200 °C to ca. 500 °C from the temperature dependence of both δ and Δν1/2 the equilibrium constant and the standard entropy and enthalpy for this reaction have been obtained. Binary NbCl5–CsCl and NbCl5–NaCl salt melts and solutions of NbCl5 in solid and liquid eutectic mixtures were investigated by 93Nb NMR. For some mixtures where the phase behaviour was only partially known, additional differential thermoanalysis (DTA) measurements of the phase diagrams have been performed. By 93Nb NMR a distinctly different behaviour of CsCl and NaCl containing melts is observed, where the the CsCl melts show relative broad resonance lines and a large negative chemical shift, whereas the NaCl melts reveal typically narrow lines and positive shifts. The broad lines are discussed with respect to the self-reduction reaction Nb5+ → Nb4+. In the high temperature solid phases of both NaCl and CsCl containing mixtures unusually narrow lines are explained by a fast ionic hopping process in these materials. The stability of oxy complexes in different salt matrices is also discussed. Finally, the observed temperature dependence of the 93Nb chemical shift (ca. 0.1 ppm K−1) in different salt mixtures is found to be in qualitative agreement with a theoretical estimate, which considers the Nb–Cl distance variation with temperature.

Empirical study of physicochemical and spectral properties of CuII-containing chelate-based ionic liquids.

Abstract: The physicochemical properties including melting point, density, viscosity, conductivity, and surface tension as well as spectral properties such as infrared and EPR spectra of the chelate-based ILs [Cnmim][Cu(F6-acac)3] (n = 6, 8, 10, 12, 14) were studied as functions of temperature and chain length. The thermodynamic properties such as the standard molar entropy and crystal energy were estimated by Glasser's theory, the molar enthalpy of vaporization was calculated by Kabo's method, and the ionicity was estimated by the Walden rule. Compared with the common ILs, the chelate-based ILs have larger molecular volume, larger density, smaller crystal energy, poorer ionicity and larger enthalpy of vaporization. The infrared spectra data of the ILs showed a red shift of the C-H bond stretching vibration of the alkyl chain in the cation and the EPR spectra showed that the crystal field of Cu2+ was kept when the chain length was elongated, which indicated the existence of microphase separation in the ILs. This work is helpful in understanding the structure-property relations of chelate-based ILs for further application.

Chapter 5 – Calorimetric Properties

Abstract: Publisher Summary This chapter deals with the calorimetric properties of polymers. The following properties belong to the calorimetric category: specific and molar heat capacities, latent heats of crystallization, or fusion. The specific heat capacity is the heat that must be added per kg of a substance to raise the temperature by one Kelvin or one degree Celsius. The molar heat capacity is the specific heat multiplied by the molar mass. Reliable values for the molar heat capacity in the solid and the liquid state are available for a limited number of polymers only. This emphasizes the importance of correlations between the chemical and the physical structure of polymers. The latent heat of fusion (crystallization) or the enthalpy difference is an important quantity for the calculation of other thermodynamic functions. Furthermore, knowledge of the latent heat of fusion is necessary for the design of a number of polymer processing apparatuses. Reliable experimental values for latent heat of fusion are available, however, for a limited number of polymers only. Based on this understanding, this chapter demonstrates that both groups of properties can be calculated as additive molar quantities. Finally, it suggests that starting from these properties the molar entropy and enthalpy of polymers can be estimated.