introduction to stocihiometry milestone
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Chemistry stoich powerpointTRANSCRIPT
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Stoichiometry
Chemistry
Chapter 9 Pg 237-261
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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.
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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
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Review Prior Learning
The Mole Avogadro’s number Molar Mass Mole map
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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)
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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 = 12.0 g
1 mole of Mg atoms = 24.3 g
1 mole of O2 molecules = 32.0 g
Molar Mass
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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
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FlowchartAtoms or Molecules
Moles
Mass (grams)
Divide by 6.02 X 1023
Multiply by 6.02 X 1023
Multiply by atomic/molar mass from periodic table
Divide by atomic/molar mass from periodic table
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Practice
Calculate the Molar Mass of calcium phosphate Formula = Masses elements:
Ca: 3 Ca’s X 40.1 = P: 2 P’s X 31.0 = O: 8 O’s X 16.0 =
Molar Mass =
Ca3(PO4)2
120.3 g
62.0 g
128.0 g
120.3g + 62.0g +128.0g310.3 g/mol
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molar mass Avogadro’s number Grams Moles particles
Everything must go through Moles!!!
Calculations
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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
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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
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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
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Applying Stoichiometry to chemical equations
Chapter 9 Pg 237
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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.
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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?
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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
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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
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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.
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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
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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.
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Product
Summarize the relationship between the reactants and products using a real life, nonchemical process such as making a circuit work.
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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.
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Interesting Facts
Ratio of
Ratio of
Ratio of
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What is a RATIO?
In math…………. What does it tell you? How can it be written?
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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.
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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?
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Practice
Write the balanced reaction for hydrogen gas reacting with oxygen gas.
2 H2 + O2 2 H2O How many moles of reactants are needed? What if we wanted 4 moles of water?
What if we had 3 moles of oxygen, how much hydrogen would we need to react and how much water would we get?
What if we had 50 moles of hydrogen, how much oxygen would we need and how much water produced?
2 mol H2 1 mol O2
4 mol H2
2 mol O2
6 mol H2, 6 mol H2O
25 mol O2, 50 mol H2O
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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
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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
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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 70.90g Cl2
2 mol Na 1 mol Cl2
= 177g Cl2
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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
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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
18.0 g H2O 6 mol H20
= 0.185 mol C2H6
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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
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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 1 mol NH3
= 2.4 g NH3
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Practice
How many grams of calcium nitride are produced when 2.00 g of calcium reacts with an excess of nitrogen?