pe = Log KR + Log [(Aox)m/(Ared)p] npH 1/2 H2O 1/4 O2 + H+ + e- (Log KR = 20.8, PO2= 0.21atm) 1/5 NO3- + 6/5 H+ + e- 1/10 N2 + 3/5 H2O (Log KR = 21.1; PN2= 0.79atm NO3- = 10-3 moles L-1) FeOOH + 3H+ + e- Fe2+ + 3/2H2O (Log KR = 13.4; Fe2+ = 10-3 moles L-1 )

(a) pe at which H2O is oxidized to O2 at pH 7. (b) pe at which NO3- is reduced to N2 at pH 7. (c) pe at which FeOOH is reduced to Fe2+ at pH 7. 2+