The document defines limiting reactants as the reactant that is used up first in a chemical reaction and limits the amount of product that can be formed. The limiting reactant determines how many reactions can take place and how much of the excess reactant will be left over after the reaction stops due to the limiting reactant running out. Examples are provided to demonstrate identifying the limiting and excess reactants given the amounts of reactants available.

1. Limiting Reactants
Unit 8: Stoichiometry

2. • 4 Legs + 1 Top  1 Table
This is a table…

3. • ONE table
• Why?
–You run out of
table legs!
How many tables can you build with six table legs?

4. • TWO tables
• What do you
run out of
first?
–Table Tops
• What do you
have extra
of?
–Table Legs
How many tables can you build with 2 table tops and 9
legs?

5. • In a chemical reaction, one
reactant may run out before
another…
–You have too many of one thing and
not enough of the other
• The reactant that is not left over
(not in excess) is the limiting
reactant
What are limiting reactants?

6. • The limiting reactant is the
reactant that is not present in
excess
• The limiting reactant will be used
up first
• The limiting reactant therefore
limits the amount of product that
can be formed by the reaction
What are limiting reactants?

7. • LR “limits” or determines the number
of reactions that can take place
• When the LR runs out the reaction
stops!
• LR determines how much product
that can be made
• LR determines how much of the other
reactant is left over
What are limiting reactants?

8. • The excess reactant (XS) is the
reactant that is left over, unused
after the LR runs out and the
reaction stops
What is an excess reactant?

9. • How many batches of cookies can be made
with the ingredients in the pantry?
Practice

10. • Each ingredient has enough to make how many
batches of cookies? Least # of batches = LR
Practice

11. You are in lab and you are making
water from the reaction of hydrogen
gas and oxygen gas. You have 6
moles of hydrogen and 4 moles of
oxygen. What are the limiting and
excess reactants?
Practice

12. 2 H2 + 1 O2 → 2 H2O
How many reactions can be made with 6 mol Hydrogen?
How many reactions can be made with 4 mol Oxygen?
LR?
Practice