Page 183 - Physical Chemistry

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Chapter 5 Exercise
Standard Thermodynamic
Functions of Reaction For C(graphite), H° m,1000 H° m,298 11.795 kJ/mol and S° m,1000 24.457
J/(mol K). Use these data and data in the example to find G° for C(graphite)
1000
O (g) → CO (g). (Answer: 395.89 kJ/mol.)
2 2
The quantity H° H° is found by integrating C° data from 25°C to T,
m,T m,298 P,m
since (
H/
T) C . We have
P P
1G° H° m,298 2>T 1H° m,T TS° 2>T H° m,298 >T
m,T
m,T
1H° m,T H° m,298 2>T S°
m,T
so (G° H° )/T is found from H° H° and S° data.
m,T m,298 m,T m,298 m,T
The reason for dividing G° H° by T is to make the function vary slowly
m,T m,298
with T, which enables accurate interpolation in the table. Tabulating H° H° and
m,T m,298
(G° H° )/T is convenient because these quantities can be found from properties
m,T m,298
of one substance only (in contrast to H° and G°, which also depend on properties
f f
of the elements), and these quantities are more accurately known than H° and G°;
f f
moreover, these quantities for ideal gases can be accurately calculated using statistical
mechanics (Chapter 21) if the molecular structure and vibration frequencies are known.
If we have thermodynamic data at only 25°C for the reaction species, we need ex-
pressions for C° of the species to find H°, S°, and G° at other temperatures.
P,m
C° polynomials [Eq. (5.20)] are given in O. Knacke et al., Thermochemical Proper-
P,m
ties of Inorganic Substances, 2d ed., Springer-Verlag, 1991, for 900 inorganic sub-
stances; in Lide and Kehiaian for 216 substances; and in Prausnitz, Poling, and
O’Connell for 618 gases. Such polynomials are easily generated from C° -versus-T
P,m
data using a spreadsheet (Sec. 5.6).
A widely used tabulation of thermodynamic data for inorganic compounds, one-
and two-carbon organic compounds, and species (including ions) in aqueous solution is
D. D. Wagman et al., The NBS Tables of Chemical Thermodynamic Properties, 1982,
published by the American Chemical Society and the American Institute of Physics
for the National Bureau of Standards (vol. 11, supp. 2, of J. Phys. Chem. Ref. Data).
These tables list H° , G° , S° , and C° for about 10000 substances.
f 298 f 298 m,298 P,m,298
Thermodynamic data for inorganic and organic compounds at 25°C and at other temper-
atures are given in Landolt-Börnstein, 6th ed., vol. II, pt. 4, pp. 179–474. H° data for
f 298
many organic compounds are tabulated in J. B. Pedley et al., Thermochemical Data of
Organic Compounds, 2d ed., Chapman and Hall, 1986; J. B. Pedley, Thermochemical
Data and Structures of Organic Compounds (TRC Data Series), Springer-Verlag, 1994.
S° and C° data for 2500 condensed-phase organic compounds are given in E. S.
m,298 P,m,298
Domalski and E. D. Hearing, J. Phys. Chem. Ref. Data, 25, 1 (1996).
The National Institute of Standards and Technology (NIST) Chemistry Webbook
(webbook.nist.gov/) gives 25°C thermodynamic data for 7000 organic and inorganic
compounds and gives C polynomial expressions for some substances.
P
Thermodynamic data over wide temperature ranges are tabulated for mainly inor-
ganic compounds in (a) M. W. Chase et al., NIST-JANAF Thermochemical Tables, 4th
ed., 1998, published by the American Chemical Society and the American Institute of
Physics for the National Institute of Standards and Technology; (b) I. Barin,
Thermochemical Data of Pure Substances, 3d ed., VCH, 1995; (c) O. Knacke et al.,
Thermochemical Properties of Inorganic Substances, 2d ed., Springer-Verlag, 1991;
(d) O. Kubaschewski and C. B. Alcock, Metallurgical Thermochemistry, 5th ed.,
Pergamon, 1979.
Thermodynamic data over a range of T are given for organic compounds in
(a)D. R. Stull et al., The Chemical Thermodynamics of Organic Compounds, Wiley,