1. LRs in the environment – why are they so important?
Limiting Reactants
LRs in the environment – why are they so important?

2. I’m hungry, let’s talk about food!
Suppose we want to make a grilled cheese sandwich…..
2 Bread Cheese Sandwich

3. So how many sandwiches can we make with…

4. That’s right! Only 5

5. Food for thought… How come we can’t make anymore?
Because the Bread RAN OUT!
Can we say the Bread LIMITS the rxn?
Yep! The Bread is the Limiting Reactant.
How much bread do we have left?
NONE, of course!
What do we have leftover?
Cheese! It’s in excess.
How much cheese is leftover?
5 Slices used so… 8 – 5 = 3 leftover

6. Because we love conversion factors, let’s apply it to what we mentally solved!
2 Bread Cheese Sandwich
10 Bread x 1 Sandwich = 5 Sandwiches
2 Bread
8 Cheese x 1 Sandwich = 8 Sandwiches
1 Cheese

7. Applying Chemistry to Food
Can we make 8 Sandwiches?
Nope! Why not?
Because the Bread RAN OUT!
Bread = Limiting Reactant, all used!
5 Sandwiches = Theoretical Yield, this is the maximum amount we can make.
Limiting Reactant produces the Theoretical Yield
Cheese = Excess Reactant, leftovers!

8. Using your Balanced Rxn as a Recipe
Write a balanced reaction
Convert: mass reactants  moles reactants
Convert: moles reactants  moles product
Convert: moles product  mass product
Limiting Reactant produces the Theoretical Yield of Product!
What’s leftover?
LR = none, all used!
Excess Reactant: calculate how much reacted with LR, then subtract from what you started with
Moles LR  Moles ER  Mass ER; then subtract!

9. Why’s this so important?
What is the Limiting Reactant of all Plant Life?
PHOSPHOROUS
P is “locked up” in phosphoric rocks and is not readily available.
It is Recycled through the Food Chain.
Thus, plant growth is limited because of the need for phosphorous!

10. Years ago…. Phosphorous was added to Soaps & Detergents
It was great for removing hardwater – water with lots of minerals in it.

11. But then there was the Run-Off…
Phosphorus leaked into…
streams,
then rivers,
then lakes

12. ALGAE TAKES OVER !!!!

13. Hyper-Eutrophication

15. Save your Environment Open your eyes & pay attention
Think! Should I really put that in the trash or sink???
Learn everyday
Practice: your chem calculations are really important in the world today!