RPAL Excess Reagents

Question 1

What is an excess reagent?

Accepted Answer

A reactant present in greater amount than needed to react with the limiting reagent

Answer

An excess reagent is any reactant that remains after the limiting reagent is completely consumed.

Question 2

How is the amount of excess reagent remaining calculated?

Accepted Answer

Subtract the moles consumed (based on limiting reagent) from the initial moles

Answer

Using stoichiometry, calculate how much excess reagent reacted with the limiting reagent, then subtract from the starting amount.

Question 3

In 2H₂ + O₂ → 2H₂O, if 6 mol H₂ and 2 mol O₂ react, which is the excess reagent and how much remains?

Accepted Answer

H₂; 2 mol remain

Answer

2 mol O₂ consumes 4 mol H₂ (from the 2:1 ratio), leaving 6 − 4 = 2 mol H₂ unreacted.

Question 4

If you increase the amount of excess reagent in a reaction, what happens to the amount of product formed?

Accepted Answer

Nothing — product amount depends only on the limiting reagent

Answer

Since the limiting reagent controls product formation, adding more excess reagent does not change the yield.

Question 5

Which of the following best describes 'leftover' in the RPAL context?

Accepted Answer

The unreacted excess reagent remaining after the reaction stops

Answer

In RPAL problems, 'leftover' specifically refers to the amount of excess reagent that does not react because the limiting reagent runs out.

RPAL - Reactants, Products, and Leftovers Practice Test