A calorimetric study of germanium dibromide

Article abstract of DOI:10.1134/S0036024406120077

The temperature dependence of the heat capacity of germanium dibromide was studied over the temperature range 8.3-314 K by adiabatic calorimetry. The enthalpy of formation of solid germanium dibromide was determined by solution calorimetry. Scanning calorimetry was used to obtain the thermodynamic characteristics of fusion of GeBr₂. The thermodynamic characteristics of the Ge-Br system studied by us earlier were used to consistently calculate the consistent standard enthalpies of formation and absolute entropies of germanium bromides in the solid, liquid, and gaseous states. Nauka/Interperiodica 2006.

Full text of DOI:10.1134/S0036024406120077

ISSN 0036-0244, Russian Journal of Physical Chemistry, 2006, Vol. 80, No. 12, pp. 1911–1914. © Pleiades Publishing, Inc., 2006.
Original Russian Text © L.N. Zelenina, T.P. Chusova, Yu.G. Stenin, G.A. Berezovskii, 2006, published in Zhurnal Fizicheskoi Khimii, 2006, Vol. 80, No. 12, pp. 2148–2152.
CHEMICAL THERMODYNAMICS
AND THERMOCHEMISTRY
A Calorimetric Study of Germanium Dibromide
L. N. Zelenina, T. P. Chusova, Yu. G. Stenin, and G. A. Berezovskii
Nikolaev Institute of Inorganic Chemistry, Siberian Division, Russian Academy of Sciences,
pr. Akademika Lavrent’eva 3, Novosibirsk, 630090 Russia
E-mail: zelenina@che.nsk.su
Received November 25, 2005
Abstract—The temperature dependence of the heat capacity of germanium dibromide was studied over the
temperature range 8.3–314 K by adiabatic calorimetry. The enthalpy of formation of solid germanium dibro-
mide was determined by solution calorimetry. Scanning calorimetry was used to obtain the thermodynamic
characteristics of fusion of GeBr . The thermodynamic characteristics of the Ge–Br system studied by us earlier
2
were used to consistently calculate the consistent standard enthalpies of formation and absolute entropies of
germanium bromides in the solid, liquid, and gaseous states.
DOI: 10.1134/S0036024406120077
INTRODUCTION
the other impurities (23 elements) were at the level of or
–2
–6
below their detection limits (10 –10 wt %). The dif-
fractograms of the samples only contained reflections
characteristic of germanium dibromide [3]. The above
analytic data allow us to claim that our physicochemi-
cal measurements were performed for single-phase ger-
manium dibromide with the total content of impurities
lower than 0.1 wt %.
Germanium halides are currently the main initial
material for the preparation of high-purity germanium
or compounds based on it. Reliable thermodynamic
data are necessary for selecting process schemes and
optimizing these processes. In [1], we reported such
data for the Ge–I system. The purpose of this work was
to obtain consistent thermodynamic information about
the properties of germanium bromides.
The samples were transferred into calorimetric
ampules and weighing bottles for analyses in a dry box
filled with argon; phosphorus pentoxide was used as the
drying agent.
EXPERIMENTAL
The temperature dependence of the isobaric heat
Germanium dibromide was synthesized according
to the procedure suggested in [2]. The initial substances
were GPZ os. ch. (special purity) germanium single
crystals (the concentration of residual impurities 2 ×
capacity of GeBr was measured by adiabatic vacuum
2
calorimetry; the characteristics of the unit and proce-
dure for measurements were described in [4]. The cal-
orimeter was calibrated by measuring the heat capacity
of benzoic acid. The results showed that the error in
heat capacity measurements was 1% at 5–50 K and
–12
3
10
at./cm ) and bromine of kh. ch. (chemically pure)
grade (the content of the major component 99.99%)
purified additionally by vacuum sublimation. The car-
rier gas was TU 6-21-12-79 argon (no less than
0
.2% at 50–300 K.
Scanning calorimetry was used to determine the
9
9.998% argon and no more than 0.0003% moisture)
thermodynamic characteristics of compound fusion
additionally purified from water by concentrated sulfu-
(
Tfus and ∆ H°). Calorimetric measurements were per-
ric acid. The reaction gave a mixture of GeBr , Ge, and
GeBr , which was dissolved in a water-free diethyl
fus
2
formed on a Setaram DSC 111 scanning calorimeter at
heating rates of 1–3 K/min. Sample weights were of
4
ether preliminarily dried by distillation over sodium
metal. The solution was prepared in a dry box filled
with argon and filtered from germanium particles.
Ether and germanium tetrabromide were removed by
heating the transparent solution obtained on a water
bath in a vacuum. The remaining dry residue was pale
2
0–30 mg. During measurements, the substance was in
evacuated glass ampules. The limiting error in heat
effects was 0.9% (estimated in calibration against refer-
ence substances, KNO and Sn).
3
Solution calorimetry was used to determine the
yellow GeBr crystals. The product was identified by standard enthalpy of formation of germanium dibro-
2
chemical, x-ray powder, and spectral analyses. Accord- mide. The heats of solution were measured in a liquid
ing to the chemical analysis data, it contained (wt %) isothermic-shell calorimeter [5]. The reliability of the
Ge, 31.0 ± 0.5 and Br, 68.37 ± 0.45; calculated for calorimetric system was checked by measuring the heat
GeBr (wt %): Ge, 31.24 and Br, 68.76. According to of solution of KCl in water. The mean enthalpy of solu-
2
the atomic absorption spectrophotometry data, the sam- tion was in agreement with the value accepted as the
–
3
ple contained 6 × 10 wt % silicon, and the contents of international standard (17.524 ± 0.007 kJ/mol) [6] to
1
911

1
912
ZELENINA et al.
Table 1. Experimental heat capacities of GeBr (s) (C° , J/(mol K))
2
p
T, K
C°
T, K
C°
T, K
C°
T, K
C°
p
p
p
p
Series 2
217.92
222.34
226.72
231.06
240.55
245.30
250.00
254.66
259.28
263.88
268.44
272.97
277.49
281.97
82.38
83.41
84.13
84.87
86.79
86.41
87.92
88.45
89.13
89.65
90.66
91.04
90.23
90.97
108.04
112.81
117.41
121.86
126.61
65.05
66.10
67.23
68.58
69.51
12.40
14.11
15.05
16.24
17.70
19.43
21.14
22.98
25.40
28.13
31.11
34.45
38.36
43.71
49.83
55.76
61.85
68.39
75.35
6.86
8.93
1
1
1
1
1
1
1
1
1
1
1
35.01
39.50
44.17
49.00
53.76
58.42
63.26
68.27
73.20
78.06
82.85
70.08
71.21
72.32
72.23
73.31
74.25
75.11
76.52
77.87
77.53
77.55
9.93
11.25
12.84
14.72
16.75
18.78
21.34
24.03
26.90
29.90
33.08
37.07
41.01
44.75
47.88
51.03
54.10
Series 4
Series 5
304.40
309.97
314.70
93.54
94.96
96.65
275.36
279.81
285.06
295.51
290.30
91.91
93.59
93.47
97.10
95.91
Series 1
1
1
1
1
2
2
2
86.25
90.51
95.19
99.83
04.41
08.95
13.46
77.50
78.35
78.92
79.39
80.43
81.19
81.52
Series 3
83.82
88.18
92.88
97.84
103.07
56.79
59.11
60.64
61.18
63.36
Series 6
8.32
8.97
2.78
3.36
4.01
5.13
9.77
11.00
within 0.1%. The heats of solution were measured at C (T) curve were 1.5, 0.3, and 0.15% over the temper-
p
3
01 K, because the temperature of fusion of GeBr4 ature ranges 8–16, 16–35, and 35–275 K, respectively.
equaled 299.35 K.
The accuracy of the calculated values was estimated
with the inclusion of both errors in calorimeter calibra-
tion against benzoic acid and the spread of experimen-
tal heat capacity values over the whole temperature
interval.
The solvent used was distilled benzene bromide
6 5
(
C H Br) of ch. (pure) grade. The enthalpy of formation
of GeBr was calculated from the heats of the calori-
2
metric reactions
The smoothed C (T) dependence was used to calcu-
late the absolute entropy S°, the enthalpy of heating
p
Br (l) + sln I
sln II + ∆H1,
(1)
(2)
(3)
2
GeBr (s)+ sln II
sln III + ∆H2,
sln III + ∆H3,
2
H° – H° , and the reduced Gibbs energy Φ° = S° – [H° –
T
0
T
GeBr (l) + sln I
4
H° ]/T. Their values at the selected temperatures are
0
where sln I = 21.5Br + 4.2GeBr + 2025C H Br.
listed in Table 2.
2
4
6
5
Scanning calorimeter measurements were per-
formed over the temperature range 273–500 K. To
within the sensitivity of the method, the substance stud-
ied was a pure phase. The only phase transition
observed over the temperature range of measurements
was fusion.
The concentrations of the calorimetric solutions
used ensured a fairly high rate of reactions on the one
hand (Br and GeBr were dissolved in 5–10 min and
2
4
GeBr in 20–30 min) and the independence of the heats
2
of reactions (1)–(3) from changes in the concentrations
of the substances to be dissolved.
The thermodynamic characteristics of fusion
obtained from the differential scanning calorimeter
RESULTS AND DISCUSSION
data were ∆ H°(GeBr ) = 11.6 ± 0.1 kJ/mol, T =
fus
2
fus
4
09.15 ± 0.5 K, and ∆ S° = 28.3 ± 0.5 J/(mol K).
The heat capacity of germanium dibromide was
measured over the temperature range 8.3–314 K. The
fus
Solution calorimetry measurements for bromine and
weight of the sample was 4.890 g, the molecular weight germanium bromides gave the following enthalpies of
of GeBr being 232.418. The results of 73 calorimetric
2
reactions (1)–(3) (kJ/mol): ∆ H° = –4.25 ± 0.49,
r1 301
experiments are presented in Table 1. The mean devi-
ations of the experimental values from the smoothed
∆r2 H° = –185.12 ± 1.40, and ∆ H° = 0.98 ± 0.025.
301
r3 301
RUSSIAN JOURNAL OF PHYSICAL CHEMISTRY Vol. 80 No. 12 2006

A CALORIMETRIC STUDY OF GERMANIUM DIBROMIDE
1913
The errors specified correspond to a 95% confidence Table 2. Main thermodynamic functions of GeBr (s)
2
(
C° (T), S°(T), and Φ°(T) in J/(mol K) and H°(T) – H°(0) in
level. For each reaction, five measurements were per-
formed, and the weights of solute samples were (g)
p
J/mol)
0
.09–0.16 for Br , 0.15–0.27 for GeBr , and 0.22–0.37
2 2
H°(T)
T, K
C° (T)
S°(T)
Φ°(T)
for GeBr . The mean cooling constant value in our
p
4
– H°(0)
–
4
–1
experiments was 41 × 10 s . The correction for heat
exchange calculated by the Regnault–Pfaundler
method was no larger than 7% of the overall tempera-
ture rise on average.
5
.00
(0.702)
4.14
(0.887)
11.9
(0.236)
1.63
(0.059)
0.438
1.24
10.00
1
5.00
9.27
45.1
4.25
The ∆ H°(GeBr , l) value obtained from our data
f
4
20.00
14.8
105
7.67
2.41
(
see below) and enthalpies of reactions (1)–(3) can be
2
3
3
4
5.00
0.00
5.00
0.00
20.2
193
11.6
3.85
used to calculate the standard enthalpy of formation of
solid germanium dibromide,
25.2
307
15.7
5.47
29.8
444
19.9
7.24
∆fH°(GeBr , s) = ∆ H°(GeBr , l)
2
f
4
34.0
604
24.2
9.09
(4)
–
∆H° – ∆H° + ∆H°.
45.00
0.00
60.00
37.8
784
28.4
11.0
1
2
3
5
41.3
982
32.6
13.0
The enthalpy of formation of liquid germanium tet-
rabromide (∆ H°(GeBr , l)) was determined from the
47.20
52.10
56.22
59.75
62.79
67.76
71.54
74.68
77.40
80.01
82.94
86.06
89.15
92.11
1425
1923
2465
3045
3658
4966
6361
7824
9345
10920
12550
14240
15990
17800
40.67
48.32
55.56
62.39
68.84
80.75
91.49
101.26
110.21
118.50
126.26
133.61
140.62
147.34
16.91
20.85
24.74
28.55
32.26
39.37
46.06
52.36
58.29
63.91
69.23
74.29
79.12
83.76
f
4
thermodynamic information about the Ge–Br system
obtained by us in [7–12]. The static method for vapor
pressure measurements allowed us to determine the
thermodynamic characteristics of reactions with the
participation of the gas phase [7, 8],
7
8
9
0.00
0.00
0.00
100.00
1
1
1
1
20.00
40.00
60.00
80.00
GeBr (s) = GeBr (g),
(5)
(6)
(7)
(8)
4
4
GeBr (l) = GeBr (g),
4
4
GeBr (g) = GeBr (g) + Br (g),
4
2
2
Ge(s) + GeBr (g) = 2GeBr (g).
200.00
20.00
240.00
4
2
2
The entropies and heat capacities of gaseous germa-
nium bromides were determined using the statistical
method for thermodynamic function calculations in the
rigid rotator–harmonic oscillator approximation [9,
2
2
2
60.00
80.00
1
0]. The temperature dependence of the heat capacity
98.15 94.59 ± 0.2 19500 ± 50 153.20 ± 0.2 87.81 ± 0.2
of condensed germanium tetrabromide was measured
by adiabatic calorimetry over the temperature range 5–
300.00
14.70
94.83
96.66
19670
21080
153.79
158.37
88.21
91.38
3
15 K [11] and drop calorimetry over the temperature
3
range 303–427 K [12]. To summarize, the following
thermodynamic data were obtained for the Ge–Br sys-
tem (S° and C in J/(mol K) and ∆H° in kJ/mol) [12]:
p
–1
6
–2
–5
2
–
6507T + 0.1594 × 10 T + 0.946 × 10 T (16)
4
–1
C°(GeBr , s) = 561.375 – 0.6842T – 6.67 × 10 T
p
4
(298.15–1500 ä),
(9)
(
273–299 K),
S°(GeBr , g, 298.15) = 396.1 ± 5,
(17)
(18)
4
S°(GeBr , s, 298.15) = 247.4 ± 0.2,
(10)
(11)
4
–2
C° (GeBr , g) = 66.24 – 1.109 × 10 T
p
2
∆fusH°(GeBr , 299.27) = 12.85 ± 0.03,
4
–
1
5
–2
–5
2
–
2450T + 0.459 × 10 T + 0.514 × 10 T
298.15–1500 ä),
C° (GeBr , l) = 157.15 ± 1.5,
(12)
p
4
(
–
1
C°(GeBr , s) = 126.5 – 0.0197T – 9654.8T
S°(GeBr , g, 298.15) = 318.2 ± 3,
(19)
(20)
(21)
(22)
(23)
p
2
2
(13)
(
230–409 K),
∆ H°(GeBr , 298.15) = 58.6 ± 1.2,
sub
4
S°(GeBr , s, 298.15) = 153.2 ± 0.2,
(14)
(15)
2
∆ S°(GeBr , 298.15) = 145.6 ± 3.8,
sub 4
∆fusH°(GeBr , 409.15) = 11.6 ± 0.2,
2
∆ H°(GeBr , 299.27) = 46.6 ± 0.3,
vap 4
–
1
C° (GeBr , g) = 128.26 – 0.244 × 10 T
p
4
∆ S°(GeBr , 299.27) = 104.6 ± 0.8,
vap 4
RUSSIAN JOURNAL OF PHYSICAL CHEMISTRY Vol. 80 No. 12 2006

1
914
ZELENINA et al.
GeBr (g) = GeBr (g) + Br (g)
tions studied did not exceed the limiting measurement
4
2
2
pexpt –pcalcd, torr
errors, which was evidence of the absence of serious
systematic errors in our experiments. By way of
example, such deviations are shown in the figure for
reaction (8).
1.5
1.0
0.5
0
1
2
3
The enthalpy of formation of liquid germanium tet-
rabromide obtained when consistency was attained was
used to calculate the enthalpy of formation of solid ger-
manium dibromide according to (4). Equation (13) was
used to determine the enthalpy of formation and abso-
lute entropy of liquid germanium dibromide at the tem-
perature of fusion.
–
–
–
0.5
1.0
1.5
The consistent standard enthalpies of formation and
absolute entropies of germanium bromides are listed in
Table 3.
4
00
600
800
1000
1200
1400
T, ä
Deviations of experimental pressures from values calcu-
lated using the consistent set of thermodynamic character-
istics (Table 3) for reaction (8) in the Ge–Br system for
three series of measurements.
ACKNOWLEDGMENTS
This work was financially supported by the “State
Program for Support of Leading Scientific Schools,”
project NSh no. 1042 2003.3.
∆r7 H° = 250.3 ± 6.1,
(24)
298
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–
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S°(298.15),
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1
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140.0 ± 4.5*
76.8 ± 6.2
153.2 ± 0.5
210.6 ± 0.5*
317.5 ± 2.6
247.41 ± 0.2
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2
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365.3 ± 4.1
352.4 ± 4.1
306.0 ± 5.8
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(
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1
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Note: The asterisked values correspond to Tfus = 409.15 K.
RUSSIAN JOURNAL OF PHYSICAL CHEMISTRY Vol. 80 No. 12 2006