RPAL Excess Reagents 3

Question 1

In CH₄ + 2O₂ → CO₂ + 2H₂O, if 3 mol CH₄ and 8 mol O₂ react, how many moles of O₂ remain?

Accepted Answer

2 mol

Answer

3 mol CH₄ requires 6 mol O₂; 8 − 6 = 2 mol O₂ remain as excess.

Question 2

When converting excess reagent from moles to grams, which formula is used?

Accepted Answer

Mass = moles × molar mass

Answer

Multiplying the moles of excess reagent by its molar mass gives the mass in grams.

Question 3

For the reaction 2HCl + Ca → CaCl₂ + H₂, if 4 mol HCl and 3 mol Ca are used, what is the excess reagent and how much remains?

Accepted Answer

Ca; 1 mol remains

Answer

4 mol HCl reacts with 2 mol Ca (2:1 ratio), leaving 3 − 2 = 1 mol Ca as excess.

Question 4

In an RPAL table, the 'leftover' row reports which value?

Accepted Answer

The moles of excess reagent remaining after the reaction

Answer

The leftover row in an RPAL table shows the unreacted amount of each substance after the reaction has gone to completion.

Question 5

Which scenario results in the largest amount of excess reagent remaining?

Accepted Answer

Starting with a large surplus of one reactant relative to the stoichiometric requirement

Answer

The greater the surplus of one reactant relative to the stoichiometric need, the more excess remains after the reaction.

RPAL - Reactants, Products, and Leftovers Practice Test