Contributions to the Data on Theoretical Metallurgy: [Part] 11. Entropies of Inorganic Substances: Revision (1948) of Data and Methods of Calculation Page: 55

ENTROPIES OF INORGANIC SUBSTANCES AT 298.160K.

IRIDIUM
Element.-The entropy of Ir(c), calculated by Lewis and Gibson
(331) from Dewar's (126) mean heat-capacity value, is adopted, the
uncertainty being estimated as0.5. Therefore, S298.16=8.7 0.5
for Ir(c).
Spectroscopic data for Ir(g) (364) show that R In 10 should be added
to the Sackur equation in evaluating the entropy. The result is
S98.1e8=46.26 0.01.
IRON
Element.-The heat capacity of Fe(a) was measured by Duyckaerts
(133, 134) (1.50-200), Eucken and Werth (154) (160-2060), Gunther
(204) 320-950), Keesom and Kurrelmeyer (261) (10-210), Kelley (284)
(540-2960), Rodebush and Michalek (401) (720-1990), and Simon and
tSwain (443) (300-2200). The entropy obtained from these data is
S98.16= 6.49 0.03. The extrapolated portion is negligible, ca
4 X 104 below 10.
The entropy of Fe(g) may be obtained from spectroscopic data and
the Sackur equation. The lowest five energy levels, 6T4 5D, 5D2, 5D,
and 5D0, need be considered at 298.160. Moore (364) has listed the
term values for these levels as 0, 415.93, 704.00, 888.13, and 978.07
cm.-1, respectively. The quantum weights are 9, 7, 5, 3, and 1.
These states add 5.125 to the Sackur equation, so that S*9s.16=43.11
0.01 for Fe(g).
Ferrous Ion.-Latimer, Pitzer, and Smith (825) calculated S98.6-=
-25.9 1.0 for Fe++(aq.) from thermal data for the reaction Fe(c)+
2H+ (aq.)= Fe++(aq.) + H2 (g).
Ferric Ion.-Similarly, from thermal datafor the reaction Fe++ (aq.) +
H+(aq.) =Fe+++(aq.)+ 1/2H2(g), Latimer, Pitzer, and Smith (325)
found S298.16- 61 5 for Fe+++(aq.).
Ferrous Oxide.-Millar (362) (700-3020) measured the heat capacity
of a sample of "ferrous oxide" of 83 percent purity. The entropy
calculation gives S98.16-= 14.2 2.0, of which 1.34 is extrapolation
below 70.80
A value that probably is better was calculated by Kelley (273)
from equilibrium data for the reaction FeO (c) + H2(g) =Fe (a) H20 (g).
'The result is Ss8.16= 13.4 1.0. This value should be more certain
than the figure 12.6 calculated by Kielland (301) from data for the
reaction Fe203(1)-=2FeO(1)+ 1/202. More recently, Chipman and
Marshall (70) have obtained S29.16= 14.1 for FeO (or rather
wiistite) from a combination of their own and Emmett and Schultz's
(144) equilibrium data. The value S9s.1s= 13.41.0 is adopted
for FeO(c).
Ferric Oxide.-The heat capacity of Fe203(c) was measured by
Parks and Kelley (383) (880-2920). Two materials were employed,
specular hematite and the ignition product of ferrous oxalate. From
data for the specular hematite, S98s.18=21.50.5, of which 3.30 is
extrapolation below 89.20.
Magnetite.-Millar (362) (600-3000) and Parks and Kelley (383)
(900-2950) measured the heat dapacity of similar samples of Fe304
(magnetite) of 99 percent purity. From the combined data, S98s.5=
35.0+0.6. The extrapolation below 56.20 is 2.17.

55

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Kelley, K. K. Contributions to the Data on Theoretical Metallurgy: [Part] 11. Entropies of Inorganic Substances: Revision (1948) of Data and Methods of Calculation, report, 1950; Washington D.C.. (https://digital.library.unt.edu/ark:/67531/metadc12637/m1/59/ocr/: accessed May 26, 2019), University of North Texas Libraries, Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.

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