Thermodynamic data completeness

Flame Temperature. The adiabatic flame temperature, or theoretical flame temperature, is the maximum temperature attained by the products when the reaction goes to completion and the heat fiberated during the reaction is used to raise the temperature of the products. Flame temperatures, as a function of the equivalence ratio, are usually calculated from thermodynamic data when a fuel is burned adiabaticaHy with air. To calculate the adiabatic flame temperature (AFT) without dissociation, for lean to stoichiometric mixtures, complete combustion is assumed. This implies that the products of combustion contain only carbon dioxide, water, nitrogen, oxygen, and sulfur dioxide. 

Indirect methods used can profit by the thermodynamic data of a particular metal-hydrogen system. The determination of the H/Me ratio after complete desorption of hydrogen from a sample, despite an apparent simplicity of the method, gives adequate results only when the bulk metal sample was entirely saturated with hydrogen, and that is a very rare case. The metal catalyst crystallites can be saturated in a nonuniform way, not through their whole thickness. The surface of this polycrystalline sample varies to such extent in its behavior toward interaction with hydrogen that hydride forms only in patches on its surface. A sample surface becomes a mosaique of /3-hydride and a-phase areas (85). 

It is worth noting that although PuFg(c) has not been characterized pentavalent fluorocomplexes are well known. In the hexava-lent state only oxyfluorocomplexes are known. However, thermodynamic data on these species are almost completely lacking. The thermal decomposition study (42J of the quadrivalent complex (NH4)4PuF8 according to scheme (10)... 

When one considers the potential high-energy release on rupture of a carborane unit, together with the thermodynamic stability of combustion products, it is hardly surprising that there is a body of literature that reports on the use of carbo-ranes within propellant compositions. Their use in energetic applications is to be expected when the enthalpy of formation (AH/) data for the products of combustion for boron are compared to those of carbon. Thermodynamic data for the enthalpy of formation of o-carborane and of typical boron and carbon combustion products is shown in Table 4. Measurements of the standard enthalpy of combustion32 for crystalline samples of ortho-carborane show that complete combustion is a highly exothermic reaction, AH = — 8994 KJmol. ... 

Does the thermodynamic dataset contain the species and minerals likely to be important in the study A set of thermodynamic data, especially one intended to span a range of temperatures, is by necessity a balance between completeness and accuracy. The modeler is responsible for assuring that the database includes the predominant species and important minerals in the problem of interest. 

Note These data have been obtained from the complete thermodynamic data tabulated in Kubaschewski et al. (loc. cit.), with the approximation of the simple two-term equation. This should serve for calculations not requiring an accuracy of better than 2kJmol 1 02, which is normally the case for industrial applications. Solid state crystal transformations which usually only have relatively small heats of transformation, have been ignored. 

These values of AG, AH and AS relate to a complete cell, because thermodynamic data cannot be measured experimentally for halfcells alone. 

No No Catalyst C added No reaction when Reactants A and B are mixed if Catalyst C is added after the entire charge of Reactants A and B has been completed, a rapid and violent reaction can occur Develop kinetic and thermodynamic data on this reaction... 

To illustrate the use of our thermodynamic treatment for concentrated systems, we have selected the system HC1-NaCl-H20 where there are complete and precise thermodynamic data for the ternary system and the constituent binaries from low molality... 

Representative heats of formation predicted by the ECP/BAC-MP4 method are given in Table 1 (the complete published [88] thermodynamic data set used in the analyses below is available online [91]). Data are shown for a range of compoimds, including tetravalent, trivalent, and divalent coordination at tin. Values for the reference compounds SnCU, SnH4, and Sn(CH3)4 are also given. Finally, heats of formation for atoms and groups needed to calculate reaction enthalpies are given. These results are used in the analysis below to identify potential reaction pathways for MBTC and its decomposition products. 

Tables of thermodynamic data necessary to apply equations listed by Cook are given in Appendix II of his book. The complete solution of the thermohydrodynamic theory for condensed explosives may then be effected in principle by a simultaneous solution of eqs...

An indication of the degree of exothermicity of sulphide oxidation reactions can be gained by comparing the enthalpy of formation (A//f), that is, a measure of the energy locked up in each chemical species, relative to native elements. The difference in enthalpies of formation of all reactants and all products defines the enthalpy (heat released or absorbed) of the reaction. Thermodynamic data on sulphide minerals, such as pyrite, are notoriously varied and disputed, and the values in Table 4 must be treated with caution. Nevertheless, depending on whether one defines the reaction as ending in an aqueous solution (equation 5), an intermediate secondary sulphate (e.g., melanterite - equation 6) or in complete oxidation to an oxyhydroxide (equation 7), the calculated reaction enthalpy (AH°) released is of the order of at least 1000 kJ/mol. 

Besides equilibriumconstants, additional thermodynamic data were included, if available, although little emphasis was put on their completeness. The data for primary master species comprise the standard molar thermodynamic properties of formation from the elements (AfG standard molar Gibbs energy of formation AfH°m standard molar enthalpy of formation ApSm- standard molar entropy of formation), the standard molar entropy (5m), the standard molar isobaric heat capacity (Cp.m), the coefficients Afa, Afb, and Afc for the temperature-dependent molar isobaric heat capacity equation... 

Presently, thermodynamic data bases for environmental chemistry are far from being complete. We believe that many built-in data bases of geochemical codes that include an impressive number of data for aqueous species and solid phases for most elements may easily produce incorrect results if used without criticism. Indeed, one of the main lessons learnt during our update exercise is that completeness and reliability of the data are mutually exclusive. On the other hand, reducing the data base to a small number of best thermodynamic data severely limits its field of applicability. Thus, in order to model specific systems of fundamental relevance for radioactive waste disposal we were forced to make compromises and had to include estimated constants. 

To conclude, we see the recent update of the Nagra/PSI data base as a small, but important, step towards completeness and reliability of the large body of thermodynamic data needed to calculate chemical equilibrium in the complex geochemical systems occurring within or in the vicinity of radioactive waste disposal sites. The most important achievement in this exercise was probably the elimination of a conspicuous number of thermodynamic data not supported by experimental evidence or of dubious origin. This sieving procedure resulted in a reduced, but at least transparent and self-consistent data base. Future extensions can now be built on this well-documented basis. 

The observed differences between the elements could presumably be attributed to differences in sorption properties of the chemical species present. Unfortunately, with the possible exception of Np, the lack of a complete set of thermodynamic data precludes a quantitative prediction of the concentrations of the various possible species in solution or of the conditions for the formation of solid phases. However, our data suggest that precipitation or colloid formation were the major reactions of Pu, Am and Cm in our solutions and, perhaps, a minor reaction of U. 

Although the entire discussion of electrochemistry thus far has been in terms of aqueous solutions, the same principles apply equaly well to nonaqueous solvents. As a result of differences in solvation energies, electrode potentials may vary considerably from those found in aqueous solution. In addition the oxidation and reduction potentials characteristic of the solvent vary with the chemical behavior of the solvent. as a result of these two effects, it is often possible to carry out reactions in a nonaqueous solvent that would be impossible in water. For example, both sodium and beryllium are too reactive to be electroplated from aqueous solution, but beryllium can be electroplated from liquid ammonia and sodium from solutions in pyridine. 0 Unfortunately, the thermodynamic data necessary to construct complete tables of standard potential values are lacking for most solvents other than water. Jolly 1 has compiled such a table for liquid ammonia. The hydrogen electrode is used as the reference point to establish the scale as in water ... 

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