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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?

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.

Terms chapter seven

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

Skills chapter 7.1

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

- 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.

- 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

- 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.

Burning of Carbon

Figure 2

Burning of Carbon

Burning of Carbon

Burning of Carbon

Atom inventory C 1 C 1 O 2 O

2

The formation of water

The formation of water

Atom inventory Reactants Products H 4 H

4 O 2 O 2

Combustion of Propane

Figue 17

Combustion of Propane

Figure 17

Combustion of Propane

Figure 17

Combustion of Propane

Figure 17

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

- 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

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

- 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

- 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

Answers to Cons. of atoms ex.

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

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

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

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

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

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

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

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

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.

CH4 O2 ? H2O CO2

Atom Inventory Reactants Products C 1 C

1 H 4 H 2 O 2 O 3 Equation is not

balanced!

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.

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!

- 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.

CH4 2O2 ? 2H2O CO2

Atom Inventory Reactants Products C 1 C

1 H 4 H 4 O 4 O 4 Equation is

balanced!

- Only coefficients may be added or changed.
- You may not change any subscripts or formulas in

order to balance the equation.

N2 H2 ? NH3 Atom

Inventory Reaactants Products N 2 N 1 H

2 H 3 Equation is not balanced!

N2 H2 ? 2NH3 Atom

Inventory Reaactants Products N 2 N 2 H

2 H 6 Equation is not balanced!

N2 3H2 ? 2NH3 Atom

Inventory Reaactants Products N 2 N 2 H

6 H 6 Equation is balanced!

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.