Your reaction will produce
Start with the balanced chemical equation for the combustion of ammonia
Notice that you have a
Because the pressure and temperature of the reaction are kept constant, you have, using the ideal gas law equation
In this case, regardless of how many cubic centimeters of ammonia you have, you'll always need 3/4 fewer cubic centimeters of oxygen for the reaction to take place.
Since you have
This tells you that ammonia acts as the limiting reagent, i.e. it doesn't allow for all the oxygen to react. As a result, you'll be left with excess oxygen.
In order to determine the volumes of nitrogen gas and of water vapor produced, you use the volume ratios that exist between ammonia and the products.
Therefore, after the reaction is complete, you'll be left with