1. Write the Balanced Chemical Equation:

Fe + S → FeS

2. Convert Grams to Moles:

* For Fe:

* Moles of Fe = (25.0 g Fe) / (55.845 g/mol Fe) = 0.447 mol Fe

* For S:

* Moles of S = (32.0 g S) / (32.065 g/mol S) = 0.998 mol S

3. Determine the Limiting Reactant:

* The limiting reactant is the one that gets completely consumed first, determining the maximum amount of product formed.

* From the balanced equation, the mole ratio of Fe to S is 1:1.

* Since we have less moles of Fe (0.447 mol) than S (0.998 mol), Fe is the limiting reactant.

4. Calculate the Theoretical Yield of FeS:

* The mole ratio of Fe to FeS is also 1:1.

* Therefore, the theoretical yield of FeS is equal to the moles of Fe: 0.447 mol FeS.

5. Convert Moles to Grams:

* Theoretical yield of FeS in grams = (0.447 mol FeS) * (87.91 g/mol FeS) = 39.3 g FeS

Therefore, the theoretical yield of FeS if 25.0 g Fe and 32.0 g S react is 39.3 g FeS.