Equation Analogy

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Section 7.1

• Equation Analogy
• Imagine that you work at a skateboard shop and
  you are in charge of assembling the skateboards.
  Every skateboard requires one deck (the board),
  two trucks (the mounted axles), and four wheels.
• 1. Your boss asks you to make five skateboards.
  How many trucks do you need?
• 2. The following diagram shows the recipe for
  one skateboard. What do you notice about the
  relative amounts of each part on either side of
  the arrow?

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Answers
Section 7.1

• 1. Your boss asks you to make five skateboards.
  How many trucks do you need?
• 10
• 2. The following diagram shows the recipe for
  one skateboard. What do you notice about the
  relative amounts of each part on either side of
  the arrow?
• There are the same numbers of each part on
  either side of the arrow.

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Terms chapter seven

• Symbol
• Subscript
• Formula
• Equation
• Coefficient
• Atom inventory
• Balanced
• Conservation of atoms

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Skills chapter 7.1

• How do you do an atom inventory?
• How do you balance an equation?

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• Symbol shorthand for an atom of an element.
• Formula shorthand for the molecules or basic
  units of a compound.
• Equation shorthand for what happens during a
  chemical change.

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• Subscripts in a chemical formula tell how many
  atoms of an element are present in that
  compounds basic unit
• Coefficients in a balanced equation tell how many
  units of each reactant are needed and how many
  units of each product are made.
• Coefficients tell the reacting ratio
• 2Na Cl2 ? 2 NaCl

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• Reactants starting materials
• Products end resulting materials
• Law of conservation of atoms The atoms present
  in the reactants are rearranged to form the
  products. Atoms are not lost or gained during a
  reaction.

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Burning of Carbon
Figure 2
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Burning of Carbon
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Burning of Carbon
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Burning of Carbon
Atom inventory C 1 C 1 O 2 O
2
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The formation of water
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The formation of water
Atom inventory Reactants Products H 4 H
4 O 2 O 2
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Combustion of Propane
Figue 17
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Combustion of Propane
Figure 17
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Combustion of Propane
Figure 17
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Combustion of Propane
Figure 17
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Answers to paper clip activity

• SO2 H2O ?H2SO3
• Reactants Products
• S 1 S1
• O3 O3
• H2 H2 balanced
• 2H2S 3O2 ? 2SO2 2H2O
• reactants products
• H4 H4
• S2 S2
• O6 O6 balanced

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• 3. CS2 3O2 ? 2SO2 CO2
• reactants products
• C1 C1
• S2 S2
• O6 O6 balanced
• 4. N2 3H2? 2NH3
• reactants products
• N2 N2
• H6 H6 balanced

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• 5. 2NO O2 ? 2NO2
• reactants products
• N2 N2
• O4 O4 balanced
• 6. 3O2?2O3
• reactants products
• O6 O6 balanced

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• H2SO3 ? H2O SO2
• reactants products
• H 2 H2
• S1 S1
• O3 O3 balanced
• C6H12O6 6O2 ? 6 CO2 6 H2O
• reactants products
• C6 C6
• H12 H12
• O18 O18 balanced

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• 9. N2 O2 ? 2NO
• reactants products
• N2 N2
• O2 O2 balanced
• 10. CH4 2O2 ? CO2 2H2O
• reactants products
• C 1 C 1
• H 4 H 4
• O 4 O 4 balanced

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Answers to Cons. of atoms ex.

• 2a. N2 O2 ? 2NO
• Reactants products
• N2 N2
• O2 O2

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• 2b. 2NO O2 ? 2NO2
• Reactants products
• N2 N2
• O4 O4

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• 2c. H2O 2NO2? HNO3 HNO2
• reactants products
• H2 H2
• N 2 N2
• O 5 O5

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• 2d. N2 3H2 ? 2NH3
• reactants products
• N2 N2
• H 6 H6

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• 2e. 4NH3 5O2 ? 4 NO 6H2O
• reactants products
• N4 N4
• H12 H12
• O10 O10

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• 2f. NH3 HNO3 ? NH4NO3
• reactants products
• N2 N 2
• H 4 H 4
• O 3 O 3

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• 3a. C6H12O6 6O2 ? 6 CO2 6 H2O
• reactants products
• C6 C6
• H12 H12
• O18 O18

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• 3b. 6 CO2 6 H2O ?C6H12O6 6O2
• reactants products
• C6 C6
• H12 H12
• O18 O18

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When to balance an equation

• For the equation as it is given do an atom
  inventory.
• If the atom inventory is the same on both sides,
  the equation is correctly balanced and you are
  finished!
• If the atom inventory is not the same, it is not
  balanced and you need to balance the equation.

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CH4 O2 ? H2O CO2
Atom Inventory Reactants Products C 1 C
1 H 4 H 2 O 2 O 3 Equation is not
balanced!
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How to balance an equation

• A coefficient is changed or added in front of any
  formula to increase the number of atoms of a
  particular element.
• Update your inventory after adding or changing a
  coefficient.

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CH4 O2 ? 2H2O CO2
Atom Inventory Reactants Products C 1 C
1 H 4 H 4 O 2 O 4 Equation is still
not balanced!
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• Keep adding and/or changing the coefficients in
  front of the formulas until both checklists in
  your atom inventory are the same.
• When both lists are the same, the equation is
  balanced and you can stop.

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CH4 2O2 ? 2H2O CO2
Atom Inventory Reactants Products C 1 C
1 H 4 H 4 O 4 O 4 Equation is
balanced!
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• Only coefficients may be added or changed.
• You may not change any subscripts or formulas in
  order to balance the equation.

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N2 H2 ? NH3 Atom
Inventory Reaactants Products N 2 N 1 H
2 H 3 Equation is not balanced!
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N2 H2 ? 2NH3 Atom
Inventory Reaactants Products N 2 N 2 H
2 H 6 Equation is not balanced!
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N2 3H2 ? 2NH3 Atom
Inventory Reaactants Products N 2 N 2 H
6 H 6 Equation is balanced!
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Answers to Balancing Equations

• CH4 2O2 ? CO2 2H2O
• Zn 2HCl ? H2 ZnCl2
• 2C O2 ? 2CO
• H2 S ? H2S
• 4Al 3O2 ?2Al2O3
• 4Li O2 ? 2Li2O
• 3Mg N2 ? Mg3N2
• 4NH3 5O2 ? 6H2O 4NO

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Quiz on monday

• Be able to do an atom inventory
• Be able to balance an equation
• Be able to draw or to interpret models for
  equations.