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.

Renormalized thermal entropy in field theory

Abstract: Standard entropy calculations in quantum field theory, when applied to a subsystem of definite volume, exhibit area-dependent UV divergences that make a thermodynamic interpretation troublesome. In this paper we define a renormalized entropy which is related with the Newton-Wigner position operator. Accordingly, whenever we trace over a region of space, we trace away degrees of freedom that are localized according to Newton-Wigner localization but not in the usual sense. We consider a free scalar field in d+1 spacetime dimensions prepared in a thermal state and we show that our entropy is free of divergences and has a perfectly sound thermodynamic behavior. In the high temperature/big volume limit our results agree with the standard QFT calculations once the divergent contributions are subtracted from the latter. In the limit of low temperature/small volume the entropy goes to zero but with a different dependence on the temperature.

Thermodynamics of non-stoichiometry A model for UCx

Abstract: The partial molar properties of carbon in UC x , 1·0 x 2·0, are described in terms of an f.c.c. lattice gas model in which the C2 groups attract only when they are nearest neighbours. A modified Monte Carlo method is used to calculate directly the chemical potential as a function of x and temperature. Satisfactory agreement is obtained between the calculated and experimental values of the partial molar entropy and enthalpy of carbon. The nearest neighbour interaction energy (attractive) is — 1·91 kcals mole−1 and was calculated from the critical temperature.

High temperature thermodynamic properties, orthorhombic/tetragonal transition and phase stability of GdBa2Cu3Oy and related R123 compounds

Abstract: Thermogravimetric measurements of the equilibrium oxygen partial pressure ( p (O 2 )) as a function of temperature and oxygen content have been made on GdBa 2 Cu 3 O y (Gd123) within the range 3×10 −4 atm≤ p (O 2 )≤1 atm and 450°C≤ T ≤800°C. The partial molar entropy Δ S (O 2 ) and enthalpy Δ H (O 2 ) of solution of oxygen in Gd123 are evaluated and discussed. The p (O 2 ) data on Gd123 are compared with measurements performed on NdBa 2 Cu 3 O y (Nd123) at 800°C and literature data for YBa 2 Cu 3 O y (Y123) at 600°C and 800°C. The orthorhombic/tetragonal transition temperature ( T O/T ) for Gd123 and Nd123 as a function of the oxygen partial pressure (1×10 −3 atm≤ p (O 2 )≤1 atm) has been determined by high temperature X-ray diffraction (HTXRD). The oxygen content values for the O/T transition ( y O/T ) at several p (O 2 ) values for Gd123 and Nd123 have been determined by means of thermogravimetric measurements. The obtained data in the y – T diagram supports the applicability of the quasichemical approximation in describing the O/T transition of Gd123 and Nd123 compounds. The effect of the R atom (R=Y, Gd, Nd) ionic size on the oxygen stoichiometry and phase stability of R123 compounds at high temperature is discussed, and a possible explanation is proposed which accounts for the lattice mismatch between Ba–O and CuO 2 layers.

The Dissociation of Ammonium Chloride

Abstract: Two values for the standard free energy of dissociation of ammonium chloride into ammonia and hydrogen chloride, calculated by two independent paths, are 21,860 cal. and 21,780 cal. at 298.1°K. The good agreement serves as additional evidence for the complete dissociation of ammonium chloride in the vapor phase. The corresponding values calculated for ΔH at 298.1 are 42,160 and 42,260 cal. Two independent values for the standard entropy of the aqueous ammonium ion at 298.1°K derived from these data are 26.5 and 27.1 cal. mole−1 deg.−1.