The equilibrium constant K of reaction (2.2.13) is equal to
K ¼
F
2
I
F I 2
expðÀD
0
0 =RTÞ species=cm
3
:
ð2:2:14Þ
Here F I is the partition function of the I(
2 P J ) atoms, F I 2 is the partition function
of the I 2 ðX0
þ
g ; v X ; J X Þ molecule, D
0
0 ¼ 1:542 eV is the dissociation energy of the I 2
molecule at T = 0 K, i.e., from the I 2 ðX; v X ¼ 0; J X ¼ 0Þ state; M partition functions are reduced.
The partition function of an atom is equal to the product of the statistical sums
corresponding to the various forms of its energy:
F ¼ F t Á F e Á F n :
ð2:2:15Þ
Here,
– F t is the partition function corresponding to the translational motion,
– F e is the electronic partition function,
– F n - nuclear partition function.
F t ¼
ð2pmkTÞ
3=2
h 3
Á V
ð2:2:16aÞ
For one mole of an ideal gas and p = 1 (if we need to assume K p ; V = RT/p)
Fig. 2.2 Some potential
energy curves of the valence
iodine molecule states
correlating with the I(
2
P 3/
2 ) + I(
2
P 3/2 ) and I(
2
P 3/2 ) + I
(
2
P 1/2 ) dissociation limits (see
[7], p. 26)
2.2 Chemical Equilibrium. Equilibrium Constant
19