In an experiment of hydrogen reacts with 110.0 g nitrogen gas, producing 100.1 g ammonia.
a) How many grams of nitrogen will be left over?
N2 + 3H2 ==> 2NH3
mols NH3 = grams/molar mass = approx 6 mols but that's an estimate and you should get a better number than that.
Now convert mols NH3 to mols N2. That's approx 6 mols NH3 x (1 mol N2/2 mol NH3) = approx 6*1/2 = approx 3.
Then g N2 used = mols x molar mass = approx 80g.
You started with 110g and used about 80 so have approx 110-80 = ? remaining.