Chemistry Reference
In-Depth Information
an equilibrium dissociation reaction with parameters characterizing the thermody-
namics of “solid reagent
gaseous products” reactions by making use of methods
developed in the theory of transport processes in dispersion systems [21].
In the case of the practically interesting dissociative sublimation of ammonium
salts with the formation of ammonia and acid, these expressions are
→
Dr
√
A
ρ
R
T
S
b
2
exp
−
Δ
H
2R
T
S
U
≈
(1.59)
and
r
√
A
ξ
exp
,
−
Δ
H
2R
T
S
≈
U
(1.60)
b
2
where
A
is the preexponential factor in the expression for the equilibrium constant,
ξ
H
is the dissociation heat, and
r
is the radius (effective) of the escape channel for the gas.
Relationship (1.59) corresponds to a relatively low pressure of gaseous products
from the thermodynamically equilibrium process,
P
S
(
P
S
<<
P
∞
). The reaction prod-
ucts are eliminated from the reaction zone due to diffusion-assisted transport (
D
is
the diffusion coefficient). Relationship (1.60) is valid in the case of relatively high
P
S
(
P
S
is the coefficient of resistance in the Darcy law,
Δ
≥
P
∞
) for hydrodynamic transport of the reaction products.
References
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PA , p 3
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