RPAL Limiting Reagents 2

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?

Accepted Answer

Cl₂

Answer

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?

Accepted Answer

O₂

Answer

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?

Accepted Answer

Calculating the percent yield of the reaction

Answer

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?

Accepted Answer

There is no limiting reagent — both are consumed completely

Answer

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?

Accepted Answer

B

Answer

3 mol A requires 6 mol B; only 5 mol B is available, so B is the limiting reagent.

RPAL - Reactants, Products, and Leftovers Practice Test