Chemistry stoich powerpoint

1. Stoichiometry
Chemistry
Chapter 9 Pg 237-261

2. Learning Goals Dy1
 Objective:
 We will calculate the amount of reactants
required or products formed in a nonchemical
process.
 Product:
 I will describe the relationship between the
reactants and products using a real life,
nonchemical process.

3. Agenda
 Bell Ringer
 Review prior learning
 New learning
What is Stoichiometry?
 How does it relate to a recipe?
 How can we use a balanced chemical
reaction?

 Product

4. Review Prior Learning
 The Mole
 Avogadro’s number
 Molar Mass
 Mole map

5. The Mole
 A counting unit
 Similar to a dozen, except instead of 12,
it’s 602,000,000,000,000,000,000,000
 6.02 X 1023 (in scientific notation)
 This number is named in honor of
Amedeo Avogadro (1776 – 1856)

6. Molar Mass
 The Mass of 1 mole (in grams)
 Equal to the numerical value of the average atomic
mass (get from periodic table), or add the atoms
together for a molecule
1 mole of C atoms
=
1 mole of Mg atoms
1 mole of O2 molecules
12.0 g
=
=
32.0 g
24.3 g

7. Molar Mass of Compounds
 The molar mass (MM) of a compound is determined
the same way, except now you add up all the atomic
masses for the molecule (or compound)
Ex. Molar mass of CaCl2
 Avg. Atomic mass of Calcium = 40.08g
 Avg. Atomic mass of Chlorine = 35.45g
 Molar Mass of calcium chloride =
40.08 g/mol Ca + (2 X 35.45) g/mol Cl
 110.98 g/mol CaCl2

20
Ca
40.08
17
Cl
35.45

8. Atoms or
Molecules
Flowchart
Divide by 6.02 X 1023
Multiply by 6.02 X 1023
Moles
Multiply by atomic/molar mass
from periodic table
Divide by atomic/molar
mass from periodic table
Mass
(grams)

9. Practice
 Calculate the Molar Mass of calcium
phosphate


Formula =
Ca3(PO4)2
Masses elements:
 Ca: 3 Ca’s X 40.1 =
 P: 2 P’s X 31.0 =
 O: 8 O’s X 16.0 =
120.3 g
62.0 g
128.0 g

Molar Mass =
120.3g + 62.0g +128.0g
310.3 g/mol

10. Calculations
molar mass
Grams
Avogadro’s number
Moles
particles
Everything must go through
Moles!!!

11. Atoms/Molecules and Grams
How many moles of Cu are present in 35.4 g of Cu?
How many atoms?
35.4 g x 1 mol = 0.557 mol Cu
63.55 g
0.557 mol Cu x 6.02x1023 atoms = 3.35x1023 atoms
1 mol

12. On your own!
How many moles of Fe are present in 102.4 g of
Fe? How many atoms?
102.4 g x 1 mol = 1.83 mol Fe
55.85 g
1.83 mol Fe x 6.02x1023 atoms = 1.10x1024 atoms
1 mol

13. Work backwards!
What is the mass (in grams) of 1.20x1024 molecules
of glucose (C6H12O6)?
1.20x1024 molec. X 1 mol = 1.99 mol
6.02x1023 molec.
1.99 mol x 180.12 g = 358.4 g
1 mol
From periodic table

14. Applying Stoichiometry
to chemical equations
Chapter 9 Pg 237

15. What is Stoichiometry?
 Calculations of quantities in balanced
chemical reactions.
 Balanced Equations are recipes that tell
chemists what amounts of reactants to mix
and what amount of products to expect.
 Let’s look at some recipes.

16. Chocolate Chip Cookies!!
1 cup butter
1/2 cup white sugar
1 cup packed brown sugar
1 teaspoon vanilla extract
2 eggs
2 1/2 cups all-purpose flour
1 teaspoon baking soda
1 teaspoon salt
2 cups semisweet chocolate chips
Makes 3 dozen
How many eggs are needed to make 3 dozen cookies?
How much butter is needed for the amount of chocolate chips
used?
How many eggs would we need to make 9 dozen cookies?
How much brown sugar would I need if I had 1 ½ cups white sugar?

17. Cookies and Chemistry
 Just like chocolate chip cookies
have recipes, chemists have recipes
as well
 Instead of calling them recipes, we
call them reaction equations
 Furthermore, instead of using cups
and teaspoons, we use moles
 Lastly, instead of eggs, butter,
sugar, etc. we use chemical
compounds as ingredients

18. Guided Practice
 In a 5 day workweek, Tiny Tyke is scheduled
to make 640 tricycles. How many wheels
should be in the plant on Monday morning to
make these tricycles?
 Use the equation recipe on page 238.
 F+S+3W+H+2P FSW3HP2
 F- frame S-seat W-wheels H-handlebars P-
pedals

19. Guided Example
 Your group has been selected to prepare a
cake for the class bake sale. You can calculate
the number of cakes that you can make from
the ingredients you have by using the recipe.

20.  Write the “Cake Equation”
 4cupsflour + 1 stick butter + 4 eggs + 4cups
sugar + 3 cups milk + 1 spoon baking powder
= 1 cake
 You have these ingredients:
 5 cups of flour,6 cups of sugar,6 eggs, 6
cups of milk, a lot of baking powder, 3 sticks
of butter

21. Closure
 Stoichiometry will include conversions
between different substances and amounts
indicating how much are necessary for a
given reaction.
 A chemical equation is similar to a recipe.
 The amount of product made depends on the
amount of reactants available.

22. Product
 Summarize the relationship between the
reactants and products using a real life,
nonchemical process such as making a
circuit work.

23. Mole to Mole conversions ( dy2)
 We will construct mole ratios and use them
to solve problems
 I will describe the relationship between the
reactants and products using mole ratios.

24. Interesting Facts
 Ratio of
 Ratio of
 Ratio of

25. What is a RATIO?
 In math………….
 What does it tell you?
 How can it be written?

26. What information can we get?
 From a balanced equation:
 N2 + 3H2  2NH3
 Moles?
 Note: Coefficient in a balanced equation tells
us the number of moles.

27. Chemistry Recipes
 Looking at a reaction tells us how much of
something you need to react with something
else to get a product (like the cookie recipe)
 Be sure you have a balanced reaction before
you start!



Example: 2 Na + Cl2  2 NaCl
This reaction tells us that by mixing 2 moles of
sodium with 1 mole of chlorine we will get 2 moles of
sodium chloride
What if we wanted 4 moles of NaCl? 10 moles?
50 moles?

28. Practice
 Write the balanced reaction for hydrogen gas reacting with
oxygen gas.
2 H2 + O2  2 H2O
2 mol H2
How many moles of reactants are needed?
1 mol O2
 What if we wanted 4 moles of water?
4 mol H2
2 mol O2


What if we had 3 moles of oxygen, how much hydrogen would
we need to react and how much water would we get?
6 mol H2, 6 mol H2O

What if we had 50 moles of hydrogen, how much oxygen
would we need and how much water produced?
25 mol O2, 50 mol H2O

29. Mole Ratios
 These mole ratios can be used to calculate the
moles of one chemical from the given amount of a
different chemical
 Example: How many moles of chlorine is needed to
react with 5 moles of sodium (without any sodium left
over)?
2 Na + Cl2  2 NaCl
5 moles Na 1 mol Cl2
2 mol Na
= 2.5 moles Cl2

30. Mole-Mole Conversions
 How many moles of sodium chloride will be
produced if you react 2.6 moles of chlorine gas
with an excess (more than you need) of sodium
metal?
2 Na + Cl2  2 NaCl
2.6 moles Cl2 2 mol NaCl
1 mol Cl2
= 5.2 moles NaCl

31. Mole-Mass Conversions
 Most of the time in chemistry, the amounts are given in
grams instead of moles
 We still go through moles and use the mole ratio, but now
we also use molar mass to get to grams
 Example: How many grams of chlorine are
required to react completely with 5.00 moles of
sodium to produce sodium chloride?
2 Na + Cl2  2 NaCl
5.00 moles Na 1 mol Cl2
2 mol Na
70.90g Cl2
1 mol Cl
= 177g Cl2

32. You Practice
 Calculate the mass in grams of Iodine
required to react completely with 0.50 moles
of aluminum.
2 Al + 3 I2  2 AlI3

33. Mass-Mole
 We can also start with mass and convert to moles of
product or another reactant
 We use molar mass and the mole ratio to get to
moles of the compound of interest
Calculate the number of moles of ethane (C2H6)
needed to produce 10.0 g of water
 2 C2H6 + 7 O2  4 CO2 + 6 H20

10.0 g H2O 1 mol H2O
2 mol C2H6 = 0.185
18.0 g H2O 6 mol H20
mol C2H6

34. Mass-Mass Conversions
 Most often we are given a starting mass and
want to find out the mass of a product we will get
(called theoretical yield) or how much of another
reactant we need to completely react with it (no
leftover ingredients!)
 Now we must go from grams to moles, mole
ratio, and back to grams of compound we are
interested in

35. Mass-Mass Conversion
 Ex. Calculate how many grams of ammonia
are produced when you react 2.00g of
nitrogen with excess hydrogen.
 N2 + 3 H2  2 NH3
2.00g N2
1 mol N2
2 mol NH3 17.06g NH3
28.02g N2 1 mol N2
= 2.4 g NH3
1 mol NH3

36. Practice
 How many grams of calcium nitride are
produced when 2.00 g of calcium reacts with
an excess of nitrogen?