8 Zn + S8 --> 8 ZnS

Question

if 5.00 g of zinc and 3.00g of S8 are available what is ZnS mass?

Answer 1

This is a limiting reagent problem (LR). You know that when amounts are given for more than one of the reactants.
Step 1. Write and balance the equation. You've done that.
Step 2. Determine if Zn or S8 is the LR. There is a short way and a long way. I'll show you the long way.
2. Determine moles each reactant. I will round numbers so you may want to go back and recalculate more accurately.
2a. moles Zn = grams atomic mass = 5.00/about 65 = 0.077
2b. moles S8 = 3.00/256 = 0.012
3. Calculate moles of the product formed for EACH reactant.
3a. First Zn. 0.077 mols Zn x (8 moles ZnS/8 moles Zn) = 0.077 x 1 = 0.077
3b. next S8. 0.012 moles S8 x (8 moles ZnS/1 mol S8) = 0.012 x 8 = 0.096
3c. Identify the LR which is Zn since that produces the smaller of the two reactants.
4. Convert mols Zn to grams. 0.077 x molar mass ZnS = 0.077 x 97 = 7.5 g.
Remember that I have rounded so that 7.5 g is approximate.