Convert 98.7 g Sb2S3 to mols. Convert mols Sb2S3 to mols Sb4O6 using the coefficients in the balanced equation. Convert mols Sb4O6 to grams Sb4O6. (This is the theoretical yield.) Convert grams Sb4O6 to percent Sb4O6. %Sb4O6 = [72.4/theoretical yield]*100