1. Limiting Reactant
There are MANY different ways to solve Limiting Reactant questions depending on what is asked – this is one way…

2. What was the “limiting reactant?”
How many BLT Sandwiches can you make with 3 Tomatoes, 2 Kg of Bacon, 1 head of lettuce and 4 slices of bread? 2
What was the “limiting reactant?”
How did you identify it?

3. OUTCOME QUESTION(S): C11-3-15 STOICHIOMETRY Excess reactant
Solve stoichiometric problems involving moles, mass, and volume, given the reactants and products in a balanced chemical reaction.
Include: heat of reaction
Identify the limiting reactant and calculate the mass of a product, given reaction equation and reactant data.
Include: theoretical yield, experimental yield
Vocabulary & Concepts 
Excess reactant

4. No more products can be made, regardless of “extra” nitrogen
Limiting Reactant - determines the amount of product that can be formed in a reaction.
N2 (g) H2 (g)
2 NH3 (g)
2 moles moles N H H N H N N H H
No more products can be made, regardless of “extra” nitrogen
Reactants remaining are called the excess reactants.

5. How to Solve Limiting Reactant Problems
Step 1: Record what you HAVE
Step 2: Calculate what you will USE
Pick one reactant and calculate how much of the other you will use.
Step 3: Identify the limiting reactant
Ask “Do I have enough?”
Step 4: Use limiting reactant to determine the amount of product
Don’t panic!
The calculations are just more of the same stoichiometry

6. Pick EITHER reactant and calculate the other
How much NaCl is produced when 6.70 mol of Na react with 3.20 mol of Cl2?
6.70 mol
3.20 mol
2 Na (s) + Cl2 (g) NaCl (s)
HAVE
USE
Pick EITHER reactant and calculate the other
6.70 mol Na
1 Cl2 =
3.35 mol
3.35 mol
Cl2 (use)
2 Na
Step 1: Record what you HAVE
Step 2: Calculate what you will USE
Pick one reactant and calculate how much of the other you will need.

7. Cl2 is the Limiting Reactant
For comparison: let’s pretend we picked the other reactant…
2 Na (s) + Cl2 (g) NaCl (s)
HAVE mol mol
USE mol
3.20 mol Cl2
2 Na =
6.40 mol
6.40 mol
Na (use)
1 Cl2
Both calculations lead to the SAME conclusion:
Too much Na OR Not enough Cl2
Cl2 is the Limiting Reactant
Step 3: Identify the limiting reactant
Ask “Do I have enough?”

8. Na - excess reactant Cl2 - limiting reactant
2 Na (s) + Cl2 (g) NaCl (s) ?
HAVE mol mol
USE mol mol
3.20 mol Cl2
2 NaCl
= mol NaCl (made)
1 Cl2
So this reaction will use ALL 3.20 moles of Cl2 and only 6.40 moles of Na to make 6.40 moles of NaCl
This is the step most mess up on – be sure to start with the right value (what you HAVE of the Limiting Reactant)
Step 4: Use limiting reactant to determine the amount of product

9. Pick EITHER reactant and calculate the other
How much CO2 is produced with 10 mol of propane and 10 mol of O2 and what is excess is left over?
C3H8 (g) O2 (g) CO2 (g) + H2O (g) 5 3 4
HAVE
10 mol mol
USE
At this point we know the LR (we don’t HAVE enough)  Oxygen
We still don’t know how much excess C3H8 there is…
Pick EITHER reactant and calculate the other
10 mol C3H8
5 O2 =
50 mol
50 mol
O2 (use)
1 C3H8
Step 1: Record what you HAVE
Step 2: Calculate what you will USE
Pick one reactant and calculate how much of the other you will need.
Step 3: Identify the limiting reactant
Ask “Do I have enough?”

10. C3H8 - excess reactant O2 - limiting reactant
C3H8 (g) O2 (g) CO2 (g) + H2O (g) 5 3 4
HAVE mol mol -
USE mol ?
8 mol (excess)
We have to go the “other way” too – to find what is left over
10 mol O2
1 C3H8
= 2 mol
2 mol
C3H8 (use)
5 O2
NOTE: Finding the excess left over requires the HAVE and USE for the excess reactant – this might have already been done IF you were lucky enough to pick the right reactant to start with in step 2…

11. C3H8 - excess reactant O2 - limiting reactant
C3H8 (g) O2 (g) CO2 (g) + H2O (g) 5 3 4 ?
HAVE mol mol -
USE mol mol
8 mol (excess)
10 mol O2
3 CO2
= 6 mol CO2 (made)
5 O2
So this reaction will use ALL 10 moles of O2 and only
2 moles of C3H8 to make 6 moles of CO2
Unless asked, the other “USE” value – C3H8 - isn’t necessary to finding the product, only for finding the excess
Step 4: Use limiting reactant to determine the amount of product

12. 3 2 N2 (g) + H2 (g) NH3 (g) = 16.3 g N2 (use) = 3.90 g H2 (use)
How many grams of ammonia are made from 3.50 g of H2 gas and 18.0 g of nitrogen gas? What’s left?
N2 (g) H2 (g) NH3 (g) 3 2
HAVE g g
N2 = 28.0 g/mol
USE
16.3 g
3.90 g
H2 = 2.0 g/mol
3.50 g H2
1 mol H2
1 N2
28.0 g N2
= g N2 (use)
2.0 g H2
3 H2
1 mole N2
Did you “pick” right? IF so, only one of these calculations was necessary!
18.0 g N2
1 mol N2
3 H2
2.0 g H2
= g H2 (use)
1 mole H2
28.0 g N2
1 N2

13. N2 - excess reactant H2 - limiting reactant
N2 (g) H2 (g) NH3 (g) 3 2
HAVE g g ? -
USE
16.3 g
3.90 g
1.7 g (excess)
N2 - excess reactant H2 - limiting reactant
NH3 = 17.0 g/mol
3.50 g H2
1 mol H2
2 NH3
17.0 g NH3
= 19.8 g NH3 (made)
2.0 g H2
3 H2
1 mole NH3
Step 3: Identify the limiting reactant
Ask “Do I have enough?”
Step 4: Use limiting reactant to determine the amount of product

14. 5 3 4 C3H8 (g) + O2 (g) CO2 (g) + H2O (g)
What volume of CO2 is formed by the reaction of 75.0 g of propane and L of oxygen at STP?
C3H8 (g) O2 (g) CO2 (g) + H2O (g) 5 3 4
HAVE g L
USE
58.9 g
191 L
C3H3 = 44.0 g/mol
75 g C3H8
1 mol C3H8
5 mol O2
22.4 L O2
= 191 L O2
44 g C3H8
1 mol C3H8
1 mol O2
Did you “pick” right?
150 L O2
1 mol O2
1 mol C3H8
44 g C3H8
= 58.9 g C3H8
22.4 L O2
5 mol O2
1 mol C3H8

15. - 5 3 4 C3H8 (g) + O2 (g) CO2 (g) + H2O (g)?
HAVE g L -
USE
58.9 g
191 L
16.1 g (excess)
C3H8 - excess reactant O2 - limiting reactant
150 L O2
1 mol O2
3 mol CO2
22.4 L CO2
= 90 L CO2
22.4 L O2
5 mol O2
1 mol CO2
So this reaction will use ALL 150 L of O2 and only
58.9 g of C3H8 to make 90 L of CO2
Step 3: Identify the limiting reactant
Ask “Do I have enough?”
Step 4: Use limiting reactant to determine the amount of product

16. C11-3-15 STOICHIOMETRY Excess reactant CAN YOU / HAVE YOU?
Solve stoichiometric problems involving moles, mass, and volume, given the reactants and products in a balanced chemical reaction.
Include: heat of reaction
Identify the limiting reactant and calculate the mass of a product, given reaction equation and reactant data.
Include: theoretical yield, experimental yield
Vocabulary & Concepts 
Excess reactant