Fire Unit Investigation II: Conditions for Change Lesson 1: No Smoking Zone Lesson 2: You’re...

Fire Unit

Investigation II: Conditions for ChangeLesson 1: No Smoking ZoneLesson 2: You’re Fired!Lesson 3: All-A-GlowLesson 4: Fuelish ChoicesLesson 5: SparklersLesson 6: Kablooie!

Fire Unit – Investigation II

Lesson 1:

No Smoking Zone

Unit V • Investigation II

© 2004 Key Curriculum Press.

ChemCatalyst

• What conditions are necessary for a fire to take place? Describe at least two situations that result in fire.



The Big Question

• What are the necessary questions for fire to exist?



You will be able to:

• Describe the conditions necessary to support a fire.



Activity

Purpose: By observing a series of demonstrations you will explore the conditions that lead to fire.

(cont.)



Demonstration Prediction

What will you observe

when lit?

Observation

Smoking machine

Paper

Wet paper (paper + water)

Drunk paper(paper + isopropanol)

Dollar bill(dollar+water+isopropanol)

Carbon dioxide balloon

(cont.)



Making Sense

Pick three things from the list below to build a fire. Explain your choices.

• water

• aluminum

• helium

• sugar

• oxygen

• wax

• match

• coal



Notes

(cont.)



• Combustion reaction: The reaction of a fuel with oxygen, resulting in the production of heat and light.

(cont.)



Check-In

• There is a small fire in the trashcan in your classroom. Name three things your teacher can do to put out the fire. Explain how each method works.



Wrap-Up

• Combustion is defined as a reaction of a fuel with oxygen, which releases heat and light.

• Dry fuel, a spark of some sort, and oxygen are the three items necessary for combustion.

• Limiting the supply of oxygen, or adding water, extinguishes fires.

(cont.)



• Cigarette smoking is a form of combustion that has many by-products, several of them harmful to your health.

(cont.)


Lesson 2:

You’re Fired!



ChemCatalyst

• Name three substances that will combust or burn.

• Name three substances that do not combust.



The Big Question

• How can we predict whether or not a substance is combustible?




• Identify several properties that help us determine whether a substance will be combustible or not.



Activity

Purpose: The goal of this lesson is to allow you to make generalizations about substances that combust and substances that do not combust.

(cont.)



Substance Chemical Formula Type of Bond Combust?

Water H2O molecular covalent no

Wood chains of C6H12O6 units extended covalent yes

Baking soda NaHCO3ionic no

Ethanol CH3CH2OH yes

Zinc oxide ZnO no

Copper Cu metal yes

Hexane CH3CH2CH2CH2CH2CH3yes

Magnesium Mg yes

Carbon dioxide

CO2no

Hydrogen H2yes

Helium He no



Substance Chemical Formula Combust?

(prediction)

Combust?

(outcome)

Oil C21H39O6 (one example)

Sodium chloride NaCl

Calcium carbonate

CaCO3

Iron Fe

(cont.)



Making Sense

• Based on your data, what generalizations can you make about substances that combust?

• What generalizations can you make about substances that do not combust?



Combust Do Not Combust

CH3CH2CH2OH

C6H12O6 units (wood)

CH3CH2OH

CH3CH2CH2CH2CH2 CH3

C21H39O6 (one example)

H2

Cu

Fe

Mg

H2O

CO2

ZnO

NaHCO3

NaCl

CaCO3

Notes

(cont.)



• Most ionic compounds are not combustible.

• Most molecular covalent compounds are combustible (especially those that contain carbon and hydrogen). These compounds make good fuels.

• Most metallic compounds are combustible.

(cont.)

(cont.)



• Substances that contain a high percentage of oxygen atoms may not be combustible because they may not be able to react with any more oxygen.

• Water and carbon dioxide do not combust.

(cont.)



Check-In

Which of the following substances are likely to combust? What is your reasoning?

• CH4, methane

• CaBr2, calcium bromide

• Na, sodium



Wrap-Up• Most ionic salts do not combust.

• Most molecular covalent compounds do combust.

• Most metals combust. Most metals do not produce a flame when they combust. Most metals combust very slowly.

• Substances that already contain a high percentage of oxygen atoms are less apt to be combustible.

• Carbon dioxide and water do not combust. They are the products of combustion.


Lesson 3:

All-A-Glow



ChemCatalyst

The following table shows the balanced chemical equations for four combustion reactions.

• List three patterns you notice.

Substance Combustion reaction

methane CH4 + 2 O2 CO2 + 2 H2O

ethanol C2H6O + 3 O2 2 CO2 + 3 H2O

glucose C6H12O6 + 6 O2 6 CO2 + 6 H2O

magnesium 2 Mg + O2 2 MgO



The Big Question

• How do we write a chemical equation for a combustion reaction?




• Write the balanced equations for various kinds of combustion reactions.



C2H6 + O2 CO2 + H2O

Notes



Activity

Purpose: The goal of this lesson is to allow you to examine chemical equations that describe combustion reactions.

(cont.)



Combustion Reactions of Alkanes

methane CH4 + 2 O2 CO2 + 2 H2O

ethane C2H6 + 3.5 O2 2 CO2 + 3 H2O

propane C3H8 + O2 CO2 + H2O

butane C4H10 + O2 CO2 + H2O

pentane C5H12 + O2 CO2 + H2O

hexane C6H14 + 9.5 O2 6 CO2 + 7 H2O

(cont.)

(cont.)



Combustion Reactions of Carbon and Carbon-Containing Molecules

methane CH4 + 2 O2 CO2 + 2H2O

methanol CH4O + O2 CO2 + H2O

carbon C + 1 O2 CO2

carbon monoxide CO + 0.5O2 CO2

carbon dioxide CO2 + 0 O2 no reaction

(cont.)

(cont.)



Combustion Reactions with Metals

magnesium Mg + 0.5 O2 MgO

magnesium oxide MgO + 0 O2 no reaction

magnesium chloride MgCl2 + 0 O2 no reaction

titanium Ti + 1 O2 TiO2

titanium oxide TiO2 + 0 O2 no reaction

titanium fluoride TiF4 + 0 O2 no reaction

(cont.)



Making Sense

• What are the products of the combustion of carbon-containing molecules?

• What are the products of the combustion of metals?

• What are the products of the combustion of salts?



Check-In

Pick a substance that combusts from the list below and write the balanced chemical reaction.

• Ar

• Al

• C

• CH4O



Wrap-Up

• The products of the combustion of carbon-containing molecules are carbon dioxide and water.

• Flames are gases emitting light. Flames are the result of gases that are produced during a combustion reaction.

(cont.)



• In a combustion reaction, the longer the carbon chain in the fuel, the more oxygen it reacts with.

• The products of the combustion of metals are solid metal oxides. These reactions usually do not produce enough gases to support a flame.

(cont.)


Lesson 4:

Fuelish Choices



ChemCatalyst

Standard automobiles use a mix of carbon-based compounds (high in octane) as fuel. The cars that race in the Indianapolis 500 use methanol as fuel. And top dragsters use nitromethane as fuel.

• Balance the equations for the combustion of these fuels.

• Why do you think they use different fuels for different types of driving?



(Below are the balanced chemical equations for these combustion reactions):

(octane)

C8H18 + O2 CO2 + H2O

(methanol)

CH4O + O2 CO2 + H2O

(nitromethane)

CH3NO2 + O2 CO2 + H2O + NO2

Notes



The Big Question

• What properties of a substance can be used to predict its usefulness as a fuel for combustion?




• Identify the properties of substances that would make them good fuels for combustion.



Activity

Purpose: In this activity, you will compare fuels to one another by examining their combustion reactions and calorie output.

(cont.)



Combustion Reactions

Substance Chemical Formula

Energy (cal/mole)

Chemical Reaction

Octane C8H18 (l)1,300,000 2 C8H18 + 25 O2 16 CO2 + 18 H2O

Hexane C6H14 (l)995,000 2 C6H14 + 19 O2 12 CO2 + 14 H2O

Hexanol C6H14O (l)951,000 2 C6H14O + 18O2 12 CO2 + 14 H2O

Butane C4H10 (l)687,000 2 C4H10 + 13 O2 8 CO2 + 10 H2O

Butanol C4H10O (l)638,000 C4H10O + 6 O2 4 CO2 + 5 H2O

Ethane C2H6 (g)373,000 2 C2H6 + 7 O2 4 CO2 + 6 H2O

Ethanol C2H6O (l)327,000 C2H6O + 3 O2 2 CO2 + 3 H2O

Methane CH4 (g)213,000 CH4 + 2 O2 CO2 + 2 H2O

Methanol CH4O (l)174,000 2 CH4O + 3 O2 2 CO2 + 4 H2O

Nitromethane

CH3NO2 (l)175,000 4 CH3NO2 + 7 O2 4 CO2 + 6 H2O + 4

NO2

Hydrogen H2 (g)58,000 2 H2 + O2 2 H2O



Substance Chemical Formula

Energy kcal/mol

Mol. Wt.

g/mol

Energy kcal/gram

Octane C8H18 1,300 114 11.4

Hexane C6H14 995 86 11.5

Hexanol C6H14O

Butane C4H10 58

Butanol C4H10O 638 74

Ethane C2H6 373

Ethanol C2H6O 46

Methane CH4 213

Methanol CH4O 32 5.4

Hydrogen H2 58

Nitromethane CH3NO2 61



Making Sense

• Do you think the best fuel is the one that has the greatest energy output in calories per mole? Explain your reasoning.



• kilocalories or kcal: 1 kcal is equal to 1000 calories. It is also equal to 1 food Calorie

• kiloJoule or kJ: 1 kJ is equal to 4.184 kcal. Joules are the metric units in common use by scientists.

Notes



Check-In

Which molecule of the three listed below would you expect to release the most energy per mole of fuel combusted? What is your reasoning?

• propane, C3H8

• propanol, C3H8O

• pentane, C5H12



Wrap-Up

• Substances consisting mostly of carbon and hydrogen atoms are good fuels.

• Trends show that the larger the carbon compound, the more energy is released per mole of fuel when that compound combusts.

• Molecules without oxygen atoms tend to release more energy than comparable molecules that contain oxygen (e.g., CH4 > CH3OH).

(cont.)



• The number of calories released during combustion is dependent on the size of the molecule.

• Chemists use kJoules as a unit of energy. One kcal = 4.184 kJoules.


Lesson 5:

Sparklers



ChemCatalyst

• I have several matches, a large tree trunk from a fallen tree, and plenty of oxygen in the atmosphere. Nevertheless, I cannot get the tree trunk to burn using just a lit match. If I have all three legs of the fire triangle, why is it difficult to make a fire?



The Big Question

• Once a combustion reaction has been started, what is it that keeps it going?




• Explain why a combustion reaction keeps on going even after the source of ignition has been removed.



Activity

Purpose: In this lesson you will create sparklers using several metals and several ionic compounds.

SAFETY NOTE: Remember to wear goggles during today's lab.

(cont.)



Substance Mass of watch glass + powder

(minus) Mass of

watch glass

(equals) Mass of powder needed

Starch 2.0 g

Iron powder (Fe) 3.3 g

Copper powder (Cu) 0.4 g

Magnesium powder (Mg) 0.2 g

Aluminum powder (Al) 0.7 g

Potassium chlorate (KClO3)

2.0 g

Barium nitrate (Ba(NO3)2) 8.3 g

(cont.)



Making Sense

• Why does a sparkler keep going after you light it? Why doesn't it go out?



Check-In

• No Check-In.



Wrap-Up

• The combustion of various metals can be used to create a colorful sparkler.

• There appears to be another condition necessary for fire, beyond the three legs of the fire triangle.


Lesson 6:

Kablooie!



ChemCatalyst

• What is an explosion?

• What causes explosions?

• Have you ever seen or experienced an explosion? Explain.



The Big Question

• What are the conditions that affect the rate of a combustion reaction?




• Explain how the rate of a combustion reaction is affected by the conditions in which it is occurring.



Activity

Purpose: In this lesson you will be allowed to test your sparkler. Then you will observe a series of demonstrations related to explosions. Finally, you will be introduced to the Fire Tetrahedron.

(cont.)



(cont.)

(cont.)



(cont.)



Making Sense

• What conditions appear to be necessary for an explosion to take place?



• An explosion is defined as the effect that occurs when there is a violent expansion of gases.

(cont.)

Notes



(cont.)



Check-In

• Explain what is meant by the statement, “Fuels with small molecular masses (such as CH3OH, methanol) burn better than fuels with large molecular masses (such as C8H14, octane).” Why do you think this is true?



Wrap-Up

• An explosion is a rapid expansion of gases.• Not all fires involve explosions.• Some explosions do not involve fire at all.• The surface area of a fuel, and the

availability of oxygen to the fuel, are factors that affect the rate of combustion.

• There are four conditions necessary for fire. These four conditions are represented in the fire tetrahedron: oxygen, fuel, heat (or spark), and chemical chain reaction.

Fire Unit Investigation II: Conditions for Change Lesson 1: No Smoking Zone Lesson 2: You’re...

Documents

Transcript of Fire Unit Investigation II: Conditions for Change Lesson 1: No Smoking Zone Lesson 2: You’re...