Contributions to the Data on Theoretical Metallurgy: [Part] 11. Entropies of Inorganic Substances: Revision (1948) of Data and Methods of Calculation Page: 58
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58 CONTRIBUTIONS TO DATA ON THEORETICAL METALLURGY
Lead Ion.-From thermal data for the reaction PbC12(c)=Pb++
(aq.) +2Cl-(aq.), Latimer, Pitzer, and Smith (325) obtained S298.16=
3.90.9 for Pb++(aq.).
Oxides.-The heat capacity of PbO(c), presumably the yellow
variety, was measured by Nernst and Schwers (377) (210-930). There
is obtained S29.16- 16.6 + 0.5, of which 0.55 is extrapolation below 200.
The entropy may be calculated independently from the cell measure-
ments of Fried (163) for the reaction PbO(c)+H2=Pblc) +H20(1).
From the e. m. f. measurements and their temperature coefficient,
the value ASs98.16= - 16.80 is obtained, which in turn leads to SO8.1=
17.8 1.0 for PbO. The third-law value, S298.16= 16.6 05, is adopted.
From molecular constants (212), I=91.2X 10-40 and w=718, there
are computed SI+,, 298.16= 57.06, S , 298.16=0.29, and S298s.1= 57.340.10
for PbO (g). A rough check on this value is afforded by the heat and
free energy of sublimation (269), which correspond to AS8s.16= 39.3.
Adding the entropy of the solid gives S29s.16= 55.9 for PbO(g), which
merits no weight in comparison with the value from molecular
Millar (361) (690-2980) measured the heat capacity of PbO2(c).
There is computed S298.16= 18.3 0.5, of which 3.50 is extrapolation
Millar (361) (710-2390) also measured the heat capacity of Pb304(c).
The calculated results are Sk0.s= 12.67 (extrapolation), Ss98.16-So.s=
37.83 (measured), and S298.1=50.51.6.
Bromides.-The heat capacity of PbBr2(c) was measured by
Latimer and Hoenshel (321) (180-2970). The data yield S298.16=38.6
0.5, of which 1.64 is extrapolation below 17.80. Cann and Sumner (68)
have obtained AS s.18= -12.60 for the reaction Pb(c)+2AgBr(c)-=
PbBr2(c)+2Ag(c). Corresponding to this result, S98s.18= 33.7 may
be calculated for PbBr2(c), which disagrees with the third-law value
and also appears out of line with the entropies of PbC12(c) and PbI2(c).
From values of I=603X10-40 and ow=207, and quantum weight of
2 for the lowest energy level, there are computed St+,, 298.16= 61.56,
S~, 298.1=2.24, S :, 29s.18= 1.38, and S.98.18=65.20.5 for PbBr(g).
Carbonate.-The heat capacity of PbCO3 (cerussite) was measured
by Anderson (16) (530-2940). The data give S58.2= 6.45 (extrapola-
tion), Ss98.18- S8.2= 24.82 (measured), and S298s.18= 31.3 0.8.
Basic Carbonate.-From dissociation pressure and thermal data, the
value S98s.18=48.5 1.5 was obtained for PbO.PbCO3(c) by Kelley and
Chlorides.-The heat capacity of PbC12(c) was measured by Nernst
(373) (150-2060). There is calculated S2s.16=34.01.0, with an
extrapolation of 0.91 below 15.80.
Gerke's (169) cell measurements permit two independent calcula-
tions. He gave AS29s.16= -8.6 for the reaction Pb(c) +2AgCl(c)=
PbC12(c) +2Ag(c) and AS8.18= =6.7 for the reaction Pb(c)+2HgCl(c)
=PbCl2(c)+2 Hg(1). The corresponding calculated entropies of
PbC12(c) are S9s8.1= 32.5 .05 and S98.18= 32.2 1.0. The value
S 2s8.16=32.50.5 is adopted.
From molecular-constant data (467), I= 282 X 10-40 and w=303, and
quantum weight of 2 for the lowest energy level, there are obtained
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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/m1/62/: accessed April 23, 2019), University of North Texas Libraries, Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.