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“Sounds cool….”

Consider: 4NH3 + 5O2 6H2O + 4NO

Stoichiometry- What do the coefficients tell us?
- 4 molecules of ammonia react with 5 molecules of oxygen to produce 6 molecules of water and 4 molecules of nitrogen monoxide
- 4 moles of NH3 react with 5 moles of O2 to produce 6 moles of H2O and 4 moles of NO
- The “ratio” of NH3 to O2 is 4:5

Proportional Relationships

2 1/4 c. flour

1 tsp. baking soda

1 tsp. salt

1 c. butter

3/4 c. sugar

3/4 c. brown sugar

1 tsp vanilla extract

2 eggs

2 c. chocolate chips

Makes 5 dozen cookies.

I have 5 eggs. How many cookies can I make?

2 eggs

5 doz.

5 eggs

X doz.

=

X = 12.5 dozen cookies

150 cookies

Courtesy Christy Johannesson www.nisd.net/communicationsarts/pages/chem

Proportional Relationships

- Stoichiometry
- mass relationships between substances in a chemical reaction
- based on the mole ratio
- Mole Ratio
- indicated by coefficients in a balanced equation

2 Mg + O2 2 MgO

Courtesy Christy Johannesson www.nisd.net/communicationsarts/pages/chem

Known Unknown

Substance A Substance B

M

Mass

Mass Mountain

Mass

Mole Island

Volume

Mole

Mole

Volume

V

Liter Lagoon

Particles

Particles

P

Particle Place

Stoichiometry Island Diagram

Stoichiometry Steps

1. Write a balanced equation.

2. Identify known & unknown.

3. Convert the known substance to moles.

- Using the mole ratios of the known and unknown substance, obtain the # of moles for the unknown.

5. Convert the # of moles of the unknown into value requested (mass. Volume…etc.)

- Mole ratio - moles moles

Core step in all stoichiometry problems!!

6. Check answer.

Courtesy Christy Johannesson www.nisd.net/communicationsarts/pages/chem

Example 1: How many moles of KClO3 must decompose in order to produce 9 moles of oxygen gas?

? mol

9 mol

x mol KClO3

9 mol O2

2 mol KClO3

3 mol O2

= 6 mol KClO3

=

Courtesy Christy Johannesson www.nisd.net/communicationsarts/pages/chem

6 mol H2O

x mol H2O

4 mol NO

0.2112 mol H2O

x =

=

11.33 mol NO

x=

17 mol H2O

0.176 mol O2

5 mol O2

6 mol H2O

Example 2:Consider : 4NH3 + 5O2 6H2O + 4NO

- How many moles of H2O are produced if 0.176 mol of O2 are used?
- How many moles of NO are produced in the reaction if 17 mol of H2O are also produced?

=

Notice that a correctly balanced equation is essential to get the right answer

Example 3: How many grams of silver will be formed from 12.0 g copper?

12.0 g

? g

n Cu =

12.0 g

= 0.189 mol Cu

63.55 g/mol

2 mol Ag

1 mol Cu

x mol Ag

0.189 mol Cu

x = 0.378 mol Ag

=

m Ag =

0.378 mol x 107.97 g/mol

= 40.8 g Ag

Courtesy Christy Johannesson www.nisd.net/communicationsarts/pages/chem

Example 4

2 TiO2 + 4 Cl2 + 3 C

CO2 + 2 CO + 2 TiCl4

x molecules

115 g

How many molecules of TiCl4 will be produced by 115.0g TiO2?

3. Convert # of moles of TiCl4

to number of molecules

- Convert mass to moles

115.0 g

79.88 g/mol

n TiO2 =

= 1.440 mol

N = n NA

= (1.440 mol) (6.022 x 1023molecules/mol)

2. Use mole ratio to obtain # of moles of TiCl4

= 8.672 x 1023 molecules of TiCl4

Therefore, 8.672 x 1023 molecules of TiCl4 will be produced from 115.0 g of TiO2.

2 mol TiO2

2 mol TiCl4

1.440 mol TiO2

x mol TiCl4

=

x = 1.440 mol TiCl4

Homework

- Read 7.1
- Pg 320 # 1-7
- Read 7.2
- Pg 325 # 1, 2, 5-10

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