Thermochemical properties data sources

The data in this appendix have been compiled from a number of sources. Nearly all of the critical property data are taken from Appendix A of The Properties of Gases and Liquids, Second Edition, by R. C. Reid and T. K. Sherwood, copyright 1966, McGraw-Hill Book Company. They are used with the permission of McGraw-Hill Book Company. Most of the thermochemical data (AG°, AH°f, and S°) were obtained from the following sources. 

We will now consider a practical example of calculating thermochemical properties for the species CH3. Actually a lot is known about the CH3 radical, and we choose it as example in order to compare the calculated results with experimental data. The NIST-JANAF Thermochemical Tables [62] are a standard source for experimental thermochemical data, as well as moments of inertia, vibrational frequencies, and the like. The NIST-JANAF Tables use the same basic approach outlined here to calculate the temperature dependence for their thermodynamic data, based on species vibrational frequencies and moments of inertia. 

Thermodynamic properties of molecular species that are used in reactor design problems can be readily estimated from thermodynamic data tabulated in standard reference sources such as Perry s Handbook or the JANAF Tables. Thermochemical properties of molecular species not tabulated can usually be estimated using group contribution methods. Estimation of activation energies is, however, much more difficult due to the lack of reliable information on transition state structures, and the data required to cany out these calculations is not readily available. 

The reason for the chemical vulnerability of phases based on copper oxides is shown in Fig. 1, which is a display of the heat of formation per gram-atom of the most stable solid oxides formed by the metallic and semiconducting elements in the periodic table. To generate this table, compilations of thermochemical data were consulted (23), and these sources provided the enthalpies of formation used for the calculations presented later. The reason for expressing the data in the manner shown in Fig.l is to get an idea of the relative strengths of the M-O bonds that form the solid oxides. One can see immediately that very few elements form weaker bonds with O than does Cu. Thus, most elements will reduce CuO to elemental Cu, and are very likely to react chemically with any of the copper-oxide superconductors as well. Although a positive heat of reaction, determined for interactions of the 1-2-3 superconductors with another material, is not a sufficient condition for chemical stability, it is almost certainly necessary. Consequently, researchers interested in the processing of copper-oxide superconductors into structures should consider thermochemical properties carefully. 

There are many other systems, particularly those important in the processing of inorganic materials, that could potentially be modeled with similar success using detailed chemical kinetic modeling. However, in these cases we generally have very few experimentally measured rate parameters and may not even have experimentally determined thermochemical properties (enthalpy of formation, standard entropy, etc.) for many of the important chemical species. While experiments are still the most reliable source for most of the needed data, they are also in many... 

As illustrated in Fig. 1, there are essentially four methods for obtaining thermochemical data for the species in our reaction mechanism. The first choice is to find the needed data in databases or in the literature in general. This includes both published experimental data and published quantum chemical calculations, which can also be a reliable source of thermochemical data. If no information on a substance is available in the literature, one should consider whether it can be treated by group additivity methods. If a well-constructed group additivity method is available for the class of molecules of interest, the results, which can be obtained with minimal effort, will be comparable in accuracy to those from the best quantum chemistry calculations. If group additivity is not applicable to the molecules of interest, then we may want to carry out quantum chemistry calculations for them, as discussed in detail in an earlier chapter. In some cases, the effort required to carry out the quantum chemical calculations may not be warranted, and we may want to make coarser, empirical estimates of thermochemical properties. 

The first place that one should generally look for thermochemical data is in the NIST Chemistry Web Book [24], available at http // webbook.nist.gov. This database contains thermochemical properties for more than 7000 small organic and inorganic compounds, and includes the entire contents of several other databases. Table 5 shows the enthalpies of formation and standard entropies of the species from the reaction mechanism in Table 4 that are available in the NIST WebBook. These properties were available for 10 of the 15 species. The source cited in the NIST WebBook for all these species was the NIST-JANAF Themochemical Tables [25], which have long been the first choice for finding thermochemical data for inorganic and very small organic... 

Another valuable source is the thermochemical property database assembled by Burcat and Ruscic [29], which is available online at ftp // ftp.technion.ac.il/pub/supported/aetdd/thermodynamics/. This collection is regularly updated by Prof. Burcat. It contains data for 1500 species, presented in the form of polynomial coefficients that can be used to compute the enthalpy, entropy, and heat capacity as a function of temperature. While Burcat s tables include a number of aluminum-oxygen compounds, they do not happen to include the aluminum-chlorine species that we have been using as an example. Of course, there are many other handbooks and compilations of thermodynamic properties. However, the vast majority of these focus on organic compounds and/or condensed phase species. Standard handbooks, such as the CRC Handbook of Chemistry and Physics, rarely have any information not included in the sources cited above. 

The standard enthalpies of sublimation of rare-earth metals have been measured by a number of workers. Hultgren et al. (1973) have discussed the sources of data and error estimates in their tabulation. Later Morss (1976) has also briefly discussed these data in his comprehensive discussion on thermochemical properties of the lanthanides. Recently Bratsch and Lagowski (1985) have listed a set of values of the sublimitation enthalpies which are also listed in table 1. The values of AH°f for rare-earth metals recommended in table 1 have been used in the recalculation of D values. 

When making combustion calculations one usually needs in addition to the thermochemical properties of the stable organic molecules those of organic radicals or even ions. Unfortunately, in this domain there are very few sources of data. 

The needed thermochemistry for many thousands of molecules is available from standard sources such as the JANAF tables. " Polynomial fits of this data in the form required by our kinetics software are also available. However, experimental thermochemical data is often lacking for many of the intermediate species that should be included in a detailed kinetics mechanism. Standard methods have been developed for estimating these properties, discussed in detail by Benson. ... 

The procedure of Lifson and Warshel leads to so-called consistent force fields (OFF) and operates as follows First a set of reliable experimental data, as many as possible (or feasible), is collected from a large set of molecules which belong to a family of molecules of interest. These data comprise, for instance, vibrational properties (Section 3.3.), structural quantities, thermochemical measurements, and crystal properties (heats of sublimation, lattice constants, lattice vibrations). We restrict our discussion to the first three kinds of experimental observation. All data used for the optimisation process are calculated and the differences between observed and calculated quantities evaluated. Subsequently the sum of the squares of these differences is minimised in an iterative process under variation of the potential constants. The ultimately resulting values for the potential constants are the best possible within the data set and analytical form of the chosen force field. Starting values of the potential constants for the least-squares process can be derived from the same sources as mentioned in connection with trial-and-error procedures. 

The choice of a given database as source of auxiliary values may not be straightforward, even for a thermochemist. Consistency is a very important criterion, but factors such as the publication year, the assignment of an uncertainty to each value, and even the scientific reputation of the authors or the origin of the database matter. For instance, it would not be sensible to use the old NBS Circular 500 [22] when the NBS Tables of Chemical Thermodynamic Properties [17], published in 1982, is available. If we need a value for the standard enthalpy of formation of an organic compound, such as ethanol, we will probably prefer Pedley s Thermodynamic Data and Structures of Organic Compounds [15], published in 1994, which reports the error bars. Finally, if we are looking for the standard enthalpy of formation of any particular substance, we should first check whether it is included in CODATA Key Values for Thermodynamics [16] or in the very recent Active Thermochemical Tables [23,24],... 

Burcat [ Thermochemical Data for Combustion Calculations, in Combustion Chemistry. (W. C. Gardiner, Jr., ed.), Chapter 8. John Wiley Sons, New York, 1984] discusses in detail the various sources of thermochemical data and their adaptation for computer usage. Examples of thermochemical data tit to polynomials for use in computer calculations are reported by McBride, B. J Gordon, S., and Reno, M. A., Coefficients for Calculating Thermodynamic and Transport Properties of Individual Species, NASA, NASA Langley, VA, NASA Technical Memorandum 4513, 1993, and by Kee, R. J., Rupley, F. M and Miller, J. A., The Chemkin Thermodynamic Data Base, Sandia National Laboratories, Livermore, CA, Sandia Technical Report SAND87-8215B, 1987. 

Data for other substances can be obtained from the following critical compilations and online in the NIST Chemistry WebBook at http //www.webbook.nist.gov/ chemistry/ or from the NIST-TRC Databases available on disk. (Information can be found at http //www.nist.gov/srd/thermo.htm, or at http //srdata.nist.gov/ gateway/gateway keyword = thermodynamics.) An exhaustive list of earlier sources of tabulated thermochemical data can be found in Volume 1 of Chemical Thermodynamics, A Specialist Periodical Report [2]. A useful list of websites containing thermodynamic data is available at http //tigger.uic.edu/ mansoori/ Thermodynamic.Data. and.Property.html. 

Thermochemical information was acquired from standard sources, where these were available. However, such data for some of the species in the mechanism have not been documented consequently, they were estimated using methods described in this paper. Physical molecular properties were either acquired from conventional sources (Hirschfelder et ai, 1954 Svehla,... 

For the diligent reader, thermochemical conventions are well-discussed in D. D. Wagman, W. H. Evans, V. B. Parker, R. H. Schumm, I. Halow, S. M. Bailey, K. L. Churney and R. L. Nuttall, The NBS Tables of Chemical Thermodynamic Properties Selected Valuesfor Inorganic and C, and C2 Organic Substances in SI Units , J. Phys. Chem. Ref. Data, 11 (1982), Supplement 2. However, the various subtleties expressed in this source, such as the above-cited ambiguities in temperature and pressure, have but negligible effect on any of the conclusions about cyclopropane and its derivatives in this chapter the data are too inexact and the concepts we employ are simply too sloppy to be affected. 

Gas-phase methods also constitute a source of important information on basic physical properties of silylenium ions. In particular, the thermochemical behavior is well characterized (30,33,34,47,61). Thermochemical data are applied for the evaluation of relative thermodynamic reactivities of silylenium ions in some systems. For example, affinities of R3Si+ and R3C+ toward various bases may be compared as the heterolytic dissociation energies of corresponding bonds [Eq. (12)] (47,61). It was shown that... 

At the time of publication this seven volume series was the most comprehensive source of thermochemical and other data in existence. Essentially all equilibrium and transport properties and classes of materials were covered. 

Finally, detailed appendices provide additional information (e.g., properties of the pure chemical elements, thermochemical data, crystallographic calculations, radioactivity calculations, prices of metals, industrial minerals and commodities), and an extensive bibliography completes this comprehensive guide. The comprehensive index and handy format of the book enable the reader to locate and extract the relevant information quickly and easily. Charts and tables are all referenced, and tabs are used to denote the different sections of the book. It must be emphasized that the information presented here is taken from several scientific and technical sources and has been meticulously checked and every care has been taken to select the most reliable data. 

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