1070-4272/05/7805-0707+2005 Pleiades Publishing, Inc.
Russian Journal of Applied Chemistry, Vol. 78, No. 5, 2005, pp. 707!710. Translated from Zhurnal Prikladnoi Khimii, Vol. 78, No. 5,
2005, pp. 721!724.
Original Russian Text Copyright + 2005 by Demidov, Markelov.
OF SYSTEMS AND PROCESSES
Thermodynamics of Reaction of Carbon with Oxygen
A. I. Demidov and I. A. Markelov
St. Petersburg State Polythechnic University, St. Petersburg, Russia
Received April 7, 2005
Abstract-The standard Gibbs energies of reactions proceeding in the C!O system are calculated per mole of
carbon dioxide, per mole of the reaction product, and per mole of atoms of the initial substances. A compara-
tive analysis of the calculation results is made.
The reactions of carbon with oxygen can be de-
scribed by the following equations [1!5]:
2C + O
= 2CO, (1)
= 2CO, (3)
2CO + O
These reactions are of practical significance for
metallurgical, chemical, and fuel industry. The input
data for calculating the standard Gibbs energy of the
reactions were taken from a reference book . The
thermodynamic calculation of the Gibbs energy of
reactions (1)!(4) per mole of oxygen [reactions (1),
(2), (4)] or per mole of carbon dioxide [reaction (3)],
as it was done in [2!6], yields the results given in
Table 1 and Fig. 1.
In the range 298!2500 K, reactions (1), (2), and (4)
are characterized by the negative standard Gibbs
energy, and, consequently, by the high yield of the
reaction products. The more negative the ,G
the higher the yield of the reaction products . The
standard Gibbs energy of reaction (3) (straight line 3)
is negative above 1000 K. At the same time, the posi-
values do not show that the reaction is im-
probable; they only show that the yield of the reaction
products is very low .
Straight lines 1, 2, and 4 (Fig. 1) intersect at a
temperature of about 1000 K. To the right from the
interception point, straight line 1 passes below two
others. This means that, above 1000 K, the chemical
affinity of carbon for oxygen under conditions of CO
formation is maximal. To the left from the intercep-
tion point, i.e., below 1000 K, the most negative is the
standard Gibbs energy of reaction (4). At temperatures
of about 2100 K, straight lines 3 and 4 intersect.
Above 2100 K, CO rather than CO
thermodynamically stable oxide.
The reactions in the C!O system can also be related
to 1 mol of the reaction product [8, 9]:
C + 1/2O
= CO, (1<)
1/2C + 1/2CO
= CO, (3<)
CO + 1/2O
The results of the thermodynamic calculation of the
standard Gibbs energy of reactions (1<)!(4<) are
given in Table 1 and Fig. 2. As seen from Fig. 2,
reaction (2<) (straight line 2<) is characterized by the
lowest standard Gibbs energy in the range 298!
2500 K. This means that, in the reaction of carbon
with oxygen over the entire temperature range studied,
, kJ mol
Fig. 1. Standard Gibbs energies ,G
of reactions (1)!(4)
vs. temperature T.