Thermochemical data, estimation evaluation

Andreeva and Karapet yants prepared crystalline bismuth selenite and measured in a calorimeter its enthalpy of dissolution in HN03(aq, 1 9) denoted sin. The enthalpies of dissolution of bismuth nitrate and selenious acid in the same solvent were also determined. The numerical values used in the thermochemical cycle in the paper indicate that the compound denoted there by Bi(N03)3(cr) is in fact Bi(N03)3-5H20 (cr). The data were evaluated on this assumption in Table A-47. The partial standard molar enthalpies of formation of H2O and HNO3 were estimated from [82WAG/EVA]. 

Regarding quality of the values listed. Dr. Barin has wisely relied heavily on critically evaluated data (CODATA and JANAF) in cases where such values are available. For other substances he has drawn on a wide variety of sources, including the USBM Bulletins, other compilations, the periodical literature, and his own estimation of some thermochemical data. As new measurements are made, and as new critical evaluations become available, many of the Barin tables will require revision, but this is a characteristic of any attempt to compile thermochemical data. Anyone making thermochemical calculations who insists on the best possible data, will use a compilation, such as that of Barin or JANAF, as a starting place, but he will then check the recent periodical literature for new measurements that may have rendered the compiled values obsolete. This in no way detracts from the value of the compilation by Dr. Barin, which offers a starting place that is far more comprehensive than others, particularly for those concerned with metallurgical and similar systems. 

CHETAH is a tool for the preliminary screening of the reactivity hazards of organic chemicals. The evaluation is based on pattern recognition techniques using experimental hazard data and estimated thermochemical data. 

Frurip, D.J., Freedman, E. and Hertel. G.R.. 1989, A new release of the ASTM CHETAH programme for hazard evaluation versions for mainframe and personal computer, Int Symp on Runaway Reactions. 39-51 (CCPS, AIChE, USA). Benson. S.W., 1976, Thermochemical Kinetics. Methods for the Estimation of Thermochemical Data and Rate Parameters. 2nd edition (Wiley). 

Parentheses indicate estimated values. Thermochemical data from J. A. Kerr and M. J. Parsonage, "Evaluated Kinetic Data on Gas Phase Addition Reactions" Butterworths, 1972... 

In place of using statistical mechanics formulas to evaluate one can estimate it by thermochemical arguments using procedures developed by Benson (1976) and co-workers. The value of this method is that with some intuition and practice one can make reasonable guesses of the transition structure, compute its entropy of formation, and thus find preexponential factors. As with TST generally, no prediction is made for the barrier height and so the activation energy must be taken from experiments. We present here an outline of the thermochemical data manipulations required in this formulation and illustrate them with an application. 

These values were compared with independent estimates of the °roor/ro ,ro values from thermochemical cycles, where data were available to evaluate them. In the case of di-cumyl peroxide, for example, the E° obtained experimentally differs from the result of a thermodynamic calculation by only 30 mV. It is of interest to note that the uncorrected a data would have led to °roor/rovro values only slightly negative to the corrected ones (0.06-0.07 V). The good agreement in these cases was used as the basis to support the use of the convolution approach to estimate °roor/rovro for systems where the necessary values for thermochemical estimates are not available. This has been particularly useful in the study of endoperoxides and was used to estimate the standard reduction potential of the antimalarial agent, artemisinin. ... 

The initial application of this cost methodology to the NHI processes was based on early versions of the thermochemical and high temperature electrolytic processes being evaluated by NHI. These estimates, which had to be based on preliminary data and therefore, contained a higher level of... 

---