StoichiometryStoichiometry

Chapter 11Chapter 11

11.1 Stoichiometry11.1 Stoichiometry

StoichiometryStoichiometry is the study of quantitative is the study of quantitative relationships between the amounts of relationships between the amounts of reactants used and amounts of products reactants used and amounts of products formed by a chemical reaction.formed by a chemical reaction.

– 2 slices of bread + 1 slice of ham 1 ham sandwich

How do you figure out a chemical equation’s recipe?How do you figure out a chemical equation’s recipe?

NN22 + 3H + 3H22 2NH 2NH33

This 1:3:2 ratio can symbolize numbers of molecules or This 1:3:2 ratio can symbolize numbers of molecules or moles.moles.

Mole RelationshipsMole Relationships

Mole RatioMole Ratio: a ratio between the : a ratio between the numbers of moles of any two of the numbers of moles of any two of the substances in a balanced chemical substances in a balanced chemical equation.equation.

What are all of the possible mole ratios in the What are all of the possible mole ratios in the equation?equation?– 4Al(s) + 3O4Al(s) + 3O22(g) (g) → 2Al→ 2Al22OO33(s)(s)

Mole/Mole Mole/Mole StoichiometryStoichiometry

Moles of known x mole ratio = moles of Moles of known x mole ratio = moles of unknownunknown

substancesubstance substancesubstance

– Mole ratio = Mole ratio = moles of unknown (coefficient)moles of unknown (coefficient)

moles of known (coefficient)moles of known (coefficient)

2 slices of bread + 1 slice of ham 1 ham sandwichIf you have 10 slices of bread how many slices of ham are

needed?

Mole/Mole Mole/Mole StoichiometryStoichiometry Find the quantities of reactants Find the quantities of reactants

and products in chemical and products in chemical reactions reactions

Use the mole ratio to convert Use the mole ratio to convert what you have to what you want what you have to what you want to findto find unknown

unknownmoles

knowntcoefficienmoles

tcoefficienmolesmolesknown

)(

)(

Mole/Mole Mole/Mole StoichiometryStoichiometry

How many moles of aluminum are How many moles of aluminum are needed to form 3.7 moles of aluminum needed to form 3.7 moles of aluminum oxide?oxide?

____Al + ____O____Al + ____O22 → ____Al→ ____Al22OO33

How many moles of AlHow many moles of Al22OO33 are formed are formed when 0.78 moles of Owhen 0.78 moles of O22 reacts with reacts with aluminum?aluminum?

11.2 Calculations11.2 CalculationsMoles to MassMoles to Mass

Given the number of moles of a Given the number of moles of a reactant or product, we can calculate reactant or product, we can calculate the mass of another reactant or the mass of another reactant or product.product.

Use the mole ratio to convert from Use the mole ratio to convert from what you have to what you want to what you have to what you want to find.find.

Use the molar mass of what you want Use the molar mass of what you want to find to convert from moles to to find to convert from moles to grams.grams. known mole 1

known massmolar

known ficient)moles(coef

knownficient)moles(coefknown moles

un

unun

Moles to Mass PracticeMoles to Mass Practice

If 0.25 moles of TiOIf 0.25 moles of TiO22 are used, how are used, how many grams of Clmany grams of Cl22 are needed? are needed?

1TiO1TiO2 2 + 1C + 2Cl+ 1C + 2Cl2 2 1TiCl 1TiCl4 4 + CO+ CO22

Mole to massMole to mass

If 2.50 moles of NaCl are used, If 2.50 moles of NaCl are used, how many grams of Clhow many grams of Cl2 2 are are produced?produced?

2NaCl 2NaCl 2Na + 1Cl 2Na + 1Cl22

Mass to MassMass to Mass

Given the number of grams of a reactant or Given the number of grams of a reactant or product, we can calculate the number of product, we can calculate the number of grams of another reactant or product.grams of another reactant or product.

Use molar mass of what you have to convert Use molar mass of what you have to convert it to moles.it to moles.

The rest of the process is the same:The rest of the process is the same:– Use mole ratio to convert from what you have to Use mole ratio to convert from what you have to

what you need find.what you need find.– Use molar mass of what you need find to convert Use molar mass of what you need find to convert

your answer from moles to grams.your answer from moles to grams.

known mole 1

known massmolar

ownficient)knmoles(coef

knownficient)moles(coef

known massmolar

known mole 1known grams

un

unun

Mass to Mass PracticeMass to Mass Practice

2NaN2NaN3 3 2Na + 3N 2Na + 3N22

100.0 g ? g100.0 g ? g

2SO2SO2 2 + 1 O+ 1 O2 2 + 2H+ 2H22O O 2H 2H22SOSO44

2.50 g ? g2.50 g ? g

Volume and Particle Volume and Particle RelationshipsRelationships How many molecules of oxygen are How many molecules of oxygen are

produced by the decomposition of produced by the decomposition of 6.54g of potassium chlorate?6.54g of potassium chlorate?

How many liters of oxygen are How many liters of oxygen are required to burn 3.86L of carbon required to burn 3.86L of carbon monoxide?monoxide?

Mass RelationshipsMass Relationships

must obey the law of conservation of must obey the law of conservation of mass (moles aren’t equal, but mass mass (moles aren’t equal, but mass must be the same on both sides)must be the same on both sides)

What mass of oxygen, OWhat mass of oxygen, O22, is required , is required to completely combust 454 g of to completely combust 454 g of propane, Cpropane, C33HH88? What masses of CO? What masses of CO22 and Hand H22O are produced?O are produced?

CC33HH88 + 5O + 5O22 3CO 3CO22 + 4H + 4H22OO

More Mass Practice…More Mass Practice…

CaCCaC22 + 2H + 2H22O O C C22HH22 + Ca(OH) + Ca(OH)22

How many grams of CHow many grams of C22HH22 are are produced by adding water to produced by adding water to 5.00g CaC5.00g CaC22??

How many moles of CaCHow many moles of CaC22 are are needed to react completely with needed to react completely with 49.0g H49.0g H22O?O?

11.3 Limiting 11.3 Limiting ReactantsReactants A limiting reactant determines the amount A limiting reactant determines the amount

of product formed. of product formed. – 1. Start with a balanced chemical equation.1. Start with a balanced chemical equation.– 2. Identify what you have for each reactant.2. Identify what you have for each reactant.– 3. Convert what you have to moles.3. Convert what you have to moles.– 4. Calculate the ratio of available moles of each 4. Calculate the ratio of available moles of each

reactant. (what you have)reactant. (what you have)– 5. Use the balanced chemical equation to 5. Use the balanced chemical equation to

calculate the ratio of moles of each reactant calculate the ratio of moles of each reactant (what you need)(what you need)

– 6. For each reactant, do you 6. For each reactant, do you havehave more or less more or less than what you than what you needneed??

Limiting ReactantLimiting Reactant1.1. 6Na + 1Fe6Na + 1Fe22OO3 3 3Na 3Na22O + 2FeO + 2Fe2.2. 100.0 g 100.0 g100.0 g 100.0 g3.3. ..

4.4. ..5.5. ..

6.6. We have 6.94 mol Na; we need 6 mol. Na is in We have 6.94 mol Na; we need 6 mol. Na is in excess. We have 1 mol Feexcess. We have 1 mol Fe22OO33; we need 1 mol. ; we need 1 mol. FeFe22OO33 will run out first. will run out first.

3232

3232 OFe moles 62.0

OFe g 7.159

OFe mole 1OFe g 100.0

Na moles 35.4Na g 22.99

Na mole 1Na g 0.100

)( OFe mol 1

Na mol 94.6

OFe mol 62.0

Na mol 35.4

3232

HAVE

)(OFe mol 1

Na mol 6

32

NEED

Limiting ReactantsLimiting Reactants

CC22HH44 +3O +3O22 2CO 2CO22 + 2H + 2H22OO

If 2.70mol CIf 2.70mol C22HH44 is reacted with 6.30 is reacted with 6.30 mol Omol O22; identify the limiting reactant.; identify the limiting reactant.

Identify the limiting reactant if 2.70 Identify the limiting reactant if 2.70 mol Cmol C22HH44 is reacted with 6.30 mol O is reacted with 6.30 mol O22..

Limiting ReactantsLimiting Reactants

Pure silicon, required for computer Pure silicon, required for computer chips and solar cells, is made by chips and solar cells, is made by the reactionthe reaction

SiClSiCl44 + 2Mg + 2Mg Si + 2MgCl Si + 2MgCl22

If you begin with 225 g each of SiClIf you begin with 225 g each of SiCl44 and Mg, which is the limiting and Mg, which is the limiting reactant in this reaction? What reactant in this reaction? What quantity of Si, in grams, can be quantity of Si, in grams, can be produced?produced?

11.4 Percent Yield11.4 Percent Yield

The ratio of the actual yield The ratio of the actual yield (formed in lab) to the theoretical (formed in lab) to the theoretical yield (max amount that could be yield (max amount that could be formed)formed)

100ns)calculatio tricstoichiome (from yield ltheoretica

)experimentan (from yield actual yieldpercent

Percent YieldPercent Yield

When 84.8g of iron (III) oxide When 84.8g of iron (III) oxide reacts with an excess of carbon reacts with an excess of carbon monoxide, 54.3g of iron is monoxide, 54.3g of iron is produced. What is the percent produced. What is the percent yield?yield?

Percent YieldPercent Yield

Methanol, CHMethanol, CH33OH, can be burned in OH, can be burned in oxygen to provide energy, or it can be oxygen to provide energy, or it can be decomposed to form hydrogen gas, decomposed to form hydrogen gas, which can then be used as a fuel.which can then be used as a fuel.

CHCH33OH OH 2H 2H22 + CO + CO

If 125 g of methanol is decomposed, what If 125 g of methanol is decomposed, what is the theoretical yield of hydrogen? If is the theoretical yield of hydrogen? If only 13.6 g of hydrogen is obtained, only 13.6 g of hydrogen is obtained, what is the percent yield of the gas?what is the percent yield of the gas?