[AmCoop97]

Chemolithotrophic bacteria use inorganic compound as both electron donor and electron acceptor. However, electron transport from acceptor to donor must be thermodynamically favorable. The favorability depends on concentrations of reactants and pH of the environment in which a microorganism lives. You goal is to determine whether chemolithotrophic bacteria can grow using the following chemical reaction in an aquatic environment (aquatic sediment):
NH3 + Fe2O3    =   N2 + Fe2+
When pH of the environment is (a) pH7.0 and (b) pH4.0 under normal pressure and temperature and concentrations:
[NH3] = 10 mM
[N2] = 0.48 mM
[Fe2+] = 0.4 M
Fe2O3 – solid
55.5 moles of Water
Instructions:
1. Thoroughly read Appendix 1, follow point by point. Missing DeltaGfo  (also called Gfo in the Appendix 1) for Fe2O3 can be downloaded from the Internet.
2. Balance the equation. If you don’t balance the equation, any calculation will be wrong!
3. Do not put pH in calculations twice. If you use DeltaGo’ do not put [H+] in calculation of the equilibrium constant K. However, if you are using DeltaGo instead, the equilibrium constant should include [H+].

INFORMATION GIVEN FROM APPENDIX 1:

FREE ENERGIES OF FORMATION (Gf) FOR SOME SUBSTANCES (kJ/mol)

Fe2+ -78.87

H2O -237.17

Fe2O3 -740

NH3 -26.57

(1.) Balance the equation

(2.) Calculate deltaG0

(3.) Calculate deltaG

(4.) Make judgment whether the reaction is possible based on the deltaG value for the reaction

[Borek]

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