[cryogenus]

I'm trying to write the balanced quations for the reaction of permanganate with acid gases such as SO2, NO and NO2.
All seems OK with SO2 and NO but not with NO2 as the nett potential seems to come out negative suggesting the reaction will not occur spontaneously.

Reactions with oxidising agents ( potassium permanganate )

NO(g) + MnO4-(aq)  >>  NO3-(aq)  + MnO2(s)    (1)

3 NO2(g) + MnO4-(aq) + H2O(l)  >>  3 NO3-(aq) + MNO2(s) + 2 H+  ( 2 )

3 SO2(g) + 2 MnO4-(aq) + 4 H2O(l)  >>  3 SO4-(aq) + 2 MNO2(s) + 4H+  ( 3 )

REDOX half-reactions:
      
MnO4- + 4H+ + 3e-  >>  MnO2(s) + 2 H2O(l)    Eo = + 1.69 V

NO3- + 4H+ + 3e-  >>  NO(g) + 2 H2O(l)    Eo = + 0.957 V

NO3- + 2H+ + e-  >>  NO2(g) +  H2O(l)    Eo = + 0.78 V

SO4- + 4H+ + 2e-  >>  SO2(g) + 2 H2O(l)    Eo = + 0.172 V
 

Nett change in redox potential for reaction ( 1 ) is 1.69 – 0.957 = + 0.733 V
Nett change in redox potential for reaction ( 2 ) is 1.69 – 3 x 0.78 =  - 0.65 V
Nett change in redox potential for reaction ( 3 ) is 2 x 1.69 – 3 x 0.172 =  + 2.864 V

What bothers me is the negative value for equation (2)
Does this mean permanganate cannot be effective at ambient conditions for removing NO2 in an absorption tower ?

Any help with the redox potential most appreciated
Thanks

[UG]

Nett change in redox potential for reaction ( 1 ) is 1.69 – 0.957 = + 0.733 V
Nett change in redox potential for reaction ( 2 ) is 1.69 – 3 x 0.78 =  - 0.65 V
Nett change in redox potential for reaction ( 3 ) is 2 x 1.69 – 3 x 0.172 =  + 2.864 V

You don't need to multiply by the reaction coefficients when calculating the EMF for (2) and (3). They are simply 1.69 - 0.78 and 1.69 - 0.172

[AndersHoveland]

One way of approaching the reaction-

KMnO4 = KO, MnO2, O

2 NO2 + H2O + O = 2 HNO3

KO + NO2 = KNO3

KMnO4 + 3 NO2 + H2O --> KNO3 + MnO2 + 2 HNO3