Thermodynamics of Biological Reactions. Methanogens and Sulfate Reducing Bacteria (SRB) are anaerobic organisms typically coexisting in swamps and in anaerobic digesters. We can use thermodynamic principles to understand some basic concepts of the survival and competition of both organisms in these environments.

In anaerobic environments containing sulfate, SRB and methanogens compete for the hydrogen available.

A balanced reaction for SRB activity is the following:

4H2 + SO4 2- + H+ HS- + 4H2O

A balanced reaction for methanogenic activity is the following:

CO2 + 4H2 CH4 + 2H2O

For each reaction:

a) Determine G o .

b) Determine G o .

) Assuming neutral pH, 35 C, concentrations of sulfate and hydrogen sulfide of 1 and 5 mM, respectively, and partial pressures of CO2 and CH4 of 0.4 atm and 0.6 atm, respectively, determine the minimum H2 partial pressures at which methanogenic and SRB activity would