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• Unit 4 Stoichiometry
• Chapter 11 The Mathematics of Chemical Equations

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What is Stoichiometry?

• Stoichiometry is the study of the quantitative,
  or measurable, relationships that exist in
  chemical formulas and chemical reactions.
• The word stoichiometry is derived from two Greek
  words stoicheion (meaning element) and metron
  (meaning measure).

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Why do we use stoichiometry?

• Whenever chemists want to know how much of a
  desired product will be produced, they start with
  a balanced equation.
• Ex. N2H4 2 H2O ? N2 4 H2O

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How does stoichiometry work?

• Chemists use the balanced equation to guide them
  in calculating the products.
• Since stoichiometry is used to predict things in
  the perfect world, we can expect that the
  reaction in real life wont create the maximum
  amount of product.

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Chemical Equation Chemists recipe

• By using the chemical equation, chemists can
  calculate the amount of materials needed or the
  approximate amount of materials produced
• Remember the amount of materials actually
  produced in the lab is approximate since we do
  not live in a perfect world.

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How do I use the chemical equation?

• The chemical equation is written like a
  mathematical expression. When balanced, the
  coefficients tell how many moles of each reactant
  or product is needed or expected.
• Ex. N2H4 2 H2O2 ? N2 4 H2O

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From Math ? English

• One way to understand the information conveyed by
  a chemical equation is to convert the equation
  into an English sentence.
• 1 mole of hydrazine plus 2 moles of hydrogen
  peroxide produces 1 mole of nitrogen and 4 moles
  of water.
• The coefficients tell how many moles, atoms, or
  molecules or each chemical are needed in the
  recipe.

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Quantitative Information from Balanced Equations

• The balanced chemical equation is an algebraic
  equality.
• We can manipulate a balanced equation in much the
  same way as we can manipulate any other algebraic
  equality.

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Stoichiometry has 5 basic steps!

• Step 1 Write and balance the equation.
• Step 2 Write in all information given and
• make sure to identify what you are
• trying to find.
• Step 3 Convert everything to moles.

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Steps Continued

• Step 4 Use mole ratio to solve for what you
• are trying to find.
• Step 5 Convert everything into the required
• unit if needed.

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What is a mole ratio?

• The mole ratio is based on the balanced chemical
  equation.
• Ex. N2H4 2 H2O ? N2 4 H2O
• The mole ratio of N2H4 to H2O is 12
• Another way to write this is N2H4
• H2O

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How do you use a mole ratio?

• The mole ratio is an equivalent which means that
  you can arrange the ratio in any way needed.
• ex. N2 3H2 ? 2NH3
• Write the molar ratios for N2 and H2.
• Write the molar ratios for NH3 and H2
• Convert the ratios above into a fraction.

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Mole Mole Stoichiometry Problem

• 2 H2 O2 ? 2 H2O
• How many moles of H2O are produced when 5 moles
  of oxygen are used?

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Mole Mole Stoichiometry Problem Continued

• 2 H2 O2 ? 2 H2O
• If 3.00 moles of H2O are produced, how many moles
  of oxygen must be consumed?

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Mole Mole Stoichiometry Problem Continued

• 2 H2 O2 ? 2 H2O
• How many moles of hydrogen gas must be used,
  given the data in the previous problem?