1. STOICHIOMETRY
Mass-Mass Problems

2. Write a Balanced Equation
Mass-Mass Problems
STEP 1
Write a Balanced Equation
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3. Determine the Given and the Unknown
Mass-Mass Problems
STEP 2
Determine the Given and the Unknown
Convert Given to Moles

4. Determine the Mole Ratio using the Equation
Mass-Mass Problems
STEP 3
Determine the Mole Ratio using the Equation

5. Determine the Mole Ratio using the Equation
Mass-Mass Problems
STEP 3
Determine the Mole Ratio using the Equation

6. Using Molar mass convert Unknown moles back to Grams
Mass-Mass Problems
STEP 4
Using Molar mass convert Unknown moles back to Grams

7. Mass-Mass Problems
The Steps to solve mass –mass problems will always follow this factor-label guideline.
Given in grams
1 Mole of Given
(Coefficient) Moles Unknown
Molar Mass of Unknown 1
Molar mass of Given
(Coefficient) Moles Given
1 Mole of
Unknown

8. Limiting Reactant
You work in a bakery and your boss says that she wants you to bake as many cakes as you can. You have a 100 pound bag of sugar and a 100 pound bag of flour. Which ingredient will you run out of first?
What if you knew that one cake requires 245 g of sugar and 283 g of flour. Which ingredient will you run out of first?
Flour. That is going to limit the number of cakes you can make. Will you have sugar left over? it will be the excess reactant

9. Limiting Reactant
You have a brand new jar of peanut butter and a new jar of grape jelly and 9 slices of bread How many of my son’s favorite sandwiches can you make?
4.5
What limits the number of sandwiches?
The slices of bread
Bread is the limiting reactant.
Peanut butter and jelly are both in excess.

10. A limiting reactant is the reactant that limits the amount of the other reactants that can combine, and the amount of products formed in a chemical reaction.
The excess reactant is the substance that is not used up completely in a reaction.

11. There are 50 people in excess.
Limiting Reactant
Other examples:
Four hundred people want to take a flight. The plane has only 350 seats available. Only 350 people can go on the flight.
The number of seats on the airplane limits the number of people that can travel.
There are 50 people in excess.

12. Limiting Reactant
Its February, Alex is going to pass out Valentine cards. He goes through his valentines and discards the ones that don’t have Sponge Bob or ____________ on them. He now has only 12 acceptable valentines. He knows he’ll get a kiss from each girl that receives an acceptable valentine. But there are 15 girls in his class.
Limiting reactant: acceptable valentines Excess reactant: girls
The product: The KISSES are limited to 12

13. How about the game of musical Chairs??
Limiting Reactant
How about the game of musical Chairs?? :
the limiting reactant is the chairs
the players are in excess.

14. Limiting Reactant
Real Life How many times do you breathe in one minute? Let’s count.
Did you know that the average person exhales 20 moles of carbon dioxide in a day. How many grams is this?
20 moles CO2 | g CO2 = 880 g CO2
| 1 mol CO2

15. Limiting Reactant
Do we ever need to worry about the amount of CO2 that we exhale? Why not?
What if we were in a contained atmosphere? Prolonged exposure of humans to concentrations of 5 % CO2 may cause unconsciousness and death.
How do we remove CO2 from the air?
React it with lithium hydroxide.

16. Given: 20 moles CO2 Unknown: grams of LiOH
2 LiOH + CO2  Li2CO3 + H2O
How much LiOH is needed to remove the CO2 from the atmosphere for one person for one day?
Given: 20 moles CO Unknown: grams of LiOH
20 moles CO2 | 2 mole LiOH | g LiOH = 960 grams LiOH
| 1 mole CO2 | 1 mole LiOH
Who might need this information?
CO2 Launch

17. On the Lunar Module there was:
Apollo 13 space flight there were two compartments to capsule, the service station compartment blew up and the 3 astronauts had to remain in the Lunar Module. Carbon dioxide levels were rising. Did they have enough LiOH to absorb the carbon dioxide produced by 3 people?
On the Lunar Module there was:
“5 filters to last 2 people for 1.5 days”
How much LiOH does 1 filter contain?
1 filter | 2 people | 960 g LiOH | 1.5 days = 576 grams LiOH
| 5 filters | 1 person
So LiOH would have been the limiting reactant and CO2 would have been the excess reactant.

18. Stoichiometry Overview
Click on the following page and then go to section 4.8 Limiting Reactants.
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