how many grams of hydrogen are necessary to react completely with 50.0 g of nitrogen in the reaction N2+3H2 = 2NH3

Question

N₂ + 3H₂ → 2NH₃

Answer 1

Molar mass of N:  14.0067 g/mol

Molar mass of H:  1.00794 g/mol

Equation is already balanced the way it is written.  So, using dimensional analysis and the balanced equation gives:

 50.0 g N * (1 mol N / 14.0067 g N) * (1 mol N2 / 2 mol N) * (3 mol H2 / 1 mol N2)

* (2 mol H / 1 mol H2) * (1.00794 g/mol H)  =  10.794 g H

Since there are 3 significant figures in the question, we will use 3 significant figures and the answer is:

10.8 g hydrogen

Keep in mind the stoichiometry of the equation allows us to react both of the reactants completely.  If you don't follow the balanced equation, you will have an excess of one of the reactants.