Answer to Question #108648 in Molecular Biology for amir

Question

The standard potentials (at pH = 7) are given for some important donors and
acceptors:
Reduced Species, Oxidized Product, Potential( V)
H2, H -041
H2O, 02, +0.822
H2 S, so4, -0.22
N2, No3, +0.75
Fe2+, Fe3+, +0.77
CH4 ,CO2, -0.24
Compute the overall standard potential (at pH 7) for transfer of electrons from
the follow pairs ofdonors and acceptors. Rank them from most energetic (most
positive) to least energetic: H2/Fe3+, H2S/02, CH4IN03", H2/02, Fe2+102,
and H2SIN03"

Answer 1

For the reaction

E⁰_r=E^O(Ox₁/Red₁)-E^O(Ox₂/Red₂)

-E^o_r=E⁰_ox-E⁰_red

E⁰_r(H₂/Fe³⁺)=+0,77-(-0,41)=1,18 V

E(H₂S/O₂)=+0,822-(-0,22)=-1,042V

E(CH₄/NO₃^-)=+0,75-(-0,24)=0,99V

E(H₂/O₂)=0,822-(-0,41)=1,232V

E(Fe²⁺/O₂)=0,822-0,77-=0.052V

E(H₂S/NO₃^-)=+0.75-(-0.22)=0,97V