Belay Zeleke Dilnesa - Eawag-Empa Library

CHAPTER 2 MATERIALS AND METHODS
0
that the heat capacity of the reaction, rC p , is constant in the considered temperature
range.
A2
A0
A lnT
;
T
log KT 3
0.
4343
R
0
0
SCp 1lnT
A0 r T0
r T0
0.
4343
R
0
0
H Cp T
A2 r T0
r T0
0.
4343
A
R
0
3 r T0
Cp
T
ln
0 0
0
rST
rST
Cp
0 r T0
T0
0
0
0
rH
T rH
T Cp ( 0 r T0
0
G H T
r
0
T
r
0
T
r
S
0
T
T T
)
0
0
where T0 is the reference temperature (298.15 K), S0 the entropy, H 0 the enthalpy and G 0
the Gibbs free energy. A more detailed description of the temperature corrections used in
GEMS is given elsewhere [50] and in the online documentation of GEMS. The value of
0
the heat capacity of the reaction, rC p , has little influence on the calculated log K values
in the temperature range 0-100 °C. Generally, the difference between the 3-term
extrapolation and the more complete description using 7 terms is usually negligible in the
temperature range from 0 to 100 °C [51].
The entropy S° was adjusted to obtain the best fit between the measured solubility data at
different temperatures and the calculated solubility products. As only solubility products
at two or three different temperatures were available, only the entropy was fitted, while
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