AP chem question

Question

How many moles of magnesium oxide are produced by the reaction of 3.82 g of magnesium nitride with 7.73g of water?

Mg3N2 + 3H2O -> 2NH3 + 3MgO

a) 0.114

b) 0.0378

c) 0.429

d) 0.0756

e) 4.57

can someone explain to me how to do this problem? thanks.

Answer 1

Mg₃N₂ + 3H₂O -> 2NH₃ + 3MgO ... balanced equation

Find limiting reactant. Easy way to do it is to divide mols of each reactant by the corresponding coefficient in the balanced equation and see which is less.

Mg₃N₂ : 3.82 g x 1 mol / 100.9 g =0.0379 mols (÷1 -> 0.0379)

H2O : 7.73 g H2O x 1 mol / 18 g = 0.429 mols (÷3 -> 0.143)

Mg₃N₂ is limiting as 0.0379 is less than 0.143. Mg₃N₂ will determine theoretical yield.

Theoretical yield of MgO:

0.0379 mols Mg₃N₂ x 3 mols MgO / 1 mol Mg₃N₂ x 40.3 g MgO/mol = 4.57 g MgO