balance equations?

Question

how do you balance this
NO2+ O+H2O---- HNO3

Answer 1

NO2 + H2O + O2 ====> HNO3 would be the correct equation (Oxygen gas is diatomic), now let's try to balance it:

Since we have two hydrogens in the water molecule, let's start with two hydrogens from the nitric acid, i.e. - two molecules of HNO3:

x NO2 + H2O + yO2 ===> 2 HNO3

That means we'll need to have 2 hydrogens, 2 nitrogens, and 6 oxygens.

In order to get 2 nitrogens, we need to start with 2 NO2, so x = 2:

2 NO2 + H2O + y O2 ====> 2 HNO3

In order to end up with only 6 oxygens, therefore, we need only ½ mole of oxygen gas, thus y = ½, so the balanced equation becomes:

2 NO2 + H2O + ½ O2 ===> 2 HNO3

Answer 2

4NO2 + O2 + 2H2O ----> 4HNO3