[dwickham]

It is well known that facultative bacteria will obtain oxygen from nitrate (NO3) for metabolism, but will only do so when no free oxygen is available.  It appears, however, that those same bacteria can obtain oxygen from nitrite (NO2) even if air is present.  Bacteria apparently must transport NO3 through the cell membrane in order to reduce it from NO3 to NO2.  They then have to transport NO2 back outside as a waste product.  So it is a pretty inefficient way to get a singe oxygen ion and it makes sense that bacteria will only do this if no other oxygen is available. 

NO2, however, is processed outside the cell membrane and it contains two oxygen ions, just like free O2 would supply.  My presumption is that is easier to get the oxygen from NO2 than from O2 since O2 has a double bond.  How would I show that this is the case using an energetic equation?  For instance what would the free energy of the covalent bonded N - O be as compared to the free energy of the O = O double bond.and am I right in presuming that oxygen is easier to get from NO2 than O2?