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

138
VIII Group 17 (halogen) compounds and complexes
Originally, the data for SnO(cr) were the calorimetric data measured by Lavut
et al. [1981LAV/TIM]. However as reviewed in Section VII.2.2.3, the enthalpy of
formation of SnO is chosen to be − (284.24 ± 0.76) kJ·mol –1 . The enthalpy of formation
of HF(aq) has been taken from the selected auxiliary data (Table IV-1). Therefore, the
value
f
ο
m
Δ H (SnF 2 , cr, 298.15 K) = − (699.9 ± 2.2) kJ·mol –1
is selected. This value differs vastly from the calculated/estimated value of − (677 ± 10)
kJ·mol –1 by Gurvich and Veyts [1991GUR/VEY].
Reaction
Table VIII-1: Thermochemical cycle used in [2001SOL/VLA].
r
ο
m
−Δ H /kJ·mol –1 Reference
1 SnF 2 (cr) + HF(aq) H[SnF 3 ](aq) 12.00 ± 0.30
2 SnO(cr) + 3 HF(aq) H[SnF 3 ](aq) + H 2 O(l) 67.20 ± 1.40
3 H 2 (g) + ½ O 2 (g) H 2 O(l) 285.83 ± 0.05 [1982GLU], [1989COX/WAG]
4 ½ H 2 (g) + ½ F 2 (g) HF(aq) 323.15 ± 0.72 NEA TDB auxiliary data
5 Sn(cr) + ½ O 2 (g) SnO(cr) 284.24 ± 0.76 This review
6 Sn(cr) + F 2 (g) SnF 2 (cr) 699.91 ± 2.17
Δ H (SnF ,cr) = Δ H =−Δ H +Δ H −Δ H + 2Δ H +Δ H
f 2 r 6 r 1 r 2 r 3 r 4 r 5
Thourey et al. [1983THO/PER] determined the standard enthalpies of
formation of SnF 2 (cr), PbF 2 (cr) and PbSnF 4 (cr) by alkaline hydrolysis and obtained a
value of − (736 ± 16) kJ·mol –1 for the enthalpy of formation of SnF 2 (cr). The error is
unacceptably high.
There are no other thermochemical data on this system. However, from
ο
solubility studies in the system SnF 2 -HF-H 2 O, ΔfG m
(SnF 2 , cr, 298.15 K) = − (639 ± 1)
kJ·mol –1 was estimated (see Section VIII.2.1.1).
VIII.1.1.2 Ternary fluorides
VIII.1.1.2.1 PbSnF 4 (cr)
The heat capacity was measured by adiabatic calorimetry at 10 to 352 K
[1988CAL/WEI] and by DSC at 270 to 650 K [1991CAL/WEI]. A number of previous
investigations [1978REA/LUC], [1979PAN/DEN], [1980PER/VIL] and
[1981CLA/LET] used DTA, DSC, XRD and dilatometry and claimed solid-solid
transitions at 353 (350), 533, 628 (623, 620) and 653 K. In some cases enthalpies of
transition and lattice parameters were reported. The heat-capacity measurements of
[1991CAL/WEI] are here taken as definitive, and were interpreted [1991CAL/WEI] as
establishing the following transitions as veridical:
CHEMICAL THERMODYNAMICS OF TIN, ISBN 978-92-64-99206-1, © OECD 2012