Redox reaction identification

[lazybutt26]

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Hi guys!
I am given this equation: 3NO2+H2O-> 2HNO3+NO and asked to identify if this is redox reaction.
I've assigned each atoms its oxidation numbers and found out that O and H do not experience any oxidation number change except for N.
Since I thought that there should be two atoms with oxidation number changes(given oxidation and redux should happen simultaneously), I chose my answer to "No, this is not a redox reaction"
But I was WRONG! It says if at least one atom has oxidation number change, then it's considered a redox reaction. But this doesn't make any sense to me. If N has gone from oxidation number +4-> +5, losing one electron, there should be an atom gaining electrons, shouldn't there? O and H stay the same in terms of oxidation numbers, unless I've calculated them wrong.

Please help! I need to know if this is true: As long as one atom has oxidation number change, it's considered redox reaction?!

Thanks so much for your help!

 

[Mariolee]

Although it's only the N atom, N in NO2 has an oxidation number of +4, N in HNO3 has an oxidation number of +5, N in NO has an oxidation number of +2. In this case, N is both oxidized (+4 -> +5) and reduced (+4 -> +2).

So there is both a reduction and an oxidation to different N atoms.

Source: https://answers.yahoo.com/question/index?qid=20110504095541AAkMMUH

 

[aldol16]

This is called a disproportionation reaction and N is both oxidized and reduced. You didn't account for NO.