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1969 (gas-phase data); (b) Selected Values of Properties of Hydrocarbons and Related Section 5.10
Compounds, 1966–1985, Selected Values of Properties of Chemical Compounds, Estimation of Thermodynamic
Properties
1966–1985, TRC Thermodynamic Tables—Hydrocarbons, 1985–, TRC Thermo-
dynamic Tables—Non-Hydrocarbons,1985–, all published in loose-leaf form by the
TRC Group (trc.nist.gov/DEFAULT.HTM); (c) M. Frenkel et al., Thermodynamics of
Organic Compounds in the Gas State, Vols. I and II (TRC Data Series), Springer-
Verlag, 1994.
Thermodynamic data for biochemical compounds are tabulated by R. C. Wilhoit
in chap. 2 of H. D. Brown (ed.), Biochemical Microcalorimetry, Academic Press,
1969; see also H.-J. Hinz (ed.), Thermodynamic Data for Biochemistry and
Biotechnology, Springer-Verlag, 1986; R. A. Alberty, Thermodynamics of Biochemical
Reactions, Wiley, 2003 (see also library.wolfram.com/infocenter/MathSource/797/).

5.10 ESTIMATION OF THERMODYNAMIC PROPERTIES

7
About 3 10 chemical compounds are known, and it is likely that H°, S° , C° ,
f m P,m
and G° for most known compounds will never be measured. Several methods have
f
been proposed for estimating thermodynamic properties of a compound for which data
do not exist. Chemical engineers often use estimation methods. It’s a lot cheaper
and faster to estimate needed unknown thermodynamic quantities than to measure
them, and quantities obtained by estimation methods are sufficiently reliable to be
useful for many purposes. An outstanding compilation of reliable estimation methods
for thermodynamic and transport properties (Chapter 15) of liquids and gases is
Liquid at 1 bar
Prausnitz, Poling, and O’Connell.
(a)
Bond Additivity
Many properties can be estimated as the sum of contributions from the chemical
bonds. One uses experimental data on compounds for which data exist to arrive at Liquid at P vp
typical values for the bond contributions to the property in question. These bond con-
tributions are then used to estimate the property in compounds for which data are un- (b)
available. It should be emphasized that this approach is only an approximation.
Bond additivity methods work best for ideal-gas thermodynamic properties and
Vapor at P
usually cannot be applied to liquids or solids because of the unpredictable effects of vp
intermolecular forces. For a compound that is a liquid or solid at 25°C and 1 bar, the
ideal-gas state (like a supercooled liquid state) is not stable. Let P be the liquid’s (c)
vp
vapor pressure at 25°C. To relate observable thermodynamic properties of the liquid
at 25°C and 1 bar to ideal-gas properties at 25°C and 1 bar, we use the following
Vapor at 0 bar
isothermal process at 25°C (Fig. 5.13): (a) change the liquid’s pressure from 1 bar to
P ; (b) reversibly vaporize the liquid at 25°C and P ; (c) reduce the gas pressure to
vp vp
zero; (d) wave a magic wand that transforms the real gas to an ideal gas; (e) compress (d)
the ideal gas to P 1 bar. Since the differences between real-gas and ideal-gas prop-
erties at 1 bar are quite small, one usually replaces steps (c) , (d), and (e) with a com- Ideal vapor at 0 bar
pression of the gas (assumed to behave ideally) from pressure P to 1 bar. Also, step
vp
(a) usually has a negligible effect on the liquid’s properties. Thus, knowledge of H
m (e)
of vaporization enables estimates of enthalpies and entropies of the liquid to be found
from estimated ideal-gas enthalpies and entropies. Methods for estimation of H
vap m
are discussed in Prausnitz, Poling, and O’Connell, chap. 7. Ideal vapor at 1 bar
Benson and Buss constructed a table of bond contributions to C° , S° , and
P,m,298 m,298
H° for compounds in the ideal-gas state [S. W. Benson and J. H. Buss, J. Chem. Figure 5.13
f 298
Phys., 29, 546 (1958)]. Addition of these contributions enables one to estimate ideal-
Conversion of a liquid at 25°C and
gas S° and C° values with typical errors of 1 to 2 cal/(mol K) and H° val-
m,298 P,m,298 f 298 1 bar to an ideal gas at 25°C and
ues with typical errors of 3 to 6 kcal/mol. It should be noted that a contribution to 1 bar.