THE STANDARD ENTHALPIES OF COMBUSTION
869
Measured heats of combustion of cobalt tetrakis(4-metoxy-
phenyl)porphin complex
tiated by discharging a capacitor onto a piece of copper
wire with the specific heat of combustion 2510.0
2.1 kJ/kg. The correction for the heat of combustion
was determined experimentally and included in calcu-
lations of the energy of combustion of the substance.
Once the experiment was complete, the calorimetric
bomb was connected to a system of absorption tubes for
determining carbon dioxide. An analysis of the prod-
ucts of the reaction
qHNO , kJ
m, g
∆Tcorr, µV
–∆UB, kJ/mol
3
0.02900
0.03564
0.05249
0.10288
0.11809
110.00
150.66
221.97
415.52
498.05
0.00217
0.00262
0.00391
0.00766
0.00879
27731.51
27645.43
27741.07
27669.37
27712.23
C48H36N4O4CO(cr) + 55.5O2(g)
(1)
(27699.92 50.98)
= 48CO2(g) + CoO(cr) + 18H2O(liq) + 2N2(g)
Note: m is the sample weight of cobalt tetrakis(4-metoxyphe-
nyl)porphin complex, ∆T is the corrected temperature
for CO2 by the Rossini method [6] showed that the ratio
of the weight of carbon dioxide formed in combustion
to that calculated for the reaction was within the range
0.9993–1.0005. This is solid evidence for reaction com-
pleteness. The amount and composition of the dry resi-
due (CoO) was determined by atomic absorption anal-
ysis.
corr
rise, and qHNO is the correction for the formation of
3
HNO (sln). The error in the arithmetic mean was calculated
3
2
1/2
by the formula s = t [Σ∆ /n(n – 1)] , where t is the Stu-
p, n
p, n
dent test value at a 0.95 confidence probability and n is the
number of experiments. The average value is parenthesized.
A small amount of nitrogen present in the com-
pound was found in the reaction products as nitric acid
formed by the reaction
The experimental data on the heat of combustion of
CoT(n-MeOPh)P were used to calculate its standard
thermodynamic characteristics. For the crystalline state
at 298.15 K, we obtained: the standard enthalpy of
combustion ∆ÒH° = –27334.06 50.98 kJ/mol, and
∆fH° = 3062.90 50.97 kJ/mol.
0.5N2(g) + 1.25O2(g) + 0.5H2O(liq)
(2)
= HNO3(aq. sln).
The heat effect of the reaction at 298.15 K and
500-fold dilution with ç2é is 64.0 kJ/mol [7]. In calcu-
lations of ∆UÇ, a correction for the heat of formation of
HNO3 (sln) was introduced; the correction was no
larger than 0.2% of the measured heat effect. The
amount of the acid was determined by titration of wash
water from the bomb with a solution of NaOH. The
experimental data on the energy of combustion of the
substance according to reaction (1) are presented in the
table.
ACKNOWLEDGMENTS
This work was financially supported by the Depart-
mental Special Purpose Program “Development of the
Scientific Potential of Higher School in 2006–2008.”
REFERENCES
1. D. R. Zakirov, D. B. Solomin, A. Volkov, et al., Zh. Fiz.
Khim. 73 (12), 2272 (1999) [Russ. J. Phys. Chem. 73
(12), 2058 (1999)].
The standard enthalpy of combustion was deter-
mined taking into account the Washburn correction [8]
by the equation
2. D. R. Zakirov, M. I. Bazanov, A. Volkov, et al., Zh. Fiz.
Khim. 74 (9), 1899 (2000) [Russ. J. Phys. Chem. 74
(10), (2000)].
∆cH° = ∆cU° + ∆nRT,
where ∆n is the change in the amount of gases (mol) in
combustion reaction (1). The Washburn correction was
0.0137% of the ∆UÇ value.
3. D. R. Zakirov, M. I. Bazanov, A. Volkov, et al., Zh. Fiz.
Khim. 77 (6), 1136 (2003) [Russ. J. Phys. Chem. 77 (6),
1022 (2003)].
The standard enthalpy of formation of the substance
was calculated by the equation
4. A. S. Semeikin, O. I. Koifman, and B. D. Berezin, Khim.
Geterotsikl. Soedin, No. 6, 798 (1986).
5. N. Datta-Gupta and T. J. Bardos, Pharm. Sci. 57, 300
∆fH°(C48H36N4O4Co(cr, 298 K))
= 48∆fH°(CO2(g, 298 K))
(1968).
6. D. Rislove, A. T. O' Brien, and J. M. Sugihara, J. Chem.
Eng. Data 13 (4), 588 (1968).
+ 18∆fH°(H2O(liq, 298 K))
+ ∆fH°(CoO(cr, 298 K))
(3)
7. Thermal Constants of Substances: A Handbook, Ed. by
V. P. Glushko (VINITI, Moscow, 1968), Vol. 3, p. 83 [in
Russian].
– ∆cH°(C48H36N4O4Co(cr, 298 K)).
8. S. M. Skuratov, V. P. Kolesov, and A. F. Vorob’ev, Ther-
mochemistry (Mosk. Gos. Univ., Moscow, 1966) [in
Russian].
The ∆fH° values for ëé2, ç2é, and CoO were taken
from the handbook [7].
RUSSIAN JOURNAL OF PHYSICAL CHEMISTRY A Vol. 83 No. 5 2009