Contributions to the Data on Theoretical Metallurgy: [Part] 11. Entropies of Inorganic Substances: Revision (1948) of Data and Methods of Calculation Page: 29
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ENTROPIES OF INORGANIC SUBSTANCES AT 298.16 0K.
in the entropy calculation, as the data of the latter are very erratic.
Weber (498) has given the melting point as 265.90 and Regnault (396),
the heat of fusion as 2,580 cal. per mole. A mean heat capacity of
Br2(), C,=17.0, was measured near room temperature by Andrews
The data of Latimer and Hoenshel lead to the values S1 4.1=0.68
(extrapolation) and S265.9-S104.1=24.32 (crystals), making the value
for Br2(c) at the melting point S'65.9= 25.00. The entropy of fusion
is AS 265.809=9.70, and the entropy increment in heating the liquid
from 265.90 to 298.160 is 1.94. Therefore, S09s.16=36.6==0.5.
Woitinek (503) has obtained AS~,s.16,= -3.00 for the reaction Ag(c)
+ 1/2Br2(1)=AgBr(c). Employing the value S9,s.16= 10.20 0.05 for
Ag(c) and S298.16=25.600.1 for AgBr(c), there is obtained S'98.16-
36.8= 0.4 for Br2(1), in agreement with the result from heat-capacity
The mean value, S298.1=36.7 0.4 is adopted.
Brown (66) has computed the following values for Br2(g) from
spectroscopic data: S298.16= 58.56 for Br?,79, So9.1= 60.01 for
Br,9's1, and S2S9.16=58.70 for Br 1,81. For the usual isotopic mixture
he obtained S298.16= 58.63. The latter value was checked by Gordon
and Barnes (201) who obtained S98s.16= 58.67. Using available
molecular-constant data (212), 1=342.5X10-40 and w=322, there is
obtained S+r,298.16= 57.31 and SV298.16-=1.30, making S098.16= 58.61.
The value given by Brown, S29.16-58.63, is adopted. The error
should not exceed 0.03 unit.
The spectroscopic data for monatomic, Br (g), gas show that at
298.160 all but a negligible portion of the molecules are in the lowest
energy state, which is a 2P3/2 state with quantum weight 4. The
Sackur equation with R In 4 added yields S9s.1e=41.81 +0.01 for
Bromide Ion.-Latimer, Pitzer, and Smith (325) have obtained the
entropy of Br- (aq.) from data for three reactions, AgBr(c) + Cl- (aq.)=
AgCl(c) + Br- (aq.), AgBr(c) + lHl(g) = H+(aq.) +Br- (aq.) +Ag(c),
and 2 Br2(l)*Cl-(aq.)=2 C12(g)+Br-(aq.). The results are,
respectively, 19.80.2, 19.60.3, and 19.50.4. Their selected
result, S9s.16=--19.7 0.2, is adopted here.
Bromate Ion.-The entropy of BrO3-(aq.) has been obtained by
Latimer, Pitzer, and Smith (325) from data for the reactions KBrO3
(c) =K+(aq.) +BrO3-(aq.) and Ba(BrO3)2.H20 (c)=Ba++(aq.) +2BrO3-
(aq.) + H20(1). The values are, respectively, 38.7 1 and 38.1 +2.
Their selection, S2,s.16=38.51.0, is adopted.
Chloride.-From thermal measurements in CC14 solutions Blair and
Yost (45) have obtained S29s.16= 57.1 for BrCl(g). The later paper
of Beeson and Yost (41) gives AS21,s.16=2.83 for the reaction Br2(g)+
C12(g)= 2BrC1 (g). This result and the entropies of Br2(g) and
C12(g) lead to S9s.16= 57.4 for BrCl(g). Available molecular-con-
stant data (212) give S+r,298.16- 56.47 and S.298.16=0.89, making
298.16-= 57.360.10. The last figure is adopted.
Fluoride.-The entropy of BrF(g) may be calculated from the rela-
tionship, Ss98.16 (BrF (g))- S 98s.1(Br2(g)) Ss98.16 (F2(g)) +Rln 2.
The result is S98.16 = 54.98 0.10.
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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/m1/33/: accessed April 21, 2019), University of North Texas Libraries, Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.