Chemical Thermodynamics of Tin - Volume 12 - OECD Nuclear ...

292
A Discussion of selected references
accounts for the bulk of this 0.15% (If the numerical values of w SnO , wHO
2 and w CO2
are
correct, then the undetermined rest, w (rest) = 0.22%, but this probably doesn’t change
the results significantly). There was a contamination w Si = 0.014%.
Figure A-16: Temperature dependence of log10
β
q
((A.27), q = 1, 2, 3) recalculated
from [1952VAN/RHO] (: log10 β
1
, : log10 β
2
, ◦: log10 β
3
).
2.0
1.8
Sn 2+ + qCl – SnCl 2–q
q
1.6
log 10
β q
1.4
1.2
1.0
0.8
0.0031 0.0032 0.0033 0.0034 0.0035 0.0036 0.0037
K/T
The energy equivalent of the calorimeter was determined with benzoic acid.
The unburned tin of Reaction (A.28) ranged from 1.02 to 4.11% of the total, and the
respective corrections were made in the heat measurement. Corrections for impurities of
the tin were applied. Combustion according to Reaction (A.29) was 100% complete,
and X-ray diffraction of the combustion product gave only lines corresponding to
tetragonal tin(IV) oxide. Corrections for the water, carbon dioxide and tin(IV) oxide
contents of the tin(II) oxide were made. In addition all measurements were corrected to
unit fugacity of oxygen, to constant pressure, and to 298.16 K.
The enthalpies of formation of tin(II) oxide and tin(IV) oxide were found to be
Δ H
ο
f m
ο
fHm
(SnO, tetr., 298.15 K) = − (285.98 ± 0.67) kJ·mol –1 and
Δ (SnO 2 , tetr., 298.15 K) = − (580.82 ± 0.33) kJ·mol –1 .
The possibility to recalculate these results is rather limited, because the authors
do not report to which measurements the different corrections for unburned tin have to
be assigned. It seemed, however, justified to use currently valid molar masses for tin
and tin(II) oxide. From the five determinations of the enthalpy of Reaction (A.29) it can
CHEMICAL THERMODYNAMICS OF TIN, ISBN 978-92-64-99206-1, © OECD 2012