1. Limiting Reactants and % Yield

2. Limiting Factors
Limiting factors are those factors which control the speed or the outcome of a reaction or a situation
Ingredients for making “S’mores”:
2 graham crackers
1 marshmallow
1 Hershey bar
How many “S’mores” can you make with 14 graham crackers, 5 marshmallows, and 6 Hershey bars?
How many of each ingredient are left over?
5 “S’mores”, 0 marshmallows, 4 graham crackers, 1 Hershey bar

3. Limiting Reactant Excess
The limiting reactant is the reactant which controls the rate of reaction or the amount of product that can be made
The reactant that you have more than you need to perform a chemical reaction

4. Here’s an example
You are making ham and cheese sandwiches and you have:
5 pieces of ham
5 pieces of cheese
8 pieces of bread
Which of these ingredients do you have more than enough of (excess reactant)?
Which of these do you not have enough of (limiting reactant?

5. Now lets apply this to an equation…
C3H8 + O2  CO2 + H2O
Balance the equation
How many moles of CO2 are produced from 14.8 g of C3H8?
How many moles of CO2 are produced from 3.44 g of O2?
If you mixed 14.8 g C3H8 with 3.44 g O2 , which would run out first? (In other words, which one is the limiting reagent?). How do you know?
Compare using mole ratio

6. Yield Yield is how much product that you produce
Actual yield refers to the amount of product that is actually generated (measured)
Theoretical yield refers to the amount of product that you expect to generate (Calculated)

7. Theoretical vs. Actual Yield
You recently bought a new car. The EPA sticker says that you should get 28 mpg in “average driving”.
Your actual miles per gallon turns out to be less than 28 mpg.
Why?

8. Theoretical Yield vs. Actual
You perform a mass- mass calculation to determine how much chemical should be produced in a reaction.
The actual results of the experiment produce less chemical than calculated.
Why?

9. Calculating Percent Yield
Calculate the theoretical yield (mass-mass calculation).
Determine the actual yield.
Calculate the % yield
% Yield = Actual yield x 100
Theoretical yield

10. A Percent Yield Problem
C3H8 + O2  CO2 + H2O
In an ideal situation, how many grams of CO2 would be produced? (This is the theoretical yield).
If this reaction was carried out and 2.0 g of CO2 were produced (This is the actual yield), what is the percent yield of CO2?