Chapter 9-Stoichiometry

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Chapter 9-Stoichiometry

• Stoichiometry measures and calculates
  amounts of chemicals in a reaction.
• Mole/Mole Problems
• Coefficients
• Show of molecules in equations
• Show of moles in equations

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Example

• Glucose reacts with oxygen to produce carbon
  dioxide and water vapor in cellular respiration.
• a. Write a balanced equation for this reaction.
• b.If 0.30 moles of glucose are reacted, how
  many moles of carbon dioxide will be produced?

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• c. If 0.15 moles of glucose are reacted, how
• many moles of oxygen are reacted?
• d. If 0.26 moles of water are produced, how
• many moles of glucose are reacted?

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• B. Mass Stoichiometry Problems
• First-Write a Balanced Equation
• 1. Change to Moles
• 2. Use Coefficients (Mole Ratios)
• changes chemical
• 3. Change to what is asked for
• May not need steps 1 or 3 depends on what you
  are given and what is asked for.

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• Examples
• 1. Hydrogen peroxide (H2O2) decomposes to form
  water and oxygen gas. If 25.0 grams of hydrogen
  peroxide decompose, how many grams of oxygen will
  be produced?

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• 2. 55.0 grams of hydrogen fluoride are completely
  reacted with tin. How many moles of tin (II)
  fluoride are produced?

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• C. Limiting Excess Reactants
• Reactants are not always completely used up in a
  reaction.
• Excess Reactant reactant that has leftovers at
  the end of the reaction.
• Limiting Reactant reactant that is completely
  used up in the reaction
• makes the least product

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• Example
• 2.25 grams of PCl3 are mixed with
• 1.23 grams of H2O in the following reaction
• PCl3 3H2O ? H3PO3 3HCl
• Calculate the limiting excess reactants

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• b. How many grams of HCl will be produced?
• c. How many grams of the excess reactant
• will be left?

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• D. Percent Yield
• Grams of Product calculated from limiting
  reactant Theoretical Yield
• This is amount of product that should be
  produced if experiment is 100 perfect.
• Amount really produced Actual Yield
• Yield Actual Yield x 100
• Theoretical Yield

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• Example
• When 14.0 grams of nitrogen gas are mixed
• with 9.0 grams of hydrogen gas,
• 16.1 grams of ammonia gas are formed.
• 1. Write a balanced equation for this reaction.

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• 2. Calculate to find the limiting excess
• reactants.
• 3. What is the theoretical yield in grams of
• ammonia?

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• 4. What is the percent yield of ammonia in this
  reaction?
• 5. How many grams of the excess reactant
• are left?