The sequence of organic matter oxidation

The sequence of biological organic matter oxidation (e.g., Schlesinger, 1997) takes place in the following order: by oxygen, by nitrate, by manganese dioxide, by iron (III), by soleplate, and by carbon dioxide. This means that oxygen, if present, will always outcompete nitrate which will outcompete manganese dioxide, and so on. The amount of exergy stored as a result of an oxidation process is measured by the available kJ/mole of electrons which determines the number of adenosine triphosphate (ATP) molecules formed. ATP represents exergy storage of 42kJ/mole. Usable energy as exergy in ATPs decreases in the same sequence as indicated above. This is as expected if the exergy-storage hypothesis (ELT) were valid (Table 1.2). If more oxidizing agents are offered to a system, the one giving the highest storage of free energy will be selected.

In Table 1.2, the first (aerobic) reaction will always outcompete the others because it gives the highest yield of stored exergy. The last (anaerobic) reaction produces methane; this is a less complete oxidation than the first because methane has greater exergy content than water.

Table 1.2 Yields of kJ and ATPs per mole of electrons, corresponding to 0.25 moles of CH2O

oxidized (carbohydrates)

Reaction kJ/mole e ATPs/mole e

Reaction kJ/mole e ATPs/mole e

Table 1.2 Yields of kJ and ATPs per mole of electrons, corresponding to 0.25 moles of CH2O

oxidized (carbohydrates)

ch2o -

O2=CO2

+ H2O

125

2.98

ch2o -

-0.8NO3 "

+ 0.8 H + = CO2 + 0.4 N2 + 1.4 H2

119

2.83

CH2O -

- 2 MnO2 +

H + = CO2 + 2Mn2 + + 3H2O

85

2.02

CH2O -

- 4 FeOOH

- 8H + = CO2 + 7H2O + Fe2 +

27

0.64

CH2O -

-0.5SO42~

+ 0.5 H + = CO2 + 0.5 HS" + H2O

26

0.62

CH2O -

- 0.5 CO2 =

CO2 + 0.5 CH4

23

0.55

Note: The released energy is available to build ATP for various oxidation processes of organic matter at pH = 7.0 and 25°C.

Note: The released energy is available to build ATP for various oxidation processes of organic matter at pH = 7.0 and 25°C.

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Solar Panel Basics

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