20 gram Ca and 64 gram Br reacts to form CaBr2. How many grams of CaBr2 form if 20% of Ca remains at the end of the reaction?

Mass of CaBr₂ : 80 g

Reaction

Ca+2Br⇒CaBr₂

mass of Ca = 20 g

mol of Ca (MW=40 g/mol):

mass of Br = 64 g

mol Br(80 g/mol) :

Ca remains at the end of the reaction⇒ Ca as an excess reactant

20% Ca remains(unreacted) :

Ca reacted :

mol Ca reacted :

mol CaBr₂ = mol Ca reacted = 0.4

mass CaBr₂ (MW=200 g/mol) produced :

Or you can use mol ratio from equation :

mol  CaBr₂ : mol Br (as limiting reactant) = 1 : 2, so mol CaBr₂ :

mass CaBr₂ (MW=200 g/mol) produced :