moles Li3N = 98.7 g/34.8297 g/mol=2.83
the ratio between Li3N and H2O is 1 : 3
moles water neeeded = 2.83 x 3=8.49
mass water = 8.49 mol x 18.02 g/mol=153.0 g
moles NH3 produced = 2.83
molescules of NH3 = 2.83 x 6.02 x 10^23=1.70 x 10^24
moles NH3 (STP) = 45.0/22.4 =2.0
moles Li3N = 2.0
mass Li3N = 2.0 x 34.8297 g/mol=69.6 g