Excess/limiting quantities

i have no idea how to do excess and limiting (mole conversions) does this concept even apply to this Question and how to figure out this out?
if 10 g of ammonia gas reacted with 5 g of Oxygen gas, what mass of water is produced? using this eqn: NH3 + O2 --> NO2 + H2O

whozum

Figure out how many moles of each substance you have (molar masses).
Then look at your stoichiometric ratios, your equation tells you for every mole of ammonia, one mole of oxygen gas will react. This is given directly from the coefficients of each of the reactants.

If you have X moles of oxygen gas and Y moles of ammonia, then what is the maximum amount you can react if X < Y? Highlight for answer:
X moles, because once you've used up X moles, you have some Y moles left over that have nothing to react with.

Be careful when calculating the mass of oxygen.

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