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

VIII.1 Halide compounds
157
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S m (SnI 2 , cr, 298.15 K) = (167.8 ± 1.0) J·K –1·mol –1 .
The Gibbs energy of formation of SnI 2 (cr) is calculated to be:
Δ G (SnI 2 , cr, 298.15 K) = − (153.44 ± 2.32) kJ·mol –1 .
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m
Gardner and Preston [1991GAR/PRE] used DSC to determine the heat capacity
of the halides. The method results in data which are estimated to have an accuracy of
± 2% between 300 and 1000 K. Such data were fitted to an equation (a + b T ) with the
coefficients a = (67.23 ± 0.22) and b = (0.03528 ± 0.00047) over the temperature range
of 350 to 590 K. The extrapolated value at 298.15 is 77.7 J·K –1·mol –1 , similar to the
datum selected above.
VIII.1.4.3 SnI 4 (cr)
Stenin et al. [1975STE/KOK] measured the heats of dissolution of Sn(cr), SnI 2 (cr),
SnI 4 (cr), I 2 (cr) in (CCl 4 + I 2 + SnI 4 ) by the calorimetric method and determined the
standard enthalpy of formation in the range 330 to 414 K (20 points) for the compound
SnI 4 (cr); the uncertainty in the enthalpy measurements was estimated as 0.6% at 330 to
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370 K and 0.3% at T > 370 K. The enthalpy at 298.15 K is determined as Δ fHm(SnI 4 ,
cr, 298.15 K) = − (206.1 ± 2.0) kJ·mol –1 .
Mikler [1973MIK] measured the enthalpy change at 298.15 K for the reactions
Sn(cr) + 2 I 2 (cr) +CS 2 (l) SnI 4 (CS 2 solution)
(VIII.7)
and SnI 4 (cr) + CS 2 (l) SnI 4 (CS 2 solution) (VIII.8)
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with Δ rHm(VIII.7) = − (195.39 ± 1.26) kJ·mol –1 and Δ rHm(VIII.8) = (13.39 ± 0.42)
kJ·mol –1 ο
, respectively. This results in Δ fHm(SnI 4 , cr, 298.15 K) = − (208.8 ± 1.3)
kJ·mol –1 .
The selected enthalpy of formation of SnI 4 (cr) must be determined by the two
calorimetric data that are found to be consistent. Both experiments involve the
dissolution reactions in CS 2 . Taking the weighted mean of the two values and
reassigning uncertainties by multiplying both σ by 2 yields:
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m
Δ H (SnI 4 , cr, 298.15 K) = − (208.0 ± 2.2) kJ·mol –1 .
A third calorimetric measurement by Cartwright and Woolf [1976CAR/WOO]
was not considered because of the missing experimental details.
Anisimov et al. [1974ANI/STE] determined the heat capacity of cubic SnI 4 in
the temperature range of 11.5 to 308 K on a sample of high purity with an accuracy of
the measurements estimated as lying within 0.1 to 0.2%. The values are reported in
ο 308K
Appendix A. The data were fitted by this review to the equation: [ C p,m ] 11.5K (SnI 4 , cr,
T )/J·K –1·mol –1 = 121.2 + 6.190 × 10 –2 T/K − 2113/(T/K) + 10731/(T/K) 2 for limited
extrapolation.
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CHEMICAL THERMODYNAMICS OF TIN, ISBN 978-92-64-99206-1, © OECD 2012