Question

For the reaction, 2.72 moles of Fe were mixed with 3.50 moles of Cl2 to give FeCl3. It was determined that the Cl2 was the limiting reactant. How many moles of Fe remained unreacted at the end of the reaction?

Answer 1

The balanced equation:
2Fe(s)+3Cl2(g)=2FeCl3(s)

Answer 2

use the mole ratio of iron to chlorine as a conversion fraction and convert the moles of chlorine into moles of iron

Answer 3

Since you know what your limiting reactant is start with that.

Convert grams of limiting reactant (LR) to moles of LR using molar mass(from the periodic table)

Covert moles of LR to moles of PRODUCT (what you're looking for) using molar ratio (the coefficients from the balanced equation)

Convert moles of product to grams of product using molar mass,

And since you calculated this using your LR you know that this is the most amount of product that can be created given your reactants.

Does that make sense?