Critical Evaluation Of Thermodynamic Properties Research Articles

Critical evaluation of thermodynamic properties of rare earth sesquioxides (RE = La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, Sc and Y)

In order to develop the thermodynamic database containing rare earth sesquioxides (RE2O3), accurate thermodynamic descriptions of all stable and metastable RE2O3 phases are required. Rare earth sesquioxides have five polymorphs, which are (from low to high temperature) the cubic phase (C), the monoclinic phase (B), the hexagonal phase (A), the high temperature hexagonal phase (H), and the high temperature cubic phase (X). However, the thermodynamic property data of all polymorphs available in the literature are insufficient. In particular, the thermodynamic data for the phases stable only at high temperatures and for metastable phases are not well investigated. In this study, all ∆H298Ko, S298Ko, CP (or heat content) and phase transition temperature (Ttr) data available in the literature for each rare earth sesquioxide were collected and critically evaluated based on the sample preparations, experimental procedures and characterization techniques. Relationships between ∆H298Ko, S298Ko, and Ttr against the ionic radii of the entire rare earth cations were then established and missing thermodynamic information was predicted based on the general trends. In these ways, the accurate and consistent Gibbs energies of all stable and metastable RE2O3 phases (RE = La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, Y and Sc) were prepared. These Gibbs energy data can be readily used for the development of a comprehensive thermodynamic database containing rare earth oxides.

Critical Evaluation of Thermodynamic Properties for Halobenzoic Acids Through Consistency Analyses for Results from Experiment and Computational Chemistry

Thermodynamic properties of the twelve monohalobenzoic acids are critically evaluated through the application of computational chemistry methods for the ideal-gas phase and thermodynamic consistency assessment of properties determined experimentally and reported in the literature, including enthalpies of combustion, enthalpies of sublimation, and enthalpies of fusion. The compounds of interest are the 2-, 3-, and 4-halo isomers of fluoro-, chloro-, bromo-, and iodobenzoic acids. Computations were validated by comparison with critically evaluated entropies and heat capacities in the ideal-gas state for benzoic acid, benzene, and some halobenzenes. Experimental enthalpies of formation for 2- and 3-bromobenzoic acids, measured by well-established research groups, are mutually inconsistent and further, are shown to be inconsistent with the computations and assessment in this work. Origins of the discrepancies are unknown, and recommended values for these compounds are based on computations and enthalpies of sublimation validated, in part, by a structure-property (i.e., group-additivity) analysis. Lesser, but significant, inconsistencies between experimental and computed results are demonstrated also for 3- and 4-iodobenzoic acids. The comparison of enthalpies of formation based on the experiment and computation for the ideal-gas state of 1- and 2-chloro-, bromo-, and iodonaphthalenes provides additional support for the findings for halobenzoic acids and also reveals some anomalous results in the experimental literature for chloronaphthalenes. Computations are discussed in detail to demonstrate the approach required to obtain optimal results with modern quantum chemical methods.

Enthalpies of formation of small free radicals and stable intermediates: Interplay of experimental and theoretical values

A set of small radicals SiF, SiCl, F– C O, C N–O , O 3H, NO 3, CH 2NC, CF 3O , and O 3 exhibit pronounced discrepancies between different experimental as well as experimental and calculated values of the respective enthalpies of formation Δ f H o(298.15). For stable molecules, this quantity is well established and reliable values are available. However, for free radicals and other short-lived intermediates, the situation is not nearly as favorable. Consequently, critical evaluation of thermodynamic properties of free radicals is necessary, both originating from experiment and computation. Calculated enthalpies of formation for the above systems are based on the ab initio methods G3MP2B3 and CCSD(T)–CBS (W1U) for which mean absolute deviations are known.

Critical evaluation of thermodynamic properties of mixing for solid cobalt-platinum alloys between 1000 and 1400 K

Critical evaluation of thermodynamic properties of mixing for solid cobalt-platinum alloys between 1000 and 1400 K