1070-4272/04/7701-0023C2004 MAIK [Nauka/Interperiodica]
Russian Journal of Applied Chemistry, Vol. 77, No. 1, 2004, pp. 23!25. Translated from Zhurnal Prikladnoi Khimii, Vol. 77, No. 1,
2004, pp. 25!27.
Original Russian Text Copyright + 2004 by Sladkov, Uchaneva.
OF SYSTEMS AND PROCESSES
Iteration Methods for Calculating Physicochemical Properties
of Molecular Inorganic Compounds
I. B. Sladkov and M. V. Uchaneva
St. Petersburg State Polytechnic University, St. Petersburg, Russia
Received May 26, 2003
Abstract-Iteration schemes for highly reliable prediction of physicochemical properties of molecular in-
organic compounds were proposed.
The most reliable prediction of physicochemical
properties of molecular liquids is achieved using
methods based on the thermodynamic similarity
theory. These methods use relationships between the
physicochemical properties expressed in the dimen-
sionless form. Passing to dimensionless values re-
quires data on the critical parameters of substances.
Therefore, the above methods employ critical param-
eters as input data. Because the experimental data on
the critical constants are rather limited, the calculation
methods of their determination have became practical-
ly significant. First, this concerns the molecular in-
organic compounds that have found wide practical
application  but are, however, little studied.
Reliable data on the critical parameters can be ob-
tained by the iteration methods. These methods in-
volve successive approximations to obtain the closest
agreement between the required parameter and other
previously known physicochemical properties of a
substance. The fact that not only the critical param-
eters but also other physicochemical properties of a
substance can be determined in the course of iteration
is a significant advantage of the iteration methods.
In this study we developed an iteration scheme for
highly reliable prediction of the critical parameters of
molecular inorganic compounds. It is based on rela-
tionships employing the determining criterion, which
reliably describes the thermodynamic similarity of any
molecular inorganic compounds. The latter is referred
to as the factor of the complexity of intermolecular
interaction (or y-factor) and is considered in detail
Let us list the equations used in the iteration
scheme proposed (iteration 1). For the critical tem-
perature and critical pressure, we used the equation
obtained by integrating the Clausius3Clapeyron equa-
tion between the boiling and critical temperatures .
In this case, the pressure varies from a value at the
boiling point P
to a value at the critical point P
the literature , this equation is known as the van der
! 1). (1)
f = ,H
is referred to as the generalized constant, because its
variations from substance to substance lie within very
narrow limits. DH
is the enthalpy of vaporization
at the boiling point.
To leave only one unknown parameter (critical
temperature) in Eq. (1), the known relationship for
the critical pressure is used:
where b is the van der Waals constant.
Then, Eq. (1) becomes
)] = f(T
! 1). (4)
The critical temperature appearing in the expres-
sion for f can be calculated by the equation 
where y is the factor of the complexity of inter-
The y factor is the determining criterion of thermo-
dynamic similarity, which extends the applicability of