1. How much can I make? Maximizing Chemical Quantities
Limiting and Excess Reactants
Percent Yield

2. What is a limiting reactant?
Limiting Reactant - reactant in a chemical reaction that limits the amount of product that can be formed
The reaction will stop once all of the limiting reactant is consumed.

3. What is an excess reactant?
Excess Reactant - reactant in a chemical reaction that remains when a reaction stops
The excess reactant remains because there is nothing to react with it!

4. How many cars can be made?
No matter how many tires there are, if there are only 8 car bodies, then only 8 cars can be made. 

5. Example #1:
Copper metal reacts with sulfur to form copper (I) sulfide according to the balanced equation.
_____ Cu + ____ S  _____ Cu2S
What is the limiting reactant when 80 g Cu reacts with 25 g S?
80 g Cu x _________ = mol of Cu
25 g of S x _______ = mol of S 2 1 1
1.26
1 mol Cu
63.5 g Cu
1 mol S
1.09
32.1 g S

6. Example #1: 2 Cu S  1 Cu2S
What is the mole ratio of Cu to ? ____ Cu : ____ S
mol of Cu x ___________ = mol of S
Translation:
I only need mol of S to fully react with copper.
But I was given ________ mol of S.
Excess = Sulfur Limiting = Copper 2 1
1.26
1 mol S
0.63
2 mol Cu
0.63
1.09

7. What’s the max amount of product that I can yield?
Use Stoichiometry to determine the max amount of product that can be formed.
1.26 mol Cu x _______ x ________ =
1 mol Cu2S
159.1 g Cu2S
100 g Cu2S
2 mol Cu
1 mol Cu2S

8. Theoretically vs. Actually

9. Percent Yield
Theoretical Yield = maximum amount of product that could be formed from a given amount of reactants
Actual Yield = amount actually formed when a reaction is carried out

10. Why don’t reactions always go to completion?
purity of reactants
loss of product formed during filtration
competing reactions
measurement error

11. Theoretical Yield Example
What is the theoretical yield of CaO if 24.8 g of CaCO3 is heated?
_____ CaCO3  _____ CaO + ______ CO2
24. 8 g CaCO3 x ________ x _________ x ________ = g CaO
Theoretical Yield = 13.9 g CaO
1 mol CaCO3
1 mol CaO
56 g CaO
100.1 g CaCO3
1 mol CaCO3
1 mol CaO

12. Percent Yield Example
What is the percent yield if 13.1 g of CaO was actually produced when 24.8 g of CaCO3 was heated?
% Yield= g x 100 = %
13.9 g