Chp 9: Stoichiometry Chocolate Chip Cookies!! 1 cup butter 1/2 cup white sugar 1 cup packed brown...

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Chp 9: Stoichiometry Chp 9: Stoichiometry

Transcript of Chp 9: Stoichiometry Chocolate Chip Cookies!! 1 cup butter 1/2 cup white sugar 1 cup packed brown...

Page 1: Chp 9: Stoichiometry 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.

Chp 9: StoichiometryChp 9: Stoichiometry

Page 2: Chp 9: Stoichiometry 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.

Chocolate Chip Cookies!!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?

Page 3: Chp 9: Stoichiometry 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.

Cookies and Chemistry…Huh!?!?Cookies and Chemistry…Huh!?!?

Just like chocolate chip Just like chocolate chip cookies have recipes, cookies have recipes, chemists have recipes as wellchemists have recipes as well

Instead of calling them Instead of calling them recipes, we call them reaction recipes, we call them reaction equationsequations

Furthermore, instead of using Furthermore, instead of using cups and teaspoons, we use cups and teaspoons, we use molesmoles

Lastly, instead of eggs, butter, Lastly, instead of eggs, butter, sugar, etc. we use chemical sugar, etc. we use chemical compounds as ingredientscompounds as ingredients

Page 4: Chp 9: Stoichiometry 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.

Chemistry RecipesChemistry Recipes

Looking at a reaction tells us how much of Looking at a reaction tells us how much of something you need to react with something you need to react with something else to get a product (like the something else to get a product (like the cookie recipe)cookie recipe)

Be sure you have a balanced reaction Be sure you have a balanced reaction before you start!before you start!

Example: 2 Na + ClExample: 2 Na + Cl2 2 2 NaCl 2 NaClThis reaction tells us that by mixing 2 moles of This reaction tells us that by mixing 2 moles of

sodium with 1 mole of chlorine we will get 2 moles sodium with 1 mole of chlorine we will get 2 moles of sodium chlorideof sodium chloride

What if we wanted 4 moles of NaCl? 10 moles? What if we wanted 4 moles of NaCl? 10 moles? 50 moles?50 moles?

Page 5: Chp 9: Stoichiometry 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.

PracticePractice

Write the balanced reaction for hydrogen gas Write the balanced reaction for hydrogen gas reacting with oxygen gas.reacting with oxygen gas.

2 H2 H22 + O + O22 2 H 2 H22OO How many moles of reactants are needed?How many moles of reactants are needed? What if we wanted 4 moles of water?What if we wanted 4 moles of water? What if we had 3 moles of oxygen, how much hydrogen What if we had 3 moles of oxygen, how much hydrogen

would we need to react, and how much water would we would we need to react, and how much water would we get?get?

What if we had 50 moles of hydrogen, how much oxygen What if we had 50 moles of hydrogen, how much oxygen would we need, and how much water produced? 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

Page 6: Chp 9: Stoichiometry 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.

Mole RatiosMole Ratios

These mole ratios can be used to calculate These mole ratios can be used to calculate the moles of one chemical from the given the moles of one chemical from the given amount of a different chemical amount of a different chemical

Example: How many moles of chlorine are Example: How many moles of chlorine are needed to react with 5 moles of sodium needed to react with 5 moles of sodium (without any sodium left over)?(without any sodium left over)?

2 Na + Cl2 Na + Cl22 2 NaCl 2 NaCl

5 moles Na 1 mol Cl2

2 mol Na= 2.5 moles Cl2

Page 7: Chp 9: Stoichiometry 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.

Mole-Mole ConversionsMole-Mole ConversionsHow many moles of sodium chloride will How many moles of sodium chloride will

be produced if you react 2.6 moles of be produced if you react 2.6 moles of chlorine gas with an excess (more than chlorine gas with an excess (more than you need) of sodium metal?you need) of sodium metal?

2 Na + Cl2 Na + Cl22 2 NaCl 2 NaCl

2.6 moles Cl2 2 mol NaCl

1 mol Cl2= 5.2 moles NaCl

Page 8: Chp 9: Stoichiometry 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.

Mole-Mass ConversionsMole-Mass Conversions

Most of the time in chemistry, the amounts are Most of the time in chemistry, the amounts are given in grams instead of molesgiven in grams instead of moles

We still go through moles and use the mole ratio, We still go through moles and use the mole ratio, but now we also use molar mass to get to gramsbut now we also use molar mass to get to grams

Example: How many grams of chlorine are required Example: How many grams of chlorine are required to react completely with 5.00 moles of sodium to to react completely with 5.00 moles of sodium to produce sodium chloride?produce sodium chloride?

2 Na + Cl2 Na + Cl22 2 NaCl 2 NaCl

5.00 moles Na 1 mol Cl2 70.90g Cl2

2 mol Na 1 mol Cl2

= 177g Cl2

Page 9: Chp 9: Stoichiometry 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.

PracticePractice

Calculate the mass in grams of Iodine Calculate the mass in grams of Iodine required to react completely with 0.50 required to react completely with 0.50 moles of aluminum.moles of aluminum.

2 Al + 3 I2 Al + 3 I2 2 2 AlI 2 AlI3 3

0.50 moles Al 3 moles I2 253.8g I2

2 moles Al 1 mole I2

= 190 g I2

Page 10: Chp 9: Stoichiometry 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.

Mass-MoleMass-MoleWe can also start with mass and convert to We can also start with mass and convert to

moles of product or another reactantmoles of product or another reactantWe use molar mass and the mole ratio to get We use molar mass and the mole ratio to get

to moles of the compound of interestto moles of the compound of interestCalculate the number of moles of ethane (CCalculate the number of moles of ethane (C22HH66) )

needed to produce 10.0 g of waterneeded to produce 10.0 g of water 2 C2 C22HH66 + 7 O + 7 O22 4 CO 4 CO22 + 6 H + 6 H220 0

10.0 g H2O 1 mol H2O 2 mol C2H6

18.0 g H2O 6 mol H20

= 0.185 mol C2H6

Page 11: Chp 9: Stoichiometry 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.

PracticePracticeCalculate how many moles of oxygen are Calculate how many moles of oxygen are

required to make 10.0 g of aluminum oxiderequired to make 10.0 g of aluminum oxide4 Al + 3 O4 Al + 3 O2 2 2 Al 2 Al22OO3 3

10.0g Al10.0g Al22OO3 3 1 mol Al 1 mol Al22OO3 3 3 mol O3 mol O2 2

101.96g Al101.96g Al22OO3 3 2 mol Al 2 mol Al22OO33

= 0.147 mol O= 0.147 mol O22

Page 12: Chp 9: Stoichiometry 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.

Mass-Mass ConversionsMass-Mass Conversions

Most often we are given a starting mass Most often we are given a starting mass and want to find out the mass of a product and want to find out the mass of a product we will get (called theoretical yield) or how we will get (called theoretical yield) or how much of another reactant we need to much of another reactant we need to completely react with it (no leftover completely react with it (no leftover ingredients!)ingredients!)

Now we must go from grams to moles, Now we must go from grams to moles, mole ratio, and back to grams of mole ratio, and back to grams of compound we are interested incompound we are interested in

Page 13: Chp 9: Stoichiometry 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.

Mass-Mass ConversionMass-Mass Conversion

Ex. Calculate how many grams of Ex. Calculate how many grams of ammonia are produced when you react ammonia are produced when you react 2.00g of nitrogen with excess hydrogen.2.00g of nitrogen with excess hydrogen.

NN2 2 + 3 H+ 3 H2 2 2 NH 2 NH33

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

Page 14: Chp 9: Stoichiometry 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.

PracticePractice

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

3 Ca + N3 Ca + N22 Ca Ca33NN22

2.00g Ca 1 mol Ca 1 mol CaCa33NN2 2 148.26g Ca 148.26g Ca33NN2 2

40.08g Ca 3 mol Ca 1 mol 40.08g Ca 3 mol Ca 1 mol CaCa33NN22

= 2.47 g CaCa33NN22

Page 15: Chp 9: Stoichiometry 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.

Limiting Reactant: CookiesLimiting Reactant: Cookies1 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

If we had the specified amount of all ingredients listed, could we make 4 dozen cookies?

What if we had 6 eggs and twice as much of everything else, could we make 9 dozen cookies?

What if we only had one egg, could we make 3 dozen cookies?

Page 16: Chp 9: Stoichiometry 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.

Limiting ReactantLimiting Reactant

Most of the time in chemistry we have more of Most of the time in chemistry we have more of one reactant than we need to completely use one reactant than we need to completely use up other reactant.up other reactant.

That reactant is said to be in That reactant is said to be in excessexcess (there is (there is too much).too much).

The other reactant limits how much product we The other reactant limits how much product we get. Once it runs out, the reaction s. get. Once it runs out, the reaction s. This is called the This is called the limiting reactantlimiting reactant..

Page 17: Chp 9: Stoichiometry 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.

Limiting ReactantLimiting Reactant To find the correct answer, we have to try To find the correct answer, we have to try allall of of

the reactants. We have to calculate how much the reactants. We have to calculate how much of of aa product we can get from product we can get from eacheach of the of the reactants to determine which reactant is the reactants to determine which reactant is the limiting one.limiting one.

The The lowerlower amount of amount of aa product is the correct product is the correct answer.answer.

The reactant that makes the least amount of The reactant that makes the least amount of product is the product is the limiting reactantlimiting reactant. Once you . Once you determine the limiting reactant, you should determine the limiting reactant, you should ALWAYS start with it!ALWAYS start with it!

Be sure to pick Be sure to pick aa product! You can’t compare to product! You can’t compare to see which is greater and which is lower unless see which is greater and which is lower unless the product is the same!the product is the same!

Page 18: Chp 9: Stoichiometry 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.

Limiting Reactant: ExampleLimiting Reactant: Example 10.0g of aluminum reacts with 35.0 grams of 10.0g of aluminum reacts with 35.0 grams of

chlorine gas to produce aluminum chloride. Which chlorine gas to produce aluminum chloride. Which reactant is limiting, which is in excess, and how reactant is limiting, which is in excess, and how much product is produced?much product is produced?

2 Al + 3 Cl2 Al + 3 Cl22 2 AlCl 2 AlCl33 Start with Al:Start with Al:

Now ClNow Cl22::

10.0 g Al 1 mol Al 2 mol AlCl3 133.5 g AlCl3

27.0 g Al 2 mol Al 1 mol AlCl3

= 49.4g AlCl3

35.0g Cl2 1 mol Cl2 2 mol AlCl3 133.5 g AlCl3

71.0 g Cl2 3 mol Cl2 1 mol AlCl3

= 43.9g AlCl3

LimitingLimitingReactantReactant

Page 19: Chp 9: Stoichiometry 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.

LR Example ContinuedLR Example Continued

We get We get 49.4g49.4g of aluminum chloride from the of aluminum chloride from the given amount of aluminum, but only given amount of aluminum, but only 43.9g43.9g of of aluminum chloride from the given amount of aluminum chloride from the given amount of chlorine. Therefore, chlorine is the limiting chlorine. Therefore, chlorine is the limiting reactant. Once the 35.0g of chlorine is used reactant. Once the 35.0g of chlorine is used up, the reaction comes to a up, the reaction comes to a complete .complete .

Page 20: Chp 9: Stoichiometry 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.

Limiting Reactant PracticeLimiting Reactant Practice

15.0 g of potassium reacts with 15.0 g 15.0 g of potassium reacts with 15.0 g of iodine. Calculate which reactant is of iodine. Calculate which reactant is limiting and how much product is limiting and how much product is made.made.

Page 21: Chp 9: Stoichiometry 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.

Limiting Reactant PracticeLimiting Reactant Practice

2 K + I2 K + I22 2 KI 2 KIPotassium:Potassium:

Iodine:Iodine:

Iodine is the limiting reactant and we get Iodine is the limiting reactant and we get 19.6 g of potassium iodide19.6 g of potassium iodide

15.0g K 1 mol K 2 mol KI 166 g KI

39.1g K 2 mol K 1 mol KI= 63.7g KI

15.0 g I2 1 mol I2 2 mol KI 166 g KI

254 g I2 1 mol I2 1 mol KI= 19.6 g KI

Page 22: Chp 9: Stoichiometry 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.

Finding the Amount of ExcessFinding the Amount of Excess

By calculating the amount of the excess By calculating the amount of the excess reactant needed to completely react reactant needed to completely react with the limiting reactant, we can with the limiting reactant, we can subtract that amount from the given subtract that amount from the given amount to find the amount of excess.amount to find the amount of excess.

Can we find the amount of excess Can we find the amount of excess potassium in the previous problem?potassium in the previous problem?

Page 23: Chp 9: Stoichiometry 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.

Finding Excess PracticeFinding Excess Practice 15.0 g of potassium reacts with 15.0 g of iodine. 15.0 g of potassium reacts with 15.0 g of iodine.

2 K + I2 K + I22 2 KI 2 KI We found that Iodine is the limiting reactant, We found that Iodine is the limiting reactant,

and 19.6 g of potassium iodide are produced.and 19.6 g of potassium iodide are produced.15.0 g I2 1 mol I2 2 mol K 39.1 g K

254 g I2 1 mol I2 1 mol K= 4.62 g K USED!

15.0 g K – 4.62 g K = 10.38 g K EXCESS

Given amount of excess reactant

Amount of excess reactant actually used

Note that we started with the limiting reactant! Once you determine the LR, you should only start with it!

Page 24: Chp 9: Stoichiometry 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.

Limiting Reactant: RecapLimiting Reactant: Recap

1.1. You can recognize a limiting reactant problem You can recognize a limiting reactant problem because there is MORE THAN ONE GIVEN because there is MORE THAN ONE GIVEN AMOUNT.AMOUNT.

2.2. Convert ALL of the reactants to the SAME product Convert ALL of the reactants to the SAME product (pick any product you choose.)(pick any product you choose.)

3.3. The lowest answer is the correct answer.The lowest answer is the correct answer.4.4. The reactant that gave you the lowest answer is The reactant that gave you the lowest answer is

the LIMITING REACTANT.the LIMITING REACTANT.5.5. The other reactant(s) are in EXCESS.The other reactant(s) are in EXCESS.6.6. To find the amount of excess, subtract the amount To find the amount of excess, subtract the amount

used from the given amount.used from the given amount.7.7. If you have to find more than one product, be sure If you have to find more than one product, be sure

to start with the limiting reactant. You don’t have to start with the limiting reactant. You don’t have to determine which is the LR over and over again!to determine which is the LR over and over again!