Tuesday, Sept. 24th:

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Tuesday, Sept. 24th A DayWednesday, Sept.
25th B DayAgenda

• Ch. 8 Tests
• Begin Ch. 9 Stoichiometry
• Start Sec 9.1 Calculating Quantities in
  Reactions
• Stoichiometry, mole ratios
• Moles Moles
• Moles Mass
• In-Class
• Worksheet pg. 14-15 (moles moles)
• Mass to Mass Stoichiometry worksheet
• You MUST show work for credit!

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Ch. 8 TestChemical Equations and Reactions
Class Average Score (out of 60) Average Percentage
3A 53.09 88.48
4B 51.23 85.38
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Balanced Equations Show Proportions

• The proportions of the ingredients in a muffin
  recipe let you adjust the amounts to make enough
  muffins even if you dont have balanced amounts
  initially.
• A balanced chemical equation is very similar to a
  recipe in that the coefficients in the balanced
  equation show the proportions of the reactants
  and products.
• Consider the reaction for the synthesis of water

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Balanced Equations Show Proportions

• 2 H2 O2 2 H2O
• The coefficients show that two molecules of
  hydrogen react with one molecule of oxygen and
  form two molecules of water.
• Calculations that involve chemical reactions use
  the proportions from balanced chemical equations
  to find the quantity of each reactant and product
  involved.

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Relative Amounts in Equations can be Expressed in
Moles

• The coefficients in a balanced equation also
  represent the moles of each substance.
• For example, the equation below shows that
• 2 mol C8H18 react with 25 mol O2 to form
• 16 mol CO2 and 18 mol H2O.
• 2 C8H18 25 O2 ? 16 CO2 18 H2O

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Relative Amounts in Equations can be Expressed in
Moles

• You can determine how much of a reactant is
  needed to produce a given quantity of product, or
  how much of a product is formed from a given
  quantity of reactant.
• The branch of chemistry that deals with
  quantities of substances in chemical reactions is
  known as stoichiometry.
• Stoichiometry the proportional relationship
  between two or more substances during
• a chemical reaction.

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The Mole Ratio is the Key

• The coefficients in a balanced chemical equation
  show the relative numbers of moles of the
  substances in the reaction.
• As a result, you can use the coefficients in
  conversion factors called mole ratios.
• Mole ratios bridge the gap and can convert from
  moles of one substance to
• moles of another.

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The Mole Ratio is the Key!

• The mole ratio is..
• THE SECRET MAGIC STEP!!
• when solving stoichiometry problems.

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All stoichiometry problems can be solved by
following these 3 steps

• Change the units of what you know into moles.
• Use the mole ratio (secret magic step) to convert
  moles of the substance you were given into moles
  of the substance you want.
• Change out of moles into the unit that you need
  for your final answer.
• Thats all there is to it!

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Sample Problem A, pg. 304

• Consider the Haber process for the commercial
  preparation of ammonia, NH3
• N2 3 H2 2 NH3
• Question How many moles of hydrogen, H2, are
  needed to prepare 312 moles of ammonia, NH3?
• Start with what you know 312 moles NH3
• Use the secret magic step to convert moles of
  NH3 into moles of what you want, H2.
• 312 mol NH3 X 3 mol H2
• 2 mol NH3
• 468 mol H2

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Practice 1, pg. 304

• Calculate the amounts requested if 1.34 mol H2O2
  completely react according to the following
  equation 2 H2O2 2 H2O O2
• Moles of oxygen formed
• 1.34 mol H2O2 X 1 mol O2 0.670 mol O2
• 2 mole H2O2
• b. Moles of water formed
• 1.34 mol H2O2 X 2 mol H2O 1.34 mol H2O
• 2 mol H2O2

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Practice 2, pg. 304

• Calculate the amounts requested if 3.30 mol Fe2O3
  completely react according to the following
  equation
• Fe2O3 2 Al 2 Fe Al2O3
• a) Moles of aluminum needed
• 6.60 mol Al
• b) Moles of iron formed
• 6.60 mol Fe
• c) Mole of aluminum oxide formed
• 3.30 mol Al2O3

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Problems Involving Mass, Volume, or Particles

• Substances are usually measured by mass or
  volume. (Can you go to the balance and measure
  out 5 moles of NaCl?)
• As a result, before using the mole ratio
• (Secret Magic Step) you will need to convert
  units for mass and volume into moles.

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Mass Moles

• The conversion factor for converting between mass
  and moles is simply the molar mass of the
  substance.
• You do remember molar mass, dont you?.....

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Molar Mass Review

• What is the molar mass of table salt, NaCl?
• Na 22.99 g/mol
• Cl 35.45 g/mol
• 58.44 g/mol
• What is the molar mass of sulfuric acid, H2SO4?
• H 2 (1.01 g/mol) 2.02 g/mol
• S 32.07 g/mol
• O 4 (16.00 g/mol) 64.00 g/mol
• 98.09 g/mol
• OK, I feel better now that you guys remember this
  stuff. Lets try a sample problem

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Remember the 3 steps

• Change the units of what you know into moles.
• Use the mole ratio (secret magic step) to convert
  moles of the substance you were given into moles
  of the substance you want.
• Change out of moles into the unit that you need
  for your final answer.

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Sample Problem B, pg. 307

• What mass of NH3 can be made from 1,221 g H2 and
  excess N2? N2 3 H2 2 NH3
• Remember, hydrogen is a diatomic element
• Start with what you know 1,221 g H2
• Convert to moles using molar mass
• 1,221 g H2 X 1 mol H2 604.5 mol H2
• 2.02 g H2
• 3. Use mole ratio to convert moles H2
  moles NH3
• 604.5 mol H2 X 2 mol NH3 403.0 mol NH3
• 3 mol H2

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Sample Problem B cont

• Finally, use the molar mass to change moles of
  NH3 into grams of NH3
• 403.0 mol NH3 X 17.04 g NH3 6,867 g NH3
• 1 mol NH3
• Thats ityou did it!

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Practice 1, pg. 307

• Use the equation below to answer the questions
  that follow
• Fe2O3 2Al 2Fe Al2O3
• How many grams of Al are needed to completely
  react with 135 g Fe2O3?
• How many grams of Al2O3 can form when 23.6 g Al
  react with excess Fe2O3?
• How many grams of Fe2O3 react with excess Al to
  make 475 g Fe?
• How many grams of Fe will form when 97.6 g Al2O3
  form?

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Update your graphic organizer

• What do you use to change from
• Moles Moles
• Mole Ratio
• Secret Magic Step
• What do you use to change from
• Moles Mass
• Molar Mass
• (g/mol)

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In-Class/Homework Assignment

• Worksheet pg. 14-15 (moles moles)
• Mass to Mass Stoichiometry worksheet
• We will finish section 9.1 next time.
• You must SHOW ALL WORK on these worksheets for
  credit