RPAL Limiting Reagents 2 — Questions and Answers
Question 1: For the reaction 2Al + 3Cl₂ → 2AlCl₃, if 0.6 mol Al and 0.6 mol Cl₂ are used, which is the limiting reagent?
- Cl₂ (Correct answer)
- Al
- AlCl₃
- Both are limiting
Correct answer: Cl₂
The 2:3 ratio means 0.6 mol Al needs 0.9 mol Cl₂; only 0.6 mol Cl₂ is available, so Cl₂ is limiting.
Question 2: A student mixes 5 g of H₂ and 32 g of O₂ for the reaction 2H₂ + O₂ → 2H₂O. What is the limiting reagent?
- O₂ (Correct answer)
- H₂
- H₂O
- Neither
Correct answer: O₂
5 g H₂ = 2.5 mol and 32 g O₂ = 1 mol; the 2:1 ratio requires 1.25 mol O₂ for 2.5 mol H₂, but only 1 mol O₂ is present, making O₂ limiting.
Question 3: Which of the following is NOT a step in identifying the limiting reagent?
- Calculating the percent yield of the reaction (Correct answer)
- Converting mass to moles for each reactant
- Dividing moles by stoichiometric coefficients
- Comparing the resulting ratios
Correct answer: Calculating the percent yield of the reaction
Percent yield is calculated after identifying the limiting reagent; it is not part of the identification process itself.
Question 4: If a reaction uses 10 mol of each reactant and the stoichiometric ratio is 1:1, what is true about the limiting reagent?
- There is no limiting reagent — both are consumed completely (Correct answer)
- The first reactant listed is limiting
- The second reactant listed is limiting
- The product determines which is limiting
Correct answer: There is no limiting reagent — both are consumed completely
When reactants are present in the exact stoichiometric ratio, both are consumed completely and neither is in excess.
Question 5: In a reaction with a 1:2 stoichiometric ratio (A:B), you have 3 mol A and 5 mol B. Which is limiting?
- B (Correct answer)
- A
- Neither
- Both equally
Correct answer: B
3 mol A requires 6 mol B; only 5 mol B is available, so B is the limiting reagent.
Question 6: What quantity can be calculated directly from the moles of the limiting reagent?
- Moles of product formed (Correct answer)
- Moles of excess reagent remaining
- Activation energy of the reaction
- Enthalpy change of the reaction
Correct answer: Moles of product formed
Using the mole ratio from the balanced equation, the moles of limiting reagent directly yield the moles of product formed.
RPAL Limiting Reagents 2
For the reaction 2Al + 3Cl₂ → 2AlCl₃, if 0.6 mol Al and 0.6 mol Cl₂ are used, which is the limiting reagent?