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

VII.2 Solid tin oxides and hydroxides 119
Hirayama [1964HIR] stated that the entropy of this compound is reported
(source unknown) to be (56.5 ± 1.3) J·K –1·mol –1 ο
. If we use the value of (Sn, cr,
white, 298.15 K) = (51.18 ± 0.08) J·mol –1·K S m
–1 selected in this review, and the CODATA
value for oxygen as (205.152 ± 0.005) J·K –1·mol –1 , the calculated entropy of formation
is − 97.26 J·mol –1·K –1 ο
and the resulting Δ is − 257.00 kJ·mol –1 fGm
. Humphrey and
O’Brien’s value for the enthalpy of formation (− 286.00 kJ·mol –1 ) differs considerably
from the value measured by Lavut et al. [1981LAV/TIM] who determined the enthalpy
ο
of formation of SnO(cr) as: Δ fHm(SnO, tetragonal, 298.15 K) = − (280.71 ± 0.21)
kJ·mol –1 . They used a well characterised sample in combustion calorimetry, the same
method as used in [1953HUM/OBR]. The enthalpy of SnO(cr) differs from that
reported in [1953HUM/OBR] significantly by almost 2%. The large discrepancy
between the combustion calorimetric results cannot be resolved by looking at only these
two sets of data. Arguments favouring the data by Lavut et al. [1981LAV/TIM] are
based on a) high purity tin specimens, b) a reliable method of determining the reaction
completeness, and c) a higher degree of combustion of tin. Lavut et al. also question the
presence of water in gas form in the bomb which was not accounted for by Humphrey
and O’Brien.
A quite thorough review of the available data ([1978COX], [1979GLU/MED],
[1982WAG/EVA], [1982PAN]) was provided by Lamoreaux and Hildenbrand
ο
[1987LAM/HIL]. Their recommended values for Δ fHm(SnO, cr, 298.15 K) and
ο
S (SnO, cr, 298.15 K) are − (280.681 ± 0.166) kJ·mol –1 m
and (57.167 ± 0.291)
J·K –1·mol –1 respectively. The value of the enthalpy of formation of SnO(cr) is found to
be consistent with the evaluation by [1979GLU/MED], [1978COX] and [1982PAN] but
different from [1982WAG/EVA]. The entropy value is as in [1979GLU/MED] but
different from others.
Solov’ev et al. [2001SOL/VLA] measured the enthalpies of reactions of
SnO(cr) and SnF 2 (cr) with hydrofluoric acid in an isothermic-shell calorimeter. They
used the reaction:
SnO(cr) + 3 HF(l) H[SnF 3 ](l) +H 2 O(l)
and obtained a value of − (67.2 ± 1.4) kJ·mol –1 for the enthalpy of reaction but did not
ο
complete the thermochemical cycle to get the data for Δ H (SnO, cr, 298.15 K).
The data of [1981LAV/TIM] and two critical reviews [1987LAM/HIL] and
[1991GUR/VEY] support the higher value of enthalpy, while the dataset of Humphrey
and O'Brien [1953HUM/OBR] using the same calorimetric method favours the lower
value. There are two other determinations of enthalpy, one by Maier [1929MAI] who
measured the potentials of galvanic cells and obtained − (285.4 ± 4.0) kJ·mol –1 and the
second by Garrett and Heiks [1941GAR/HEI] who used solubility measurements and
obtained − (283.9 ± 3.0) kJ·mol –1 . It will be shown in Section VII.2.2.4 that the data of
ο
[1981LAV/TIM] cannot be taken into account for the evaluation of ΔfH m(SnO, cr,
298.15 K).
f
m
CHEMICAL THERMODYNAMICS OF TIN, ISBN 978-92-64-99206-1, © OECD 2012