RPAL Limiting Reagents

Question 1

What is a limiting reagent in a chemical reaction?

Accepted Answer

The reactant that is completely consumed and stops the reaction

Answer

The limiting reagent is the reactant that runs out first, thereby determining the maximum amount of product that can be formed.

Question 2

In the reaction 2H₂ + O₂ → 2H₂O, if you have 4 mol H₂ and 1 mol O₂, which is the limiting reagent?

Accepted Answer

O₂

Answer

The reaction requires 2:1 ratio of H₂ to O₂, so 4 mol H₂ needs 2 mol O₂, but only 1 mol O₂ is available, making O₂ the limiting reagent.

Question 3

How do you identify the limiting reagent when given masses of two reactants?

Accepted Answer

Convert masses to moles, divide by coefficients, and pick the smallest result

Answer

Converting each reactant's mass to moles and dividing by its stoichiometric coefficient gives a comparable ratio — the smallest value indicates the limiting reagent.

Question 4

If the limiting reagent is fully consumed, what happens to the excess reagent?

Accepted Answer

Some of it remains unreacted (leftover)

Answer

Once the limiting reagent is used up, the reaction stops and the excess reagent remains partially unreacted as leftover.

Question 5

In the reaction N₂ + 3H₂ → 2NH₃, if 1 mol N₂ and 2 mol H₂ are mixed, which is the limiting reagent?

Accepted Answer

H₂

Answer

1 mol N₂ requires 3 mol H₂, but only 2 mol H₂ is available, so H₂ is the limiting reagent.

RPAL - Reactants, Products, and Leftovers Practice Test

RPAL - Reactants, Products, and Leftovers Practice Test

RPAL Limiting Reagents