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STOY-KEE-AHM-EH-TREE

Stoichiometry is the part of chemistry that studies amounts of substances that are involved in reactions.

GOALSGOALS2

2. Explain the role of equilibrium in chemical

reactions

1. Demonstrate the conceptual principle of limiting reactants.

3. Identify and solve different types of stoichiometry problems,

specifically relating mass to moles and mass to mass.

The Mole Song- A Review

Moles & Molar Mass Review• 1 mole is _______ atoms/molecules• How many atoms are in 1.5 moles of neon?

• Calculate the number of grams in 3.25-mol of AgNO3

• How many moles are there in 250.0 grams of sodium phosphate (Na3PO4)?

• How many grams are in 5.6 x 1023 atoms of Zinc?

Before we start…let’s review…..

1.5mol

1x

6.02x1023atoms

1mol9.0x1023atoms

250g

1x

1mol

164g1.52mol

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Practice with a Friend 1. What is the mass of 7.50 moles of

sulfur dioxide (SO2)?

2. How many moles are there in 21.4 grams of nitrogen gas (N2)?

3. How many moles are there in 250.0 grams of sodium phosphate (Na3PO4)?

4. How many calcium atoms would be in a 100 gram sample of calcium metal?

5. Find the mass in grams of 7.5 1015 atoms of nickel.

7.5mol

1x

64g

1mol480g

21.4g

1x

1mol

28g0.764mol

250g

1x

1mol

164g1.52mol

100g

1x

1mol

40gx

6.02x1023atoms

1mol1.5x1024 atoms

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2HCl + Ba(OH)2 2H2O + BaCl2 1 1

coefficients give MOLAR RATIOS

Stoichiometry• Stoichiometry

– is the calculation of relative quantities of reactants and products in chemical reactions

– helps you figure out how much of a compound you will need, or maybe how much you started with.

“amounts of substances that are

involved in reactions”

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What are some molar ratio we can write from this equation?

Stoichiometry“amounts of

substances that are involved in reactions”

What do we know from this equation?

there is: one mole of CH4 for every two moles of H2Othere is: one mole of CH4 for every one mole of CO2

there are: 2 molecules of O2 for every one molecule of CO2

there are even: four atoms of H in CH4 for every two atoms of O in 2H2O

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How can we write these as conversion factors?

Stoichiometry

CH4 + 2O2 CO2 + 2H2O there is: one mole of CH4 for every two moles of H2O

there are: 2 molecules of O2 for every one molecule of CO2

there are even: four atoms of H in CH4 for every two atoms of O in 2H2O

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1) C3H8 + 5O2 3CO2 + 4H2OWhat do we know from the balanced equation?

• 1 molecule of propane for every 3 molecules of CO2

• 3 atoms of C in propane for 4 molecules of water• 9 atoms of hydrogen in propane for 8 atoms of hydrogen in water

http://laude.cm.utexas.edu/courses/ch301/lecture/ln2rf07.pdf

2) Fe + S FeS       What do we know from the balanced equation?         1 atom  of Fe   +   1 atom  of S  ---->   1 molecule of FeS                 10 atoms of Fe  + 10 atoms of S ----> 10 molecules of FeS 55.8 mg of Fe  +      32.1 mg S  ---->   87.9 mg  FeS 5.58 g of Fe     +      3.21 g of S ----> 8.79 g of FeS

Now you try: Write as many conversion factors as you can

Stoichiometry8

Our goal..To be able to determine amounts of products and reactants…moles

and grams….for ANY chemical reaction.

• Cutesy….but GOOD… video clip about mole conversions.

• After this video, we will now have a class rule about all conversions….

• You must go through………

2 CH3OH (l) + 3 O2 (g) --> 2 CO2 (g) + 4 H2O (l)

• In the lab, you can’t work with single atoms or molecules. So, it is useful to be able to identify how many moles of one substance you need to make a certain amount of another substance.

Mole to Mole 9

N2 + 3H2 → 2NH3 

How many moles of hydrogen are needed to completely react with 2.0 moles of nitrogen?

2KClO3 → 2KCl + 3O2

How many moles of oxygen are produced by the decomposition of 6.0 moles of potassium chlorate?

Mole to Mole Practice• Carbon disulfide is an important industrial

solvent. It is prepared by the reaction of carbon with sulfur dioxide:

5C(s) + 2SO2(g) ----> CS2(s) + 4CO(g)

• How many moles of CS2 form when 6.3 mol of C reacts?

• How many moles of carbon are needed to react with 7.24 moles of SO2? molC

molSO

molCx

molSO18

2

5

1

2.7

2

2

10

22 26.1

5

1

1

3.6molCS

molC

molCSx

molC

Mole to Mole Practice

Silver can be made according to the following equation:

2AgNO3+ Ca Ca(NO3)2 + 2Ag

-If 35.3 moles of silver nitrate are reacted how many moles of silver are produced?

5.3gAgNO3

1x

2molAg

2molAgNO3

35.3molAg

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Mole to Mole Practice with a Friend

Use the following equation to answer the questions below:

2 CH3OH (l) + 3 O2 (g) --> 2 CO2 (g) + 4 H2O (l)

1.How many moles of water will be produced from the combustion of 0.27 moles of CH3OH?

2.How many moles of O2 are needed to burn 2.56 moles of CH3OH?

3.How many moles of CO2 are produced from the combustion of 5.25 moles of CH3OH?

4.How many moles of water are produced when 3.25 moles of CO2 are formed?

0.54 mol H2O

3.84 mol O2

5.25 mol CO2

6.50 mol H2O

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When N2O5 is heated, it decomposes:

2N2O5(g) 4NO2(g) + O2(g)

5. How many moles of NO2 can be produced from 4.3 moles of N2O5?

= moles NO2

4.3 mol N2O5

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2

ON mol2

NO mol48.6

6.How many moles of O2 can be produced from 4.3 moles of N2O5?

= moles O2

4.3 mol N2O5

52

2

ON 2mol

O mol12.2

Mole to Mole Practice with a Friend13

Mass to Moles/ Moles to Mass14

2 KClO3 ---> 2 KCl + 3 O2

• 1.50 mol of KClO3 decomposes.

– How many grams of O2 will be produced?

• (1.50 mol of KClO3/1) x (3 O2/2 mol of

KClO3) x (32g / 1 mol O2) = 72 g

1.5 mol KCLO3

3

2

2

3

molKCLO

Omol 15.99g O2

1 Mol O2

• If 80.0 grams of O2 was produced, how many moles of KClO3 decomposed?

• We want to produce 2.75 mol of KCl. How many grams of KClO3 would be required?

Mass to Moles/ Moles to Mass2 KClO3 ---> 2 KCl + 3 O2

337 g of KClO3

337 g of KClO3

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Practice with a friend

1) How many grams of H2O are produced when 2.50 moles of oxygen are used?

2) If 3.00 moles of H2O are produced, how

many grams of oxygen must be consumed?

3) How many moles of Li required to make 46.4 g of Li3N?

Mass to Moles/ Moles to Mass

2 H2 + O2 ---> 2 H2O

90 g of H2O

48 g of O2

6 Li(s) + N2(g) 2 Li3N(s)

46.4 g Li3N x (1 mol Li3N/34.8 g Li3N) x (6 mol Li/2 mol Li3N) = 4.00 mol Li

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Mass to Moles/ Moles to Mass_Pb(NO3)2+ _KI_PbI2+_KNO3

4. How many grams of Pb(NO3)2 are needed to react completely with 9.00 mol KI?

1490g Pb(NO3)2

_CH4 + _O2 _CO2+_H2O

0.81 mol O2

5. How many moles of water will be produced when 8.5 g of CH4 react with oxygen?

6. How many moles of N2O5 were used if 210g of NO2 were produced?

2N2O5(g) 4NO2(g) + O2(g)

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Mass to Moles/ Moles to Mass7. 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

8. Calculate the number of moles of ethane (C2H6) needed to produce 10.0 g of water.

2 C2H6 + 7 O2 4 CO2 + 6 H20

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MgCl2 (aq) + 2 AgNO3 (aq) 2 AgCl (s) + Mg(NO3)2 (aq) How many grams of silver chloride could be produced by

the complete reaction of 19.7 g of magnesium chloride with silver nitrate? 

Mass to Mass

4 FeS2 + 11 O2 → 2 Fe2O3 + 8 SO2 If iron pyrite, FeS2, is not removed from coal, oxygen from the air will combine with both the iron and the sulfur as coal burns. If a furnace burns an amount of coal containing 125 g of FeS2, how many grams of SO2 (an air pollutant) is produced?

Std Dev Mass-Mass conversions video

clip19

Mass TO MassHow many grams of water can I make from 25 grams of hydrogen gas and an excess of oxygen gas, using the reaction

•2 H2 + O2 2 H2O

225 grams of water

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Mass to Mass Practice 1. How many grams of CO2 will be produced by

the combustion of 15.0 g of propane? C3H8 (g) + 5 O2 (g) --> 3 CO2 (g) + 4 H2O (l)

2. How many grams of HCl are needed to react with 27.62 g of Fe2O3?

Fe2O3 (s) + 6 HCl (g) --> 2 FeCl3 (s) + 3 H2O (g)

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2N2O5(g) 4NO2(g) + O2(g)

3. How many grams of N2O5 are needed to produce 75.0 grams of O2?

4. Calculate how many grams of ammonia are produced when you react 2.00g of nitrogen with excess hydrogen.N2 + 3 H2 2 NH3

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6. During its combustion, ethane C2H6, combines with oxygen O2 to give carbon dioxide and water.  A sample of ethane was burned completely and the water that formed has a mass of 1.61 grams.  How many grams of ethane was in the sample?

0.90 grams of ethane

2 C2H6    +  7 O2   ----->  4  CO2   +  6  H2O

2Al(s) + 6HCl(aq) 2AlCl3(aq) + 3H2(g)

5. How many grams of aluminum chloride can be produced when 3.45 grams of aluminum are reacted with an excess of hydrochloric acid?

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Limiting Reactants• Limiting Reactant - The

reactant in a chemical reaction that limits the amount of product that can be formed.  The reaction will stop when all of the limiting reactant is consumed.

Goal: Demonstrate the conceptual principle of limiting reactants

Example: I want to assemble a gadget that requires one nut, one bolt and two washers for every hole. I have in my garage a bucket filled with 12 washers, 4 bolts and five nuts. What is the LIMITING SMALL METAL OBJECT?

Download/Link Std Dev mod 7

limiting reactant

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Example 1:You combine 10.0 grams of hydrogen gas and 15.0 grams of oxygen gas. How many grams of water vapor are made? Which is the limiting reactant?

Limiting Reactants Calculations

2H2 + O2 2H2O

http://www.lynden.wednet.edu/cms/lib02/WA01001013/Centricity/Domain/93/Chemistry%20Text/Limiting%20Reactant%20Problems%20text.pdf

Oxygen is limiting reactant, as the amount of H2O is much less than that produced by hydrogen.

How To…1-Calculate how much can be made by both.The one with the least amount is the LR.

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Example 2:If 5.00 grams of copper metal react with a solution containing 20.0 grams of AgNO3, which reactant is limiting and what mass silver is produced? A copper (II) product is formed.

Limiting Reactants How To…1-Calculate how much can be made by both.The one with the least amount is the LR.

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1) 10.0g of aluminum reacts with 35.0 grams of chlorine gas to produce aluminum chloride. Which reactant is limiting?

2 Al + 3 Cl2 2 AlCl3

CaO + 2HCl → CaCl2 + H2O 2)75 grams of calcium oxide react with 130 grams of hydrochloric acid to produce a salt and water. What is the

limiting reactant?  

Limiting Reactants-Practice with a friend

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Limiting Reactants-Practice with a friend

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3) 5g of copper metal react with a solution containing 20g of silver nitrate to produce copper (II) nitrate and silver.

Cu (s) + 2AgNO3 (aq) → Cu(NO3)2 (aq) + 2Ag (s)

4) 15.00 g of aluminum sulfide and 10.00 g of water react until the limiting reagent is consumed.

Al2S3 + 6 H2O → 2 Al(OH)3 + 3 H2S

Reversible Reactions• A reversible reaction is one

in which the conversion of reactants to products and the conversion of products to reactants occur simultaneously.

• Most reactions are reversible. Some are not-

• EX: • burning, • combustion.

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Equilibrium

• At equilibrium, the concentration of all reactants and products stays constant.

Std Dev Dynamic

Equilibrium

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• It seems as if nothing is happening, because the macroscopic properties, those you can see (e.g. color and temperature), do not change. However, at the microscopic level there is continual change.

• No “NET” change occurs.

• It is a DYNAMIC STATE Note: When the concentration of products stays constant and the concentration of reactants stays constant, the system is at equilibrium.

Dynamic Equilibrium31

• Amounts are not always 50/50 at equilibrium.

• Depends on which one is more favorable (products or reactants)

• Equilibrium refers mainly to the RATE of the reaction. Not the amounts of product and reactant.

Dynamic Equilibrium32

Factors Affecting Equilibrium:

• Le Chatelier’s Principle– If stress is applied to a

system in equilibrium, the system changes in a way that relieves the stress.

1.Adding more reactant or product

2.Change the temperature

3.Change the PressureLe Chatelier’s

Principle Video Clip

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35

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Baking Soda Lab

Video

Questions we could ask about the reaction….Question #1: How many CO molecules are required to react with 25 formula units of Fe2O3?

Fe2O3 + 3CO ----> 2Fe + 3CO2

Question #2. How many Fe atoms are produced by reaction of 2.5 x 105 formula units of Fe2O3 with excess CO?

Reaction of Stoichiometry Calculations

Question #3:What mass of CO is required to react with 146 grams of Fe2O3?

Fe2O3 + 3CO ----> 2Fe + 3CO2

Question #4:What mass of CO2 can be produced by the reaction of 0.540 moles of Fe2O3? …with excess CO?