Balance the equation
8Zn + S8 -----> 8ZnS
work out how much ZnS is possible if all of each reagent were to react. The reagent that produces the least product is the limiting reagent.
moles Zn = mass / molar mass = 4.88 g / 65.38 g/mol = 0.07464 moles
8 moles Zn reacts to form 8 moles ZnS
Therefore moles ZnS possible = moles Zn = 0.07464 moles
moles S8 = 5.03 g / 256.48 g/mol = 0.01961 mol
1 mole S8 reacts to form 8 moles ZnS
Therefore moles ZnS possible = 8 x moles S8 = 0.1569 mol
The amount of Zn provided gives the least ZnS, therefore Zn is the limiting reagent.
The theoretical yield is the maximum possible yield possible from the reagents provided. It is the amount of product that will form if all the limiting reagent reacts.
So in this case 4.88 g Zn yields 0.07464 mol ZnS
theoretical mass ZnS = molar mass x moles
= 97.44 g/mol x 0.07464 mol
= 7.27 g
% yield = actual yield / theoretical yield x 100/1
= 6.02 g / 7.27 g x 100/1
= 82.8 %
