Russian Journal of Applied Chemistry, 2009, Vol. 82, No. 3, pp. 505−508.
Pleiades Publishing, Ltd., 2009.
Original Russian Text
A.I. Vitvitskii, 2009, published in Zhurnal Prikladnoi Khimii, 2009, Vol. 82, No. 3, pp. 511−514.
The boiling curve represents the dependences of
the saturated vapor pressure Р
(Pa) of the individual
substances on the temperature T (K) or the dependence of
the boiling temperature Т
(K) on the pressure P (Pa). In
coordinates Т–Р the boiling curve limited by the critical
point coordinates (Т
) where a boundary between
gas and liquid phases disappears, on the one side and by
coordinates of a triple point where a curves of boiling
(condensation), sublimation, and melting (solidiﬁ cation)
come together, on the other side.
Operating with chemicals a relation of the saturated
vapor pressure and temperature is used for governing
partial pressure of appropriate substances in obtained
gas mixtures, and also for providing ﬂ ame safety and
maximum permissible concentrations in a room. For
noted targets a reliable and accessible information is
required not as discrete experimental points on the boiling
curve but as generalized equation involving a total range
of conditions when gas−liquid transfer occurs.
All attempts to apply the Clausius−Clapeyron
relation for description of the boiling curve resulted by
obtaining semi-empirical equations for the independent
curve sections . A set of the standard conditions in the
equation (2) results in an inevitable exclusions and large
errors for some substances.
A development of a way for description of the whole
boiling curve that requires minimum initial experimental
data is the purpose of our report.
We found that in ln(Р
boiling curves of all substances became straight and can
be simulated by equitype equation looking as
New Equation of Boiling Curve
A. I. Vitvitskii
RSC “Aplplied Chemistry”, St. Petersburg, Russia
Received October 8, 2008
Abstract—A dependence of a saturated vapor pressure of individual substances on a temperature describing this
whole curve was obtained by coordinates of two points on the boiling curve thereby one of these points was
where R = 8.314 J mol
, ΔН was enthalpy of evapora-
tion (J mol
), constant value in a range of the parameters
from the critical point to triple one.
At solution of equation (1) with respect to ΔН its value
can be computed by coordinates of two points, one of
which is critical:
ΔН = R (1/Т
The computed enthalpy of evaporation of the some
substances with use in equation (2) in addition to the
values of Т
, and Р
, normal values of the boiling
at 101.325 kPa) or parameters of the
triple point, i.e. for a temperature range from Т
or for the whole boiling curve are preseted in the table.
The used values of P
, and Т
are from , the
parameters of the triple point from . Inorganic and
organic substances, monoatomic and polyatomic ones,
and also non-polar and polar substances including those
that do not possess T
) are listed in
An average deviation Δ (%) of two computed values of
ΔН from each other (for 18 substances) is less than
0.7 rel % and that does not exceed an error of parameters
used for the calculation (according to data of ,
deviation for Т
equals ±(0.5–1.5)%, for Р
That evidences a constancy of ΔН value in the total range
of conditions for the gas−liquid transfer.