fe +S=FeS
1mol de fe react cu 1 mol de S
56 g fe.................32 g sulf
21000g fe ..........................x g sulf
x=12000g =12 kg
in exces ai S 24 kg-12 kg=12 kg
se produc 56g Fe------------------88 g FeS
21000g Fe...............Y g
Y=33000g=33 kg FeS