In order to do this, one must use the stoichiometric relationship for balanced chemical equations. We start by writing the balanced equation, then determine the molar mass of antimony, lead, and the Sb2S3. From these we can predict the theoretical yield.
2Sb + 3S ---> Sb2S3
From this equation we get the relationship that there is one mole of Sb2S3 for every 2 moles of Sb used up.
From the periodic table we get that the molar mass of antimony is 121.76 g/mole and sulfur is 32.065 g/mole. From these two we can get the molar mass of the product: 2(121.76g/mol)+3(32.065g/mol) = 339.715 g/mol
The stategy to solve the problem from here is to convert the mass of antimony to moles of antimony using its molar mass, then convert consumed moles of antimony to produced moles of product using the coefficients from the balanced chemical equation, and finally to convert the moles of product to grams of product by using its molar mass.
5.00gSbX(1mole/121.76g) = 0.0412mol Sb
0.0412molSbX(1mole Sb2S3/2moleSb) = 0.0206molSb2S3
0.0206molSb2S3(339.715g/mol)= 6.98 grams of Sb2S3