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

142
VIII Group 17 (halogen) compounds and complexes
The heat capacity of SnCl 2 (cr) in the temperature range of 5 to 305 K was
measured by Paukov et al. [1979PAU/STE]. The measured values for the sample of
high purity (w(SnCl 2 ) = 99.5%) in the PbCl 2 -type rhombic phase are shown in
Appendix A. They estimated the accuracy of the measurements as 0.2% at T > 25 K and
about 0.5% at T < 25 K. The heat-capacity data of [1979PAU/STE] may be treated by
two alternate methods as discussed below. In either case, we may separate the data in
two sets; the lowest temperature data below approximately 9 K can be fitted with the
ο
p,m
Debye’s T 3 law function C = a·T 3 . In the SnCl 2 (cr) case this law is valid up to
≈ 9 K (Figure VIII-1). Thus a = 0.003365 J·K –4·mol –1 ο
can be obtained from C p,m data
measured at the 6 lowest temperatures
H
ο
m
(5 K) −
ο
S
m
(5 K) =
5K o
∫ C
0 K
p, mdT
= a·5 4 /4 = 0.5258 J·mol –1
5K
o
∫ Cp, m T T = a·5 3 /3 = 0.1402 J·K –1·mol –1 .
ο
H m (0 K) =
0 K ( / )d
Figure VIII-1: Low temperature heat capacity of SnCl 2 (cr). Experimental data of
Paukov et al. [1979PAU/STE] with a linear fit (temperature range 5 to 9 K).
5
4
C° p, m
/ (J·K –1·mol –1 )
3
2
1
0
0 500 1000 1500 2000
(T / K) 3
For the data between 9 and 304 K, we have the choice of finding a suitable
polynomial equation as used in calculation programs such as Chemsage
[1998ERI/HAC] or use a spline function (see below). The polynomial equation is:
CHEMICAL THERMODYNAMICS OF TIN, ISBN 978-92-64-99206-1, © OECD 2012