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

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VIII Group 17 (halogen) compounds and complexes
VIII.1.4 Solid iodides
VIII.1.4.1 Introduction
SnI 2 is a red or red-orange colored crystalline solid (monoclinic) with a melting point of
589 K, a boiling point of 993 K [1984GRE/EAR].
SnI 4 (cr) is a brown or yellow-brown crystalline solid (cubic) with a melting
point of 417 K, a boiling point of 621 K [1984GRE/EAR].
VIII.1.4.2 SnI 2 (cr)
Mikler and Janitsch [1975MIK/JAN2] measured the heat of the reaction SnI 2 (s) + I 2 (s)
+ 4045CS 2 (l) [SnI 4 ; 4045CS 2 ](sln) to be − (41.12 ± 0.55) kJ·mol –1 by isoperibol
solution calorimetry. The heat of formation of SnI 2 (cr) was calculated by using the
literature data for SnI 4 previously measured by Mikler [1973MIK]. The enthalpy of
formation at 298 K for SnI 2 (cr) is determined to be − (153.9 ± 1.40) kJ·mol –1 .
Stenin et al. [1975STE/KOK] determined the standard enthalpy of formation of
SnI 2 (cr) by direct calorimetry in the range 332 to 593 K (20 points). The heats of
dissolution of Sn(cr), SnBr 2 (cr), SnBr 4 (cr), Br 2 (l) in (CCl 4 + Br 2 + SnBr 4 ) and the heats
of dissolution of Sn(cr), SnI 2 (cr), SnI 4 (cr), I 2 (cr) in (CCl 4 + I 2 + SnI 4 ) were measured by
a calorimetric method. A high purity sample was used for SnI 2 (monoclinic) and the
ο
enthalpy of formation at 298.15 K is determined as Δ fHm(SnI 2 , cr, 298.15 K) =
− (152.1 ± 2.0) kJ·mol –1 .
A second calorimetric measurement following the same method is by Mikler
ο
[1973MIK] which resulted in Δ H (SnI 2 , cr, 298.15 K) = − (153.9 ± 1.4) kJ·mol –1 .
f
m
We accept the data based on [1977STE/KOK] and [1975MIK/JAN2]. Thus the
selected value of the enthalpy of formation of SnI 2 (cr) is:
f
ο
m
Δ H (SnI 2 , cr, 298.15 K) = − (153.3 ± 2.3) kJ·mol –1 .
A third calorimetric measurement by Cartwright and Woolf (1976) was not
considered because of the missing experimental details.
Anisimov et al. [1974ANI/ZHA] determined the heat capacity of SnI 2 (cr) (11.7
to 312.7 K) on a sample of high purity with an accuracy of the measurements estimated
as lying within 0.1 to 0.2% (see Appendix A). Their data were fitted by this review to
ο 312.7 K
the equation: [ C ] (SnI 2 , cr, T )/J·K –1·mol –1 = (76.62 + 0.0228 T/K − 1459 /(T/K)
p,m 11.7 K
ο
p,m
+ 8107 /(T/K) 2 ), resulting in C (SnI 2 , cr, 298.15 K) = (78.62 ± 0.16) J·K –1·mol –1 . The
equation is given only if any limited extrapolation is required. For the standard state
data, this review selects:
ο
–1
C p,m (SnI 2 , cr, 298.15 K) = (78.45 ± 0.16) J·K
–1·mol
CHEMICAL THERMODYNAMICS OF TIN, ISBN 978-92-64-99206-1, © OECD 2012