Contributions to the Data on Theoretical Metallurgy: [Part] 11. Entropies of Inorganic Substances: Revision (1948) of Data and Methods of Calculation Page: 42
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42 CONTRIBUTIONS TO DATA ON THEORETICAL METALLURGY
Oxide.-Anderson (22) (560-3360) measured the heat capacity of
Cr203(c). His data yield Si.2=0.53 (extrapolation), S98.186-S8.2=
18.88 (measured), and S 98.1.= 19.4 0.3.
Carbides.-Kelley, Boericke, Moore, Huffman, and Bangert (295)
have reported low-temperature heat-capacity data from three chro-
mium carbides (Cr4C, 540-2950; Cr3C2, 530-2960; and Cr7C3, 540-2960).
The entropy values for Cr4C(c) are S0.12= 0.84 (extrapolation),
Ss98.1-S0.12= 24.46 (measured), and S298.16= 25.3 0.2.
For Cr3C2(c) there are obtained S50.12- 0.56 (extrapolation),
S98.as.-S50.12= 19.79 (measured), and S298.18= 20.35 0.10.
The corresponding values for Cr7C3(c) are S~0.12= 1.70 (extrapola-
tion), S2,8.16- S50.12-46.32 (measured), and S98s.1= 48.0 0.3.
Dichloride.-The heat capacity of CrCl2(c) was measured by Ander-
son (22) (430-2970). Recalculation of his data gives S98.16=27.7
0.7, of which 5.05 is extrapolation below 44.70. Doerner (131), from
equilibrium studies at high temperatures of the reaction CrC12(c)+
H2(g) = Cr (c) + 2HCl(g), obtained S9s.18-= 29.7. More recently, Maier
(343) has recalculated Doerner's data and obtained S2,98.1=27.3.
The value from the heat-capacity data, S98.16= 27.7 - 0.7 is adopted
for CrC12 (c).
Trichloride.-Anderson (22) (540-2970) and Trapeznikova, Shub-
nikov, and Miljutin (492) (120-1300) have measured the heat capacity
of CrCl3(c). Unfortunately, the two sets of data are in bad dis-
agreement over their common temperature range. As data of the
latter authors for other substances also are in disagreement with values
that are considered good, reliance must be placed largely on the data
of Anderson. This creates a difficult situation, as Trapeznikova and
his coworkers found an anomalous region just below 200.
Anderson's data alone give S99s.18=27.3, of which 3.19 is extrapola-
tion below 56.20. If allowance is made for a heat-capacity maximum
below 200, by constructing a curve resembling that of Trapeznikova
and his coworkers, then about 1.3 must be added to both the extra-
polated portion and the entropy at 298.160, making S298,18=28.6.
However, the procedure that will be followed here is to accept the
value from Anderson's measurements without this allowance and add
R In 4=2.76, corresponding to the splitting of the lowest energy level
of Cr+++, which is designated 4F312 by Bowen (52). This procedure
leads to S298.18=30.0 1.5, in which the large allowance for error
Doerner (131), from rather meager indirect equilibrium data for
the reaction 2CrCl3(c)= 2CrCl12(c) +Cl2 (g), computed S298.16= 31.0
for CrC13(c). However, Maier's (343) recalculations indicate that
values in the range 28.2 to 31.0 may be obtained from these data.
The value adopted for CrCl3(c) is S298.16=030.01.5.
Chromate Ion.-Latimer, Pitzer, and Smith (325) obtained S0298.16=
10.5 1.0 for CrO4--(aq.) from thermal data for the reaction
Ag2CrO4(c)= 2Ag+(aq.) + CrO4-- (aq.).
Element.-The heat capacity of Co(c) was measured by Aoyama
and Kanda (29) (790-2740), Duyckaerts (135) (20-180), and Simon
and Ruhemann (441) (710-720). The data lead to S98.1= 6.86 +t0.10,
of which only ca. 8 X 10-4 is extrapolation below 20
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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/m1/46/: accessed April 19, 2019), University of North Texas Libraries, Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.