CODATA Tables

Chapters 3-5 have described the calculation of various transformed thermodynamic properties of biochemical reactants and reactions from standard thermodynamic properties of species, but they have not discussed how these species properties were determined. Of course, some species properties came directly out of the National Bureau of Standard Tables (1) and CODATA Tables (2). One way to calculate standard thermodynamic properties of species not in the tables of chemical thermodynamic properties is to express the apparent equilibrium constant K in terms of the equilibrium constant K of a reference chemical reaction, that is a reference reaction written in terms of species, and binding polynomials of reactants, as described in Chapter 2. In order to do this the piiTs of the reactants in the pH range of interest must be known, and if metal ions are bound, the dissociation constants of the metal ion complexes must also be known. For the hydrolysis of adenosine triphosphate to adenosine diphosphate, the apparent equilibrium constant is given by... 

It was not until the mid-1960s that Harrison Brown (later ICSU President) called attention to the absence of any successor to the International Critical Tables, and was asked by ICSU to make recommendations. This led to ICSU s creation of CODATA, following on from ICSU s earlier World Data Centers, devoted to specific sciences such as metereology. This body is more of a gadfly and organiser... 

Species N.B.S. Circ. 500 (1952) N.B.S. Tech. Note 270/3 (1969) JANAF Tables (1971) CATCH Tables (1972r CODATA Bulletins (1977, 1978) ... 

In fluorine thermochemistry, two key heat values frequently occur. They are the dissociation energy of difluorine, required for evaluation of fluorine bond energies and the heat of formation of hydrogen fluoride, a product in hydrolysis, hydrogenation, fluorine combustion, or neutralization reactions. These values have been difficult to measure and have changed considerably over the years. A recommended set of values has been reported in recent CODATA bulletins (60) which are collected in Table I together with older values and corrections to update them. 

Thus, errors in all the heats, apart from the precisely known water value, are decreased ra-fold in the required heat. The hydrolysis heat A//2 is always much less than At and can be measured less precisely. The reactions involved in reactions 2, 3, and 6 of Table II have been used in the CODATA evaluation of Aif,(F q)), although in theorv reactions 7 and 8 should lead to more accurate values. In practice this may not be true. Thus the fluorination of iodine produces some IF7, together with the bulk of IF5, and errors in estimating the mixture can cause uncertainty in the final value of AZf/IF ). The hydrolysis heat for the reaction... 

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],... 

There are several publications dealing with units and symbols of physical chemical quantities. Some also list the values of the fundamental physical constants, as recommended by the Committee on Data for Science and Technology (CODATA) in 2005 [1], The following tables contain the information that is relevant for molecular energetics [1,2]. 

When can a set of data be regarded as a database Guidelines such as the number of records or the publication medium may not be useful. CODATA values, for example, which are the recommended starting point for any database (or any thermochemical calculation, for that matter), involve only about 150 species. Also, the CODATA reports have been printed in regular scientific journals before the final set was released as a book and later posted on the Internet. Second, we could have distinguished between databases and data compilations. The former involve recalculation of quantities such as standard enthalpies of formation to ensure a consistent set of values (see section 2.5). Databases may also include data assessment, leading to recommended values. Data compilations, on the other hand, are just collections of literature values. Although this distinction is important (see table Bl), a data compilation can be rather useful for the expert user and save many hours of literature search. 

The Active Thermochemical Tables (ATcT) are the result of an effort to derive accurate, reliable, and internally consistent thermochemical values based on a thermochemical network approach. They contain data for over 350 compounds. Recommended values for key compounds such as CC>2(g), H20(g), and CH4(g) are slightly different from those given by CODATA. 

Table 4.1. Fundamental physical constants (adapted from Nist Codata, Mohr and Taylor (2005)).

We assume here that the Bohr magneton /zb is a positive quantity. The numerical value of the Bohr magneton and some other fundamental constants, as recommended by CODATA, the Committee on Data for Science and Technology of the international Council of Scientific Unions, are presented in Table 4.1 [103]... 

TABLE 8. CODATA values for Af//°(g,298) for halogens and hydrogen halides88... 

Garvin D., Parker V. B., and White H. J. (1987) CODATA Thermodynamic Tables—Selections for Some Compounds of Calcium and Related Mixtures A Prototype Set of Tables. Hemisphere Publishing Corp., Washington, DC, 356pp. 

Numerous new and revised thermochemical tables are included in this collection. However, this Third Edition is primarily a rewriting and a recalculation of all the tables no attempt has been made to reanalyze the data for all tables. The rewritten tables adhere more closely to the current lU-PAC recommendations on symbols and notation. The recalculated tables are all based on the current lUPAC and CODATA recommendations for relative molecular masses and fundamental constants. As a result, a comparison of a table in this Third Edition and its previously published form (i.e., same revision date) will reveal differences however, these result from the adjustments mentioned above rather than from a reanalysis of the data. 

The thermal functions at 298.15 K agree with recent CODATA recommendations (6) 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... 

H. J. White, Jr., Chairman, CODATA Task Group on Chemical Thermodynamic Tables, report to be published, 1985. 

JANAF values and uncertainties at 298.15 K are the same as those selected by CODATA (j ). Previous therraochemical tables based on direct-summation calculations of Woolley et al. (6) include that of Gurvich et al. (H ) and that of NBS-JANAF (9, 8). Differences of the new JANAF values from the NBS table are greatest near 5300 K, reaching maximum of 0.005 cal k" mol" in S and... 

The enthalpy of sublimation of magnesium is the enthalpy of formation of the gas. It is chosen to be that adopted by CODATA (6) based on numerous experimental studies which are discussed in the Mg(g) single phase table (14). 

The atomic energy levels have been taken from the compilation of Martin and Zalubas (J ). Our calculated values for the thermal functions are similar to those recommended by CODATA (1 ). They do differ for two reasons, however. First, the entropy differs by 0.1094 J K mol because this table uses a reference pressure of 1 bar, whereas the CODATA recommendations are based on 1 atm. Second, the entropies at 298.15 K for all alkali metal gases differs by 0.004 J K mol , presumably due to the use of slightly different values for auxiliary data. 

J. D. Cox, chairman, CODATA Task Group on Key Values for Thermodynamics, J. Chem. Thermodynamics J, 903 (1978). JANAF Thermochemical Tables P (g), 12-30-82. 

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