If 20.0 grams of hydrogen and 40.0 grams of nitrigen are combined to form nitrogen trihidride, how many grams of nitrogen trihydride should be formed?
This is a limiting reagent problem. You know that because amounts for BOTH reactants are given. You work two stoichiometry problems for this and take the one that produces the fewer mols.
Write and balance the equation.
2a. Convert g N2 to moles.
b. Convert g H2 to moles.
3a. Convert mols N2 to moles of product using the coefficients in the balanced equation.
3b. Do the same for mols H2.
3c. Both answers (for 3a and 3b) can't be right; the correct answer in limiting reagent problems is ALWAYS the smaller one and the reagent producing that value is the limiting reagent.
4. Using the smaller number of mols, convert to grams. g = moles x molar mas.