Limiting Reactants

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Limiting Reactants Percent Yield

• Continuation from Stoichiometry

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A. Types of Reactants

• 1. Limiting Reactant
• Limits the amounts in a chemical reaction (the
  other reactant all products)

2. Excess Reactant The substance not used up
in the reaction (more than enough)
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B. Reactants Stoichiometry Problems 4 NH3 5 O2
? 4 NO 6 H2O

• 1. Which is the limiting reactant when 7.50 mol
  NH3 is mixed with 11.0 mol O2?

7.50 mol NH3
5 mol O2

X
4 mol NH3
9.38 mol O2
NH3 is the limiting reactant.
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2. What is the excess reactant? How much of
the excess reactant is left over in moles?

• Oxygen is the excess reactant
• 11.0 mol 9.38 mol 1.62 mol

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3. How much of each product is formed in
moles?
7.50 mol NH3
4 mol NO

X
4 mol NH3
7.50 mol NO
7.50 mol NH3
6 mol H2O

X
4 mol NH3
11.3 mol H2O
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If 20.5 g NH3 react with 20.5 g O2, which is the
limiting reactant? How do you know?
20.5 g NH3
160.0 g O2

X
68.16 g NH3
48.1 g O2
O2 is the limiting reactant because 48.1 g are
needed but there are only 20.5 g available.
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C. Types of Yields of Products

• Theoretical Yieldthe calculated amount that
  should be produced
• Actual Yieldthe measured amount of a product
• Percent Yieldthe efficiency of the reaction
  found from the ratio of the actual yield to the
  theoretical yield x 100 ( A/T x 100)

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D. Yield Stoichiometry Problems 4 NH3 5 O2 ?
4 NO 6 H2O

• When the proper amount of NH3 reacts with enough
  O2, 120.0 g of NO was produced. Tom performed the
  experiment, but actually produced 98.0 g NO. What
  is the yield of NO?

98.0 g NO
X 100

81.7
120.0 g NO
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• 2. When 36.8 g of NH3 react with excess of
  oxygen, the actual yield of water is 56.2 g. What
  is the yield of water?

36.8 g NH3
X
108.1 g H2O

68.16 g NH3
58.4 g H2O
56.2 g H2O
X 100

96.2
58.4 g H2O
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• 3. When 204.8 g of O2 react with excess of NH3,
  the actual yield of water is 75.83 g. What is the
  yield of water?

204.8 g O2
X
108.1 g H2O

160.0 g O2
138.4 g H2O
75.83 g H2O
X 100

54.79
138.4 g H2O