The reaction of chlorine gas with solid phosphorus (P4) produces solid phosphorus pentachloride. When 63.5 g chlorine reacts with 28.5 g P4, which reactant is limiting?
Write and balance the equation.
Convert grams given to mols P and mols Cl2.
Convert mols P to mols PCl5.
Convert mols Cl2 to mols PCl5.
The SMALLER number of mols is the correct value for mols PCl5 formed and the reagent providing that number is the limiting reagent.
chloride
To determine which reactant is limiting, we need to compare the amounts of products that can be formed from each reactant. The reactant that produces the smaller amount of product will be the limiting reactant.
To find the limiting reactant, we first need to calculate the number of moles of each reactant. We can use the molar mass of each element to convert the given masses into moles.
1. Calculate the number of moles of chlorine (Cl2):
Number of moles = mass / molar mass
Molar mass of chlorine (Cl2) = 35.45 g/mol
Moles of chlorine = 63.5 g / 35.45 g/mol ≈ 1.79 mol
2. Calculate the number of moles of solid phosphorus (P4):
Number of moles = mass / molar mass
Molar mass of solid phosphorus (P4) = 123.89 g/mol
Moles of solid phosphorus = 28.5 g / 123.89 g/mol ≈ 0.23 mol
3. Next, we need to find the stoichiometric ratio between chlorine and solid phosphorus in the balanced chemical equation. The balanced equation is:
P4 + 10Cl2 → 4PCl5
According to the equation, 1 mole of solid phosphorus reacts with 10 moles of chlorine to produce 4 moles of solid phosphorus pentachloride.
4. Calculate the number of moles of chlorine required to react with the number of moles of solid phosphorus:
Moles of chlorine required = 10 × moles of solid phosphorus
Moles of chlorine required = 10 × 0.23 mol = 2.3 mol
Comparing the amounts of chlorine available (1.79 mol) and chlorine required (2.3 mol), we can see that the chlorine is the limiting reactant. Therefore, chlorine is the reactant that limits the amount of solid phosphorus pentachloride that can be produced.
Note: If the number of moles of the limiting reactant (in this case, chlorine) was less than the number of moles of solid phosphorus pentachloride formed (based on the stoichiometry), we would use the limiting reactant to calculate the amount of product formed.