Mole Review

1.) Calculate the number of moles in 60.4L of O2.

2.) How many moles are there in 63.2g of Cl2?

60.4L O2

22.4L O2

1 mol O2 = 2.7 mol O2

63.2g Cl2

70g Cl2

1mol Cl2 = 0.903mol Cl2

Unit 08

Math In Chemistry

Stoichiometry

Tiny Tyke Tricycle Company

F + S + 3W + H + 2P → FSW3HP2

Scheduled to make 640 tricycles. How many wheels should they order?

Proportional Relationships

Proportional Relationships

I have 5 eggs. How many cookies can I make?

3/4 c. brown sugar1 tsp vanilla extract2 eggs2 c. chocolate chipsMakes 5 dozen cookies.

2 1/4 c. flour1 tsp. baking soda1 tsp. salt1 c. butter3/4 c. sugar

5 eggs 5 doz.2 eggs = 12.5 dozen cookies

Ratio of eggs to cookies

Proportional Relationships• Stoichiometry– mass relationships between substances in a

chemical reaction• for example: you can determine the amount of a

compound required to make another compound– based on the mole ratio

• Mole Ratio– indicated by coefficients in a balanced equation

2 Mg + O2 2 MgO2 Moles of magnesium react with 1 mole of oxygen to form 2

moles of magnesium oxide.

2 Mg + O2 2 MgO

What would be the mole ratio of magnesium to magnesium oxide?

2 : 2Conversion factor = 2 mol Mg

2 mol MgO What would be the mole ratio of oxygen to

magnesium?1 : 2

Conversion factor = 1 mol O2

(Mole Ratio) 2 mol Mg

Practice

5 F2 + 2NH3 N2F4 + 6HF1. What is the mole ratio of NH3 to F2? Write the mole ratio as a conversion factor.

2. What is the mole ratio of HF to N2F4?Write the mole ratio as a conversion factor.

2:5

2mol NH3

5mol F26:1

6mol HF1mol N2F4

Stoichiometry Steps

1. Identify known & unknown.2. Convert known to mole. (if necessary)3. Use Mole Ratio.4. Convert moles to unknown unit. (if

necessary)

known

Mol of known

Mol of unknown

Mole ratio- get from equation

Mol of unknown

Units of unknown

Mass-Mass Stoichiometry

• Mass of reactants equals the products• Law of Conservation of Mass• ONLY mass and atoms are conserved in every

chemical reaction

Known g 1 mol Known

Molar massKnown

mol unknown

mol known

Mol ratio- get from equation

Molar mass unknown

1 mol unknown

Mass-Mass Stoichiometry

#1

The reaction of fluorine with ammonia produces dinitrogen tetrafluoride and hydrogen fluoride.

5F2 + 2 NH3 → N2F4 + 6HF

How many grams of NH3 are required to produce 7.38g HF?

Mass-Mass Stoichiometry

#2

5F2 + 2 NH3 → N2F4 + 6HF

How many grams of N2F4 can be produced from 265g F2?

Mass-Mass Stoichiometry

#3

2C2H2 + 5O2 → 4CO2 + 2H2O

How many grams of oxygen are required to burn 52.0g C2H2?

• Calculate the number of grams of NH3 produced by the reaction of 5.40 g of hydrogen with an excess of nitrogen.

N2 + 3H2 → 2NH3

C. Stoichiometry ProblemsC. Stoichiometry Problems

__S + __O2 → __SO3 Write the equation. Balance the equation. How many moles of SO3 are produced when

there are 4.5 moles of S? Known = Unknown =

Mole-Mole Examples

#1

2C3H7OH + 9O2 → 6CO2 + 8H2O Write the equation. Calculate the moles of oxygen needed to

react with 3.40 moles of isopropyl alcohol.

Mole-Mole Examples#2

Isopropyl alcohol (C3H7OH) burns in the air to this equation:

2C3H7OH + 9O2 → 6CO2 + 8H2O

Find the moles of water when 6.20 mol O2 reacts with C3H7OH.

Mole-Mole Examples

#3

Volume-Volume Stoichiometry

• Formula to use:

Known (L) 1 mol known mol unknown 22.44 L unknown 1 22.4 L known mol known 1 mol unknown

C3H8 + 5O2 → 3CO2 + 4H2O

If 20 liters of oxygen are consumed in the above reaction, how many liters of carbon dioxide are produced?

Volume Example

#4

Limiting Reactants/Reagents

• Available Ingredients– 4 slices of bread– 1 jar of peanut butter– 1/2 jar of jelly

Limiting Reactant/Reagents bread

Excess Reactants/Reagents peanut butter and jelly

Limiting Reactants/Reagents

• Limiting Reactant/Reagent– used up in a reaction– determines the amount of product

• Excess Reactant/Reagent– added to ensure that the other reactant is

completely used up– cheaper & easier to recycle

Limiting Reagents

1. Write a balanced equation.

2. For each reactant, calculate the amount of product formed.

3. Smaller answer indicates:– limiting reactant– amount of product

Limiting Reagents

79.1 g of zinc react with 0.90 L of HCl. Identify the limiting and excess reactants. How many liters of hydrogen are formed at STP?

Zn + 2HCl ZnCl2 + H2 79.1 g ? L0.90 L

Limiting Reagents

79.1g Zn

1 molZn

65g Zn

= 27.3 L H2

1 molH2

1 molZn

22.4 LH2

1 molH2

Zn + 2HCl ZnCl2 + H2 79.1 g ? L0.90 L

Limiting Reagents

0.90L HCl

1 molHCl

22.4

L HCl

= 0.45 L H2

1 molH2

2 molHCL

22.4 LH2

1 molH2

Zn + 2HCl ZnCl2 + H2 79.1 g ? L0.90 L

Limiting Reagents

Zn: 27.3 L H2 HCl: 0.45 L H2

Limiting reagent: HCl

Excess reagent: Zn

Percent Yield

• Percent yield- the ratio of the actual yield to the theoretical yield

• Actual yield- the amount of product formed when a reaction is carried out in the laboratory

• Theoretical yield- the calculated amount of product formed during a reaction

Percent Yield

100yield ltheoretica

yield actualyield %

calculated on paper

measured in lab

Percent Yield

• When 45.8 g of K2CO3 react with excess HCl, 46.3 g of KCl are formed. Calculate the theoretical and % yields of KCl.

K2CO3 + 2HCl 2KCl + H2O + CO2

45.8 g ? g

actual: 46.3 g

Mole - MoleKnown mol of unknown

mol of known

Mol Ratio – from equationMass - Mass

Known g

molar mass known

1 mol known mol of unknown

mol of known 1 mol unknown

molar mass unknown

Known L

22.4 L known

1 mol known mol of unknown

mol of known 1 mol unknown

22.4 L unknown

particles

6.02 × 1023 particles

6.02 × 1023 particles

OROR

OR

Other

Formulas to Use