ii. stoichiometry in the real world (p. 379 – 388) stoichiometry – ch. 11

II. Stoichiometry in the Real World

(p. 379 – 388)

Stoichiometry – Ch. Stoichiometry – Ch. 1111

A. Limiting ReactantsA. Limiting ReactantsA. Limiting ReactantsA. Limiting Reactants

Available IngredientsAvailable Ingredients• 4 slices of bread• 1 jar of peanut butter• 1/2 jar of jelly

Limiting ReactantLimiting Reactant• bread

Excess ReactantsExcess Reactants• peanut butter and jelly

A. Limiting ReactantsA. Limiting ReactantsA. Limiting ReactantsA. Limiting Reactants

Available IngredientsAvailable Ingredients• 24 graham cracker squares• 1 bag of marshmallows• 12 pieces of chocolate

Limiting ReactantLimiting Reactant• chocolate

Excess ReactantsExcess Reactants• Marshmallows and graham

crackers

A. Limiting ReactantsA. Limiting ReactantsA. Limiting ReactantsA. Limiting Reactants

Limiting ReactantLimiting Reactant• one that is used up in a reaction• determines the amount of product that

can be produced

Excess ReactantExcess Reactant• added to ensure that the other reactant

is completely used up• cheaper & easier to recycle

A. Limiting ReactantsA. Limiting ReactantsA. Limiting ReactantsA. Limiting Reactants

1. Write the balanced equation.

2. For each reactant, calculate the

amount of product formed.

3. Smaller answer indicates:

• limiting reactant

• amount of product actually possible

A. Limiting ReactantsA. Limiting ReactantsA. Limiting ReactantsA. Limiting Reactants

79.1 g of zinc react with 68.1 g HCl. Identify the limiting and excess reactants. How many grams of hydrogen can be formed?

Zn + 2HCl ZnCl2 + H2 79.1 g ? g68.1 g

A. Limiting ReactantsA. Limiting ReactantsA. Limiting ReactantsA. Limiting Reactants

79.1g Zn

1 molZn

65.39g Zn

= 2.44 g H2

1 molH2

1 molZn

2.02 gH2

1 molH2

Zn + 2HCl ZnCl2 + H2 79.1 g ? g68.1 g

A. Limiting ReactantsA. Limiting ReactantsA. Limiting ReactantsA. Limiting Reactants

2.02 g H2

1 molH2

68.1g HCl

1 molHCl

36.46 g HCl

= 1.89 g H2

1 molH2

2 molHCl

Zn + 2HCl ZnCl2 + H2 79.1 g ? g68.1 g

A. Limiting ReactantsA. Limiting ReactantsA. Limiting ReactantsA. Limiting Reactants

Zn: 2.44 g H2 HCl: 1.89 g H2

Limiting reactant: HCl

Excess reactant: Zn

Product Formed: 1.89 g H2

left over zinc

A. Limiting Reactants #2A. Limiting Reactants #2A. Limiting Reactants #2A. Limiting Reactants #2

5.42 g of magnesium ribbon react with 4.00 g of oxygen gas. Identify the limiting and excess reactants. How many grams of magnesium oxide are formed?

2Mg + O2 2MgO 5.42 g ? g4.00 g

A. Limiting Reactants #2A. Limiting Reactants #2A. Limiting Reactants #2A. Limiting Reactants #2

5.42g Mg

1 molMg

24.31g Mg

= 8.99 g MgO

2 molMgO

2 molMg

40.31 gMgO

1 molMgO

2Mg + O2 2MgO

5.42 g ? g4.00 g

A. Limiting Reactants #2A. Limiting Reactants #2A. Limiting Reactants #2A. Limiting Reactants #2

40.31g MgO

1 molMgO

4.00g O2

1 molO2

32.00 g O2

= 10.1 g MgO

2 molMgO

1 molO2

2Mg + O2 2MgO

5.42 g ? g4.00 g

A. Limiting Reactants #2A. Limiting Reactants #2A. Limiting Reactants #2A. Limiting Reactants #2

Mg: 8.99 g MgO O2: 10.1 g MgO

Excess oxygen

Limiting reactant: Mg

Excess reactant: O2

Product Formed: 8.99 g MgO

A. Limiting ReactantsA. Limiting ReactantsA. Limiting ReactantsA. Limiting Reactants

What other information could you find in these problems?

• How much of each reactant is used – in grams, liters, moles

• How much of excess reactant is left over – in grams, liters, moles

B. Percent YieldB. Percent YieldB. Percent YieldB. Percent Yield

100yield ltheoretica

yield actualyield %

calculated on paper

measured in lab

B. Percent YieldB. Percent YieldB. Percent YieldB. Percent Yield

When 45.8 g of K2CO3 react with excess

HCl, 46.3 g of KCl are formed. Calculate the theoretical and % yields of KCl.