Chemistry Reference
In-Depth Information
600
600
400
400
200
0
0
200
400
Temperature (°C)
200
0
240
280
320
360
Wavelength (nm)
Figure 4.19.
The spectrum of
•
OH as a function of temperature; (
) 30°c; (
) 200°c;
(
) 300°c, (
) 350°c. Inset: changes of Epsilon at 250 nm for
•
OH versus temperature
(adapted from Janik et al. [274] with the permission of the American chemical Society).
The
•
OH radical may also react with H
2
O
2
to form
HO
•
(Eq. 4.53). This
study of the
•
OH radical at high temperature was able to model the radiation-
induced chemistry in heat transport piping of the nuclear power plant reactor
[274].
The acid dissociation constants of the
•
OH radical (Eq. 4.57) have been
measured over the temperature range 284-343 K [276]:
•
•−
+
OH
O
+
H
.
K
(4.57)
a
At 298 K, p
K
a
and Δ
ion
G
o
were determined as 11.54 ± 0.04 kJ/mol and
65.9 ± 0.3 kJ/mol, respectively. The values of
∆
ion
S
298
for the
•
OH
radical were calculated as 24.85 ± 0.5 kJ/mol and −139 ± 2 J/mol, respectively
[276].
o
H
298
and
∆
ion
o
4.4.2 Reactivity
The reactivity of
•
OH has been studied using pulse radiolysis technique, γ
radiation, and Fenton reactions [277, 278].
•
OH radical behaves as an electro-
phile and shows some selectivity in the kind of bonds with which it will react;
however,
•
OH generally reacts rapidly and nonselectively with most electron-
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