4
6
L. Wang et al. / Thermochimica Acta 490 (2009) 43–46
Table 4
The standard molar enthalpies of formation of the rare earth
oxide, H O(l) and CO (g) were obtained from Refs. [19,20] were
The standard molar enthalpies of formation of the rare earth oxide, H2O(l) and
CO2(g).
2
2
listed in Table 4. The results of the calculations are also listed in
Table 3.
ꢀfHꢁ (kJ mol
−1
)
Rare earth oxide
ꢀfHꢁ (kJ mol
−1
)
Rare earth oxide
m
m
ꢁ
ꢁ
La2O3(s)
Pr2O3(s)
Sm2O3(s)
Gd2O3(s)
Dy2O3(s)
Er2O3(s)
Yb2O3(s)
CO2(g)
−1791.6 ± 2.0
−1809.9 ± 3.0
−1826.8 ± 4.8
−1819.7 ± 3.6
−1863.4 ± 5.0
−1900.1 ± 6.5
−1814.5 ± 6.0
−393.51 ± 1.3
CeO2 (s)
−1090.4 ± 1.0
−1806.9 ± 3.0
−1662.5 ± 6.0
−1865.2 ± 6.0
−1883.3 ± 8.2
−1889.3 ± 5.7
−1877.0 ± 7.7
−285.830 ± 4.0
In Fig. 3, we have given that ꢀcHm, ꢀfHm of the above com-
plexes are plotted against the atomic numbers of the elements in
the lanthanide series. The curve shows the “tetrad effect” of rare
earth, suggesting that a certain amount of covalence is present in
Nd2O3 (s)
Eu2O3 (s)
Tb2O3 (s)
Ho2O3 (s)
Tm2O3 (s)
Lu2O3 (s)
H2O (l)
3+
the chemical bonds between RE and ligand, which is caused by
2
6
the incomplete shield of 5s 5p orbital to 4f electrons. The exper-
imental result is in agreement with the Nephelauxetic effect of 4f
electrons of rare earth.
On the basis of Fig. 3, the corresponding standard enthalpy
of combustion and the standard enthalpy of formation of
−
1
Pm(Hbtec)·3H O could be estimated as being −3150 kJ mol and
2
−
1
−
2910 kJ mol , respectively.
Acknowledgements
The investigation received financial assistance from Shaanxi
Province of China (Grant No. 2007K02-10), Education Committee
of Shaanxi Province (Grant No. 05JC31).
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ꢁ
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m
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f
m
2
3
f
m
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2
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10
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8
2
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[
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(3)
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ꢁ
ꢁ
ꢁ
ꢀfH (s) = ꢀ H (CeO , s) + 10ꢀ H (CO , g)
m
f
m
2
f
m
2
[
9
2
ꢁ
m
ꢁ
m
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[
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ꢀ H (H O, l) − ꢀcH (Ce(C H O ) · 3H O, s) (4)
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2
10
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2
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1
2
ꢁ
m
ꢁ
m
ꢁ
m
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f
2
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7
2
ꢁ
m
ꢁ
m
+
ꢀ H (H O, l) − ꢀcH (RE(C H O ) · 2H O, s)
f
2
10
3
8
2
(
RE = Sm–Gd)
(5)