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

140
VIII Group 17 (halogen) compounds and complexes
VIII.1.1.2.3
SrSnF 4 (cr)
The heat capacity was measured by adiabatic calorimetry at 6 to 394 K
[1989CAL/SHA] and by DSC at 340 to 600 K [1991CAL/WEI]. The data were fitted to
the equation
ο 600K
p,m 290K
[ C ] (SrSnF 4 , cr, T )/J·K –1·mol –1 = − 172.407 + 2.29374 T/K – 0.00549 (T/K) 2
+ 4.67657 × 10 –6 (T/K) 3 .
The standard error of estimate is 3.8 J·K –1·mol –1 . The selected value is:
ο
C
p,m
(SnF 4 , cr, 298.15 K) = (147.4 ± 7.6) J·K –1·mol –1 .
From the heat-capacity data up to 298 K, the selected entropy is
[1989CAL/SHA]
ο
S m (SrSnF 4 , cr, 298.15 K) = (187.2 ± 0.3) J·K –1·mol –1 .
There is no reported value of standard enthalpy of formation for this
compound.
VIII.1.2 Solid chlorides
SnCl 2 (cr) is a white crystalline solid with a melting point of 520 K and a boiling point
of 896 K.
Tin(IV) chloride SnCl 4 is a colorless liquid and will be treated in
Section VIII.2.2.3.
VIII.1.2.1 SnCl 2 (cr)
There is a limited number of calorimetric measurements on the enthalpy of formation of
SnCl 2 (cr) [1882THO], [1941KAP], [1973VAS/VAS2] with a large spread in the results
(− 327 to − 353 kJ·mol –1 ). The range, however, narrows to within 5 kJ·mol –1 if we reject
the results from [1941KAP] being too disparate from any other. Vasil’ev et al.
[1973VAS/VAS2] determined the heats of solution of SnCl 2 in hydrochloric acid
solutions containing hydrogen peroxide. The method of synthesis of the samples assures
the purity and the reliability of the data. The authors used 1 M and 2 M HCl solutions at
w = 1.5 and 2.5% H 2 O 2 , and the heats of dissolution were closely similar. Their results
are reported in Table VIII-2. The weighted average of value and uncertainty are given
as − (327.86 ± 1.08) kJ·mol –1 in agreement with the value reported by
[1973VAS/VAS2] – (78.36 ± 0.26) kcal·mol –1 .
The enthalpy was also determined from potential measurements by Bugden
and Shelton [1970BUG/SHE] who used displacement cells of the type:
M | MCl n PbCl 2 AgCl | Ag.
CHEMICAL THERMODYNAMICS OF TIN, ISBN 978-92-64-99206-1, © OECD 2012