Unit VI: Stoichiometry

4. Stoichiometry of Excess Quantities

Excess and Limiting Reactant Calculations

Excess Reactant Too much to react with the other reactant

Excess and Limiting Reactant Calculations

Limiting Reactant not enough limits the amount of product

Find the Limiting and Excess Reactants

LIMITINGLIMITINGREACTANTREACTANT

EXCESSEXCESSREACTANTREACTANT

Find the Limiting and Excess Reactants

You are baking cakes with the Swedish Chef

For 1 Cake You need: 2 cups flour; 3 eggs; 1 pound of butter; 1

cup of milk You have 18 cups of flour; 15 eggs; 6

pounds of butter; 8 cups of milk

Ca + Br2 CaBr2

If 80.2 g of Ca is mixed with 475.2 g of Br2, which reactant is INXS?

Step 1 Covert to moles

Ca + Br2 CaBr2

If 80.2 g of Ca is mixed with 475.2 g of Br2, which reactant is INXS?

Step 1 Covert to moles

Ca + Br2 CaBr2

If 80.2 g of Ca is mixed with 475.2 g of Br2, which reactant is INXS?

Step 2 Revisit Equation

2Al +3Cl2 2AlCl3

If 108.0 g of Al is mixed with 400 g of Cl2 which reactant is in excess?

Directions:

3. Whichever reactant gives you the larger mass of the product is the excess reactant

4. The reactant which is not in excess is the limiting reactant

2Al +3Cl2 2AlCl3

If 108.0 g of Al is mixed with 400 g of Cl2 which reactant is in excess?

Directions:

1. Pick a product

2. Calculate the mass of this product starting with each reactant

(one from 108.0g Al)

(one from 400.0g Cl2)

2Al +3Cl2 2AlCl3

If 108.0 g of Al is mixed with 400 g of Cl2 which reactant is in excess?

2Al +3Cl2 2AlCl3

If 108.0 g of Al is mixed with 400 g of Cl2 which reactant is in excess?

2Al +3Cl2 2AlCl3

Which mass of AlCl3 is actually formed?

2C2H6 + 7O2 4CO2 + 6H2O

a. When 108.0 g of C2H6 is mixed with 360.8 g of O2 which reactant is in excess?

b. What volume of CO2 is produced at STP?

c. What mass of water is produced?

d. What mass of the excess reactant is actually reacted?

e. What mass of the excess reactant is left over?

2C2H6 + 7O2 4CO2 + 6H2O

a. When 108.0 g of C2H6 is mixed with 360.8 g of O2 which reactant is in excess?

Start with C2H6

2C2H6 + 7O2 4CO2 + 6H2O

a. When 108.0 g of C2H6 is mixed with 360.8 g of O2 which reactant is in excess?

Start with O2

2C2H6 + 7O2 4CO2 + 6H2O

b. What volume of CO2 is produced at STP?

Start with LR (O2)

2C2H6 + 7O2 4CO2 + 6H2O

c. What mass of water is produced?

2C2H6 + 7O2 4CO2 + 6H2O

d. What mass of the excess reactant is actually reacted?

2C2H6 + 7O2 4CO2 + 6H2O

e. What mass of the excess reactant is left over?

Hebden

Do Exercises 26-28 on page 133