Multicomponent Equilibrium Thermodynamics - Elements of Environmental Engineering: Thermodynamics and Kinetics - page 60

TABLE 3.8
Antoine Constants for Some Environmentally
Significant Compounds
Compound Range of T ( ◦ C) A B C

Organic compounds
Chloroform

− 35-61 6.493 929.4 196.0

Benzene 8-103 6.905 1211.0 220.8

Biphenyl 69-271 7.245 1998.7 202.7

Naphthalene 86-250 7.010 1733.7 201.8

Tetrachloroethylene 37-120 6.976 1386.9 217.5

Pyrene 200-395 5.618 1122.0 15.2

p -Dichlorobenzene 95-174 7.020 1590.9 210.2

Pentafluorobenzene 49-94 7.036 1254.0 216.0

Inorganic compounds
Nitrogen 7.345 322.2 269.9

Carbon dioxide 9.810 1347.7 273.0

Hydrogen peroxide 7.969 1886.7 220.6

Ammonia 9.963 1617.9 272.5

Sulfur dioxide 7.282 999.9 237.2

If P 1 = 1 atm (as for most environmental engineering problems), T 1 = T b , the normal

boiling point of the liquid, and hence

ln P ∗ =− Δ

RT + Δ

H m H m

RT b .

(3.37)

Within our approximation if we plot ln P versus 1 /T , we should get a straight line
with a slope

Δ H m /R and a constant intercept of Δ H m /RT b , that is, vapor pressures

of liquids and solids vary as ln P i ≈

−

A B/T . If the temperature range is significant

constant, then the acceptable form of fitting the ln P i versus T data
is given by the Antoine equation .

Δ =

such that H

B

ln P i = A −

C ,

(3.38)

t +

where t is usually expressed in Celsius. A , B , and C are constants specific for a
compound. Table 3.8 lists the values for some selected compounds.
For the solid-vapor equilibrium involving the direct transition from solid to vapor
(sublimation), the heat of sublimation is composed of two parts, that is, the heat of
melting (solid to sub-cooled liquid) and the heat of vaporization of the sub-cooled
liquid. If the temperature over which the vapor pressure of a solid is being monitored
includes the melting point ( T m ) of the solid, then the ln P i versus 1 /T curve will
show a change in slope at T m . We consider the pure liquid as the reference phase
for chemical potential and fugacity when calculating free energy changes for phase
transferprocesses.Forcompoundsthataresolidsatroomtemperature,theappropriate
choice is the hypothetical standard state of the sub-cooled liquid.