Giauque function

Discontinuities resulting from phase transitions in the reference elements can pose difficulties when interpolating from RHF-type tables, where enthalpies and free energies of formation are usually tabulated for temperature increments of 100°C. The problem can be circumvented to some extent by using the Gibbs energy function or Giauque function, —(G - H2 g)/T, which is listed in the fourth coltunn of these tables. The G and H symbols in this function refer to the absolute properties of the compound itself (not to the reference elements). Neither the G nor the H term is known, but the difference can be determined ( 7.5.4), and since 7/ 98 constant... 

Two other functions that allow calculation of high temperature AH and AG without the inconvenience of having phase transitions in the elements are the heat content (JTj. - H ) and the Gibbs energy or Giauque function Both of these... 

See W. F. Giauque and D. P. MacDougall, "Experiments Establishing the Thermodynamic Temperature Scale below 1 =K. The Magnetic and Thermodynamic Properties of Gadolinium Phosphomolybdate as a Function of Field and Temperature". J. Am. Chem. Soc., 60, 376-388 (1938). 

Figure 11.4. Heat capacities (excluding translation) for hydrogen (H2) gas as a function of temperature. Based on data of W. F. Giauque, J. Am. Chem. Soc. 52, 4816 (1930).

Making use of the data of Bodenstein and Lindner, as well as of some earlier investigators,50,363 Giauque and Kemp162 recalculated the thermodynamic functions and equilibrium constant for the reaction. Selected values from their results are shown in Table 4-2, along with... 

Roberts ( 1 1) surveyed the superconductive properties of the elements and recommended a critical temperature of 1.175 0.002 K for Al(cr). Since this temperature is so low, the effects of superconductivity on the thermodynamic functions are not considered. The entropy contribution due to superconductivity will be less than 0.002 J X mol . The data of Giauque and Meads (j ) and Downie and Martin (3) agree at temperatures up to 150 K but drift apart by 0.2 J X mol at 200 X and 0.17 J X mol at 300 K, with the Downie and Martin study being lower. The Takahashi (4, 5) study is even lower at 298 X. The high temperature heat capacity values are derived from the enthalpy study of Ditmars et al. (9). Their curve is intermediate between those derived from previous studies (4, 5, 6, 7, 8) and implies a flatter Cp curve near the melting point (in comparison to previous interpretations). Numerous other heat capacity and enthalpy studies are available but were omitted in this analysis. A detailed discussion of the Group IIIA metals (B, Al, and Ga) is in preparation by the JANAF staff. 

Giauque and Kemp (1.) calculated Idealized equilibrium constants for the reaction NgO (g) = 2 NO (g) from the work of Bodenstein and Boes (2), Verhoek and Daniels 3) and Wourtzel (4). The 2nd and 3rd law analysis of these equilibrium constants has been repeated using more recent functions. The results are shown below. 

The standard heat capacity derived by interpolation of the fitted C -functions is essentially equal to the value given by Busey and Giauque (17.13 cal mor -K ) who stated that near 300 K heat leaks may have introduced an error of several tenths of a percent into their -values. Thus the following value as well as its uncertainty are selected ... 

Busey and Giauque measured the heat capacity of nickel from 15 to 300 K. The entropy, heat content and free energy functions have been calculated. The authors used 99.98% nickel, in contrast to the numerous low temperature heat capacity studies quoted in this paper where rather low purity Ni-metal was investigated. Calculations of thermodynamic properties of nickel were extended to 800 K on the basis of available data. However, the results of such extrapolation seem to be less reliable. The standard molar entropy of Ni determined by Busey and Giauque was equal to 29.86 J-K -mol . ... 

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