STOICHIOMETRY

Chapter 9

Mass-Mass

Stoichiomet

ry

Mole-Mole

Mass-Mole

Volume

Mixed mole

StoichiometryO Calculation of quantities in chemical

equationsO From Greek words

O Stoichion = elementO Metron = measure

Two types of Stoichiometry1. The mole relationships of elements in

compounds (empirical formulas)

H3PO4

2. The mole relationships of reactants and products in a chemical equations (balanced equations)

2 H2 + O2 2H2O

Chemical EquationsO All balanced equations are always based on

the units of the mole

N2 + 3 H2 2 NH3

Translated:1 mol N2 + 3 mol H2 2 mol NH3

Mole RatioO A conversion factor that relates the # of

moles of any two substances involved in a chemical reaction

O Comes from a balanced equation

5 Types of Stoichiometry problems

1. Mole-mole2. Mass-mass3. Volume-volume4. Particle-particle5. Mixed problems

1. mole-mole problemsO Moles of A moles of BO Mole ratio…

H2 + O2 H2O

• Balance it first!• How many moles of hydrogen do you

need to make 17 moles of water?

1. mole-mole problems – EX

2H2 + O2 2H2O

Given: 17 moles waterUnk: moles hydrogen?CF:Solve:

1. mole-mole problems – EX

2H2 + O2 2H2OHow many moles of oxygen will you

need to react with 334 moles of hydrogen?

1. mole-mole problems – EX

Blank Active Inspire for more

practice

2. Mass – mass problemsO Mass A Moles of A moles of B mass BO Mole ratio…

Al + O2 Al2O3Balance first!!!a) How many grams of aluminum do

you need to make 15 grams of aluminum oxide?

mass-mass problems – EX

Given: 15 g Al2O3

Unk: ? g AlCF: 2 mol Al2O3 : 4 mol Al

molar mass Al2O3 = 101.96 g/mol

molar mass Al = 26.98 g/mol

mass-mass problems – EX4Al + 3O2 2Al2O3

Blank Active Inspire for more

practice

3. volume-volume problemsO Volume A moles A moles B volume B

3. Volume-Volume EquationsN2 + H2 NH3

a) How many liters of hydrogen do you need to make 25 liters of ammonia?

3. Volume-Volume EqnsN2 + 3H2 2NH3

Given: 25 L NH3

Unk: ? L H2

CF: 2 mol NH3 : 3 mol H2

STP conversion = 22.4 L / 1 mol

Volume –p6

4. particle-particle problemsO Particles A moles A Moles B --.

Particles BO Mole ratio…

4. Particle-Particle EquationsN2 + H2 NH3

a) How many molecules of hydrogen are needed to react with 3.784x1025 molecules of ammonia?

4. Particle-Particle EqnsN2 + 3H2 2NH3

Given: 3.784x1025 mo NH3

Unk: ? mo H2

CF: 2 mol NH3 : 3 mol H2

Avo’s Number = 6.02x1023/1 mol

5. Mixed mole problems

O ? unit A moles A Moles B ? Unit BO Mole ratio…

5. Mixed Eqns

N2 + H2 NH3OWhat volume of ammonia at STP is

produced if 25 g of nitrogen is reacted with excess hydrogen?

5.Mixed EqnsN2 + 3H2 2NH3

• Given: 25 g N2

• Unknown: ? L NH3

• (mass-volume problem)• CF: 1 mol N2 : 2 mol NH3

Mixed-p10

Limiting Reagents and Percent Yield

Section 9.3

2 slices bread + 2 slices cheese = 1 grilled cheese sandwich

How Many Sandwiches?O If I have 12 slices bread?

O If I have 6 slices cheese?

O If I have 12 slices of bread and 6 slices of cheese?

The amount of cheese limits how many sandwiches you can make. All of it’s used!

Bread is in excess which means there is some bread left over.

Limiting ReagentO Limiting Reagent = The reactant that

limits the amount of products madeO Gets completely used up in a reaction

O Excess reagent = the reactant that is not used up completelyO There is more than enough leftover

Steps to determine LR & ER

1. Set up two mass-mass problems.

2. Compare the amounts of product.

3. Identify Limiting reagent = reactant that makes the least amount of product.

4. Determine how much ER is used based on the amount of LR given in a third mass-mass problem.

5. Subtract the amount of ER used from the given amount to determine how much ER is leftover.

EX: Limiting & Excess Reagents

C + O2 CO2

Complete two mass-mass problems with information given to determine limiting reagent

55 g

35 g

EX: Limiting & Excess Reagents

C + O2 CO2

Limiting Reagent = How much ER will you use?

How much ER leftover?

55 g

35 g

Page 11

Percent YieldO Used to determine how accurate a person is in

the labO Percent yield = actual yield X

100 theoretical yield

O Actual yield = the amount of product produced in the lab

O Theoretical yield = the amount of product that should have been produced in theory

EX; Percent YieldO What is the percent yield if John made 15.87

g of chalk and he calculated that he should have made 22.5 grams of chalk?O Actual yield = O Theoretical yield = O Percent yield =

END OF CHAPTER

QUESTIONSPage 262 # 36, 37, 38, 41, 42, 44,

45, 46