CHEMISTRY COMMUNITY

In class we did an example with NO2 formation:

N2 + O2 --> 2NO
2NO + O2 --> 2NO2
----------------------
N2 + 2O2 --> 2NO2

The way we got the third and final reaction was by adding the first two and the 2NO's "canceled out."
I don't really understand how the 2NO's canceled out but the O2's did not. Why did only the 2NO's get canceled out in order to get the final equation?

The 2NOs cancel out because one is a reactant and the other is a product. The O2s do not cancel out since they are both reactants, and thus they are added together.

the 2NO's are on opposite sides of the equation and therefore will cancel out. however, the O2's are on the same side, so you add them together.

You can only cancel things out when you have the same compound on the reactants side and the products side.