Standards CODATA thermodynamic values

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],... 

Table IV-1 Selected thermodynamic data for auxiliary compounds and complexes adopted in the NEA-TDB project, including the CODATA Key Values [89COX/WAG]. All ionic species listed in this table are aqueous species. Unless noted otherwise, all data refer to 298.15 K and a pressure of 0.1 MPa and, for aqueous species, a standard state of infinite dilution (/ = 0). The uncertainties listed below each value represent total uncertainties and correspond in principle to the statistically defined 95% confidence interval. Values in bold typeface are CODATA Key Values and are taken directly from Ref [89COX/WAG] without further evaluation. Values obtained from internal calculation, cf. footnotes (a) and (b), are rounded at the third digit after the decimal point. Systematically, all the values are presented with three digits after the decimal point, regardless of the significance of these digits. The reference listed for each entry in this table indicates the NEA-TDB Review where the corresponding data have been adopted as NEA-TDB auxiliary data. The data presented in this table are available on computer media from the OECD Nuclear Energy Agency.

Although the focus of this review is on thorium, it is necessaiy to use data on a number of other species during the evaluation process that lead to the recommended data. These auxiliary data are taken both from the publication of CODATA Key Values [1989COX/WAG] and from the evaluation of additional auxiliary data in the other volumes of this series detailed above, and their use is recommended by this review. Care has been taken that all the selected thermodynamic data at standard conditions cf. Section II.3) and 298.15 K are internally consistent. For this purpose, special software has been developed at the NEA Data Bank that is operational in conjunction with the NEA-TDB data base system, cf. Section 11.6. In order to maintain consistency in the apphea-tion of the values selected by this review, it is essential to use these auxiliary data when calculating equilibrium constants involving thorium compounds and complexes. 

Section 5 Thermochemistry, Electrochemistry, and Kinetics CODATA Key Values for Thermodynamics Standard Thermodynamic Properties of Chemical Substances Thermodynamic Properties as a Function of Temperature Thermodynamic Properties of Aqueous Systems Heat of Combustion Electrical Conductivity of Water... 

Table 17.14 represents a listing of all actinide compounds and other species for which measured or estimated thermodynamic properties are available. The sequence of species is by actinide element, with subordinate elements following the US National Bureau of Standards standard order of arrangement. Original literature references have been cited, unless there is an authoritative review or assessment. Error limits are given wherever possible. This tabulation attempts to be self-consistent with the CODATA [128] thermodynamic compilations, and in general accepts IAEA assessments [14-21], which are consistent with CODATA-IUPAC selected data. In many cases for thorium and uranium compounds the NBS [12] tabulations were accepted it should be pointed out that the NBS compilation is self-consistent but not always contemporary and not in exact agreement with CODATA key values. Estimated values of thermodynamic properties are shown in parentheses. 

The thermodynamic functions at 298.15 K agree exactly with recent CODATA recommendations ( ) except for two minor differences. First, the entropy differs by 0.1094 J k" mol" because this table uses a standard-state pressure of 1 bar, whereas the CODATA recommendations are based on 1 atm. Second, entropy differences of the order of 0.001-0.004 J K" mol" for the rare gases arise due tO the use of slightly different values for R this table uses R 8.31441 J K" mol". Considering these minor... 

In every review of thermodynamic data care should be taken that the same and simultaneously the most reliable auxiliary quantities are employed. Consequently CODATA values (see NEA-TDB auxiliary data) were taken whenever they had been available. The standard enthalpy of formation and the partial molar entropy of the bivalent nickel... 

The following table lists values of fundamental physical constants used in thermodynamic calculations. Except for those marked exact, they are the 2006 CODATA (Committee on Data for Science and Technology) recommended values. The number in parentheses at the end of a value is the standard deviation uncertainty in the right-most digits of the value. 

It is regrettable that, in the past, different symbols have been adopted in compilations, but it is expected that, in the future, symbols advocated by I UP AC will be employed universally and that SI will be used for the units. To secure a further unification in thermodynamic tables, the International Council of Scientific Unions (ICSU) and the Committee on Data for Science and Technology (CODATA) set up in 1968 a Task Group on Key Values for Thermodynamics. The first objective of the Task Group is to prepare a set of values of the basic thermodynamic properties of a number of chemical species, to be agreed internationally. The set is to include the elements in both standard and monatomic gaseous states, aqueous ions, and simple compounds. ... 

---