Thermodynamics data table, chemical elements

This is the seventh volume of a series of expert reviews of the chemical thermodynamics of key chemical elements in nuclear technology and waste management. This volume is devoted to the inorganic species and compounds of selenium. The tables contained in Chapters 111 and IV list the currently selected thermodynamic values within the NEA-TDB Project. The database system developed at the NEA Data Bank, see Section 11.6, assures consistency among all the selected and auxiliary data sets. 

In thermodynamic data tables (standard enthalpies or Gibbs energies of formation and standard molar entropies) which relate to compounds other than ions in a solution, the common convention that is applied involves setting the values of standard enthalpy and standard Gibbs energy of formation (or chemical potential) equal to OJmor for all simple pure elements in their stable physical state at the temperature in question. The data therefore refer to the formation of substances from simple elements. 

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. 

Crystal field theory is one of several chemical bonding models and one that is applicable solely to the transition metal and lanthanide elements. The theory, which utilizes thermodynamic data obtained from absorption bands in the visible and near-infrared regions of the electromagnetic spectrum, has met with widespread applications and successful interpretations of diverse physical and chemical properties of elements of the first transition series. These elements comprise scandium, titanium, vanadium, chromium, manganese, iron, cobalt, nickel and copper. The position of the first transition series in the periodic table is shown in fig. 1.1. Transition elements constitute almost forty weight per cent, or eighteen atom per cent, of the Earth (Appendix 1) and occur in most minerals in the Crust, Mantle and Core. As a result, there are many aspects of transition metal geochemistry that are amenable to interpretation by crystal field theory. 

In (16), n is the number of electrons transferred in the overall process to maintain electroneutrality. Thermodynamic data for many chemical reactants and compounds are available as standard enthalpies A iFj ( and entropies S j-1 from thermodynamic tables in handbooks, for example, [53, 54], For the elements and for the proton H+ (aq) in aqueous solution (H30+), the AFl j-( values are zero by definition. Thermodynamic data for some typical electrochemical reactants are given in Table 2. 

Only K, B, H, S and R were used as sourees of data for simple oxides, oxohydroxides and hydroxides. Specialized databases created primarily for mineralogists and geologists report on thermodynamic data for materials of their special interest, e.g. natural silicates and aluminosilicates. These databases were used to complete data which were not available in K, B, H, S or R. Ref. [14] abbreviated as C does not directly list G° or AGf values. The G° values were calculated from Eq. (2.28) using the S taken from C. Then, Eq. (2.26) was applied to calculate AGf (compound) and the values of G° (elements) were taken from K. Then, data from Ref, [15] abbreviated as P were used. A few chemical formulas in P have typographical errors, which have been corrected in Table 2.2. The G° values were... 

In practice, G and H for a substance are defined relative to the G and H for the constituent elements. These relative values are known as free energy of formation and enthalpy of formation for standard conditions and referred to as AG° and AH°. Values for these functions may be obtained from standard tables of thermodynamic data, usually for the reference temperature of 298.2 K. The Chemical... 

Wagman, D. D., The NBS Tables of Chemical Thermodynamic Properties, J. Phys. Chem. Ref. Data 11, and supplements (1982) Barin, I. and Knacke, O., Thermochemical Properties of Inorganic Substances, Springer, Berlin (1983) Huitgren, R., Selected Values of the Thermodynamic Properties of the Elements, Am. Soc. for Metals, Metals Park, OH (1973)... 

In the last decade, quantum-chemical investigations have become an integral part of modern chemical research. The appearance of chemistry as a purely experimental discipline has been changed by the development of electronic structure methods that are now widely used. This change became possible because contemporary quantum-chemical programs provide reliable data and important information about structures and reactivities of molecules and solids that complement results of experimental studies. Theoretical methods are now available for compounds of all elements of the periodic table, including heavy metals, as reliable procedures for the calculation of relativistic effects and efficient treatments of many-electron systems have been developed [1, 2] For transition metal (TM) compounds, accurate calculations of thermodynamic properties are of particularly great usefulness due to the sparsity of experimental data. 

As the Gibbs function is a thermodynamic property, values of AG do not depend on the intermediate chemical reactions that have been used to transform a set of reactants, under specified conditions, to a series of products. Thus, one can add known values of a Gibbs function to obtain values for reactions for which direct data are not available. The most convenient values to use are the functions for the formation of a compound in its standard state from the elements in their standard states, as given in Tables 7.2... 

When this package is loaded, all the species data on 199 reactants and the 11A functions under this package will be available for calculations. Each chapter should be opened in a fresh workspace. A whole chapter can be run by use of Kemel/Evaluation/Evaluate Notebook. The properties for adenosine triphosphate are named atpsp, atp, atpNH, atpGT, atpHT, atpST, and atpNHT. These functions are all protected that is, none of them can be changed without unprotecting them. These thermodynamic values are based on the usual conventions of chemical thermodynamic tables that Af G = Af H = 0 for elements in defined reference states and for H" (a=l). 

Selenium forms compounds with most elements of the Periodic Table. NEA-TDB selected data for a number of these elements are not available for use as auxiliary data in the evaluation of formation data and entropies of their selenium compounds from reaction data. It would not have been a realistic task for the selenium project to assess all non-selected auxiliary data needed according to the NEA-TDB Guidelines. Instead the information required was obtained from compilations of thermochemical data such as The NBS tables of chemical thermodynamic properties and JANAF thermochemical tables supplemented by Critical reviews of. .. published in chemical Journals. The review of the literature on selenium and its compounds has thus resulted in two thermochemical data sets. One set of data is in accord with the NEA-TDB Guidelines and compatible with the requirements for addition to the NEA-TDB Data Bank. The other set, obtained with non-TDB auxiliary data, does not fulfil the requirements of the Data Bank. These facts created a problem in the presentation of the results of the selenium project, which was solved by the... 

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