RPAL Excess Reagents 2

Question 1

In N₂ + 3H₂ → 2NH₃, you start with 2 mol N₂ and 3 mol H₂. After the reaction, how many moles of excess reagent remain?

Accepted Answer

N₂; 1 mol remains

Answer

H₂ is limiting (3 mol H₂ can only react with 1 mol N₂), leaving 2 − 1 = 1 mol N₂ as excess.

Question 2

What units are used when reporting the amount of excess reagent remaining?

Accepted Answer

Moles or grams (depending on the question)

Answer

Excess reagent can be reported in moles or converted to grams using molar mass, depending on what the problem asks for.

Question 3

Why is it useful to calculate the amount of excess reagent remaining?

Accepted Answer

To know what leftover materials are present after the reaction

Answer

Knowing the excess reagent leftover helps in planning reactions, recycling materials, and understanding reaction completeness.

Question 4

For 2Fe + 3Cl₂ → 2FeCl₃, if 4 mol Fe and 3 mol Cl₂ react, how many moles of excess Fe remain?

Accepted Answer

2 mol Fe

Answer

3 mol Cl₂ can react with only 2 mol Fe (from the 2:3 ratio), so 4 − 2 = 2 mol Fe remain as excess.

Question 5

A student reports that after a reaction, 0.5 mol of the excess reagent remains. What does this tell you about the reaction?

Accepted Answer

The reaction went to completion with the limiting reagent fully consumed

Answer

Leftover excess reagent confirms the reaction went to completion and the limiting reagent was fully used up.

RPAL - Reactants, Products, and Leftovers Practice Test