108
Chapter 4
Schill
et al.
(1999) made an experimental and theoretical study of this rather strange microorganism for
which the growth associated heat production is inordinately high - as implied by the name of the
organism. The reaction temperature was 60°C and to calculate the heat of reaction and the free energy
change associated with eq. (1) the thermodynamic data of Table 4.3 must be corrected.
The change in heats of combustion with modest changes of temperature is negligible - for example for
the heat of combustion of Hi to form liquid water:
1
(-A H c)m K -{ -A H e)mK
=(7 + f 7-9X 333-298)+ (563-582). 18 = -289 cal mole
1
(2)
The first term in (2) is Aa AT, where Aa is the change in molar specific heat by the reaction. The second
term derives from the change in heat of condensation of H20 between 298 and 333 K.
Using the result of Example 4.1
(-
AHe)mK
= (68280 - 289) cal (mole H2)'' = 285 kJ (mole H
, ) 1
The change in free energy is much larger. Thus for the combustion of H
2
which at the reaction temperature
333BC is present in a measured concentration cW
j =
8
-
1 0 " 6
M
in the cytosol of the organism
( - M J m K
-(-A G c)mK
= -ATAS + R T ln(H -cH2)
(3)
H is the Henry’s law coefficient 1250 atm L mole
'1
for solution of H
2
in water at 60°C, A
T=
35K, and A
S
is 39 cal (mol K
.)'1
from Example 4.1 (liquid water).
(-AG
C)333
= 56661-35 -39-1.987 *333 In 100 = 52.2 kcal mole
'1
= 219 kJ mole
'1
(4)
The table below summarizes the thermodynamic data (in kJ (C-mole)'1) used by Schill
et al.
(1999) to
calculate the heat of reaction and free energy change associated with (1). The measured concentration of the
dissolved gases at 333K is also shown.
Comoound
-AH*
-AG,
HifS-lO^M)
285
219
CH4(5.7T0^M)
892
808
CO
2
(1.6T0'
4
M)
0
-
12.8
NH
3
(50 mM)
383
401
Biomass
458
541
Except for the rather low value of (-A
Ht)
for biomass - the value is calculated from a calorimetric
experiment by the authors - the heats of combustion are practically the same as those shown in Table
4.3.
We can now calculate A
H
and AG for the stoichiometry (1)
Q = -A H =
285 + 0.0048 • 383-0.02 ■
458 - 0.240 ■
892 =63.6 kJ (mole H
2)-1