1. The Wisdom of Gallagher
Why are there Interstate Highways in Hawaii?
Why are there floatation devices under plane seats instead of parachutes?
Why do we drive on parkways and park on driveways?
Why do hot dogs come ten to a package and hot dog buns only eight?

2. Limiting Reactants
Percentage Yield

3. Hot Dogs in the News
Takeru Kobayashi of Japan downed 44½ hot dogs in 12 minutes.
One hot dog = one hot dog + one bun.
WHAT IF…
Mr. Kobayashi didn’t do his math correctly. He bought 5 packs of hot dogs (10 per package) and 5 packs of hot dog buns (8 per package). How many hot dogs (according to the official formula) could he have eaten?
Source: CNN.com

4. Hot Dogs in the News Excess 40 possible hot dogs WHAT IF…
One hot dog = one hot dog + one bun.
WHAT IF…
Mr. Kobayashi didn’t do his math correctly. He bought 5 packs of hot dogs (10 per package) and 5 packs of hot dog buns (8 per package). How many hot dogs (according to the official formula) could he have eaten?
Excess
5 hot dog packs
10 hot dogs
50 hot dogs x =
1 hot dog pack
Limiting Factor
40 possible hot dogs
5 bun packs
8 buns
40 buns x =
1 bun pack
Source: CNN.com

5. Let’s Revisit the Cookies (again)…
For 1 batch:
In my pantry, I have:
5.5 cups of flour
16 Tbsp of butter
lots of everything else
2.25 cups flour
8 Tbsp butter
0.5 cups shortening
0.75 cups sugar
0.75 cups brown sugar
1 tsp salt
1 tsp baking soda
1 tsp vanilla
0.5 cups Egg Beaters
12 oz. Chocolate chips
How many batches of cookies can I make?

6. Let’s Revisit the Cookies (again)…
For 1 batch:
How many batches of cookies can I make?
5.5 cups
2.25 cups flour
8 Tbsp butter
0.5 cups shortening
0.75 cups sugar
0.75 cups brown sugar
1 tsp salt
1 tsp baking soda
1 tsp vanilla
0.5 cups Egg Beaters
12 oz. Chocolate chips
16 Tbsp
EXCESS
1 batch cookies
5.5 c flour x =
2.25 c flour
2.4 batches
LIMITING
1 batch cookies
16 Tbsp butter x =
8 Tbsp butter
2.0 batches

7. Now I Want to Bake a Cake! GONE! SOME FLOUR LEFT OVER…
But do I have all the ingredients I need?
How much flour do I have left after baking all those cookies?
SOME FLOUR LEFT OVER…
5.5 c flour x
2.25 c flour
1 batch cookies =
16 Tbsp butter
1 batch
8 Tbsp butter
2.4 batches of cookies
2.0 batches of cookies
GONE!
2.25 cups flour
4.5 cups flour used
2.0 batches x =
1 batch cookies
5.5 cups – 4.5 cups = 1.0 cups left

8. Limiting Reactants
In the laboratory, a reaction is rarely carried out with exactly the required amounts of each reactant. In most cases, one or more of the reactants is present in excess, that is, there is more than the exact amount required to react.
Once one of the reactants is used up, no more product can be formed. The substance that is completely used up first in a reaction is the limiting reactant.

9. The action of a limiting reactant to determine the extent to which a reaction takes place is like producing meals at a cafeteria.
When you run out of chicken pieces, no more chicken dinners can be produced, even though there might be a good supply of mashed potatoes and vegetables…..”the other reactants”.
Leftover!
Not enough!

10. The limiting reactant (reagent) is the reactant that limits the amounts of the other reactants that can combine and the amount of product that can form in a chemical reaction.
The excess reactant is the substance that is not used up completely in a reaction.

11. Limiting Reactants in Chemistry
5.0 moles of chlorine gas react with 5.0 moles of sodium to produce sodium chloride. Which reagent is the limiting reactant? How much of the excess reactant is left over?
Cl2 (g) + 2 Na
NaCl
EXCESS
2 givens = 2 equations!
2 mol NaCl
5.0 mol Cl2 x =
10. mol NaCl
1 mol Cl2
LIMITING
2 mol NaCl
5.0 mol Na x =
5.0 mol NaCl
5.0 mol Cl2 given
2 mol Na
2.5 mol Cl2 used
1 mol Cl2
2.5 mol Cl2
5.0 mol Na x =
2.5 mol Cl2 left
2 mol Na

12. Practice Problems 1. 3 CuSO4 + 2 Al Al2(SO4)3 + 3 Cu
In this reaction, 20.0 g of CuSO4 reacts with 20.0 g of Al. Which reactant is limiting?
How much of the excess reactant is left over?
1 mol CuSO4
3 mol Cu
20.0 g CuSO4 x =
0.125 mol Cu x
g CuSO4
3 mol CuSO4
20.0 g Al
1 mol Al
3 mol Cu
1.11 mol Cu x x =
26.98 g Al
2 mol Al
1 mol CuSO4
2 mol Al
26.98 g Al
20.0 g CuSO4 x x = x
g CuSO4
3 mol CuSO4
1 mol Al
2.25 g Al
20.0 g Al – 2.25 g Al =
17.8 g Al
EXCESS
USED

13. Practice Problems 2. 2 H2 (g) + O2 (g) 2 H2O
In this reaction, 5.0 g of H2 reacts with 5.0 g O2. Which reactant is limiting? How
many grams of H2O are produced?
5.0 g H2 x
1 mol H2
2.02 g H2
2 mol H2O
2 mol H2 =
2.5 mol H2O
5.0 g O2 x
32.00 g O2
1 mol O2
2 mol H2O =
0.31 mol H2O
18.02 g H2O
0.31 mol H2O x =
5.6
g H2O
1 mol H2O
smallest number
of moles

14. On Perfection
“Perfection never exists in reality, but only in our dreams.”
- Dr. Rudolf Dreikurs
“Perfection is our goal, excellence will be tolerated.”
- J. Yahl

15. Get Real!
Johnny took a quiz yesterday. He missed 4 questions and earned 63 points out of 70.
Was he perfect?
What was his possible score?
What was his actual percent score?
70 points = 100 %
90 %

16. Percentage Yield

17. Get Real!
Mrs. Kennedy ran a reaction in her lab yesterday. She predicted that 183 grams of product would be formed. The reaction only yielded 162 grams of product.
Was her reaction perfect?
What was the percent yield?
162 grams
100
88.5 % x =
183 grams
162 grams = actual yield
183 grams = theoretical yield

18. Percentage Yield
The theoretical yield is the maximum amount of product that can be produced from a given amount of reactant.
In most chemical reactions, the amount of product obtained is less than the theoretical yield.
The measured amount of product obtained from a reaction is called the actual yield of the product.
The percent yield is the ratio of the actual yield to the theoretical yield, multiplied by 100.