Fire!

Chem CatalystFired Up

Today you will be observing several different combustion reactions.

1.) What do you think a combustion reaction is?

2.) There are 3 general things needed for a combustion reaction to occur – what are they?

Fire Safety• Tie back long hair, which is especially

flammable when mixed with hair spray. Avoid loose clothing.

• Small fires may be extinguished by smothering flames with water, sand, or a fire blanket. A carbon dioxide fire extinguisher can be used to combat most fires, except fires caused by metals.

The Big Question

• What are the characteristics of fire?

Making Sense

• Changes in matter involve changes in energy.

• Exothermic process: A process that releases energy in the form of heat.

• Reactions of elements and compounds with oxygen typically are exothermic.

• Combustion requires oxygen.

Predict-Explain-Observe-Explain

• A strip of paper is dipped into a mixture of isopropyl alcohol (C3H8O) and water.

• Predict what will happen to the paper when it is lit on fire. Explain why you said what you said.

• Observe the demonstration.

• Explain what happened.

Chem CatalystNot So Hot

1. How do you think hand warmers work? Where does the heat come from?

Lab introduction

• You will be observing three chemical processes today. Focus on the heat transfer in each one.

• Work in groups of four.

• Follow directions at the three stations.

Preliminary Definition of Energy

• Energy: A measure of the work involved in moving or changing something.

Ex: changes in temperature

• Energy is not a substance (i.e. energy is NOT matter)

Definition of Heat

• Heat: A transfer of energy between two substances due to temperature differences.

• To look at heat, we have to define the system and surroundings.

System and Surroundings

• System: The process you are focusing on. In this case, a chemical reaction.

• Surroundings: Everything outside the system (thermometer, beaker, your body)

Definitions• Exothermic:- Feels warm- Gives off heat- Heat transfers from the reaction your hand

• Endothermic Reaction: - Feels cold- Absorbs heat- Heat transfers from your hand the reaction

Computer Simulation

• Molecular workbench: search “exothermic”, explosion.

• What is happening during an explosion? How is energy transferred?

Chem Catalyst

• Imagine you are sitting near a campfire. You feel warm.– Explain how you think burning wood

transfers heat to your body.– The next morning you find ashes that are

the same temperature as the air. Explain why the ashes are no longer hot.

ChemCatalyst

• You have water at 25ºC. You dissolve ammonium acetate, NH4C2H3O2, in the water and find that the temperature decreases to 17ºC.1.) Is the process exothermic or endothermic?

2.) How will it feel if you put your hand on it?

3.) In which direction is the heat transferring?

Purpose

• Today’s question: How do we consider energy transfer from different points of view?

Making Sense

Instructions for the water stations

Making Sense

• Was the lukewarm water at the water station hot or cold?

• Why did the lukewarm water feel hot to one hand and cold to the other?

• If you say something is “hot, what do you mean?

• If you say something is “cold,” what do you mean?

“Hot” and “Cold”

• For the rest of the Fire unit, we won’t say anything is “hot” or “cold.”

• Instead, we can say…

Definitions

• Heat (thermal energy) always transfers from the warmer object to the colder object.

• Thermal equilibrium: when two objects in contact with each other reach the same temperature.

Laws of Thermo

• First Law of Thermodynamics: Energy is conserved. (we can transfer energy, but you can’t create or destroy it)

• Second Law of Thermo: Energy tends to disperse - energy flows from objects of high temperatures to low temps.

Check-In

• Imagine that a thermometer is placed in a beaker of water and the temperature is noted. An ice cube is dropped into the water, and after ten minutes the temperature is noted again.– What will you observe?– What is the direction of energy transfer?

Chem Catalyst

• You are standing outside freezing with no gloves on for several minutes. You sneeze and get stuff all over your hands. When you come into the house, you turn on the cold faucet and start washing your hands. Why do your hands feel so hot under the water? Draw a picture of the direction of heat transfer.

Exercise

• Write two sentences, using proper English, that use the word “heat”.

• After you are done, identify the part of speech that you use “heat” as for both of your sentences.

ChemCatalyst• A thermometer is placed in a beaker of water

and the temperature is 21ºC. An ice cube is dropped into the water and after 10 minutes the temperature is 14ºC.

– Is this an endo or exothermic process?– What is the change in temperature?– Draw a picture showing the direction of heat

transfer.

Chem CatalystHeat versus Temperature

• Chemists talk about the “average kinetic energy” of molecules very often. What do you think this means?

• What chemistry tool could you use to measure the “average kinetic energy” of molecules?

Chem CatalystHeat versus Temperature

• A lead atom is moving at 40 mph. A hydrogen atom is also moving at 40 mph. Will they have the same temperature or different? Why?

• Priority #1 =

Finishing this assignment

• When you are finished, you can work on anything else that is appropriate.

Go to computer lab for Heat vs. Temp simulation

Chem CatalystHeat versus Temperature

• Write “1/2 day open note quiz” for your chem catalyst

• Take out any papers you want to use for the optional NeilMed quiz

• I will take whichever grade is higher – either your NeilMed project or the quiz

Recall:

• Thermal equilibrium is reached when two objects in contact with one another reach the same temperature.

Online Simulation

• http://jersey.uoregon.edu/vlab/Thermodynamics/index.html

• Experiments #1 and #5

Questions about the simulation

• What happens when you heat the gas atoms in the simulation?

• Are all the atoms moving at the same speed?

• What happens to the sample when you add atoms?

• How can you make the heat energy of the sample increase without increasing the temperature of the sample?

Heat vs. Temperature Lab

Making Sense

Key Points

• The final temperature of a mixture depends on mass and temperature of the samples.

• Are heat and temperature the same?

Definition

• Thermal Energy - The total kinetic energy associated with the mass and motions of the particles in a sample of matter.

Definition

• Calorie: The amount of energy it takes to raise the temperature of one gram of water by one degree Celsius.

• The equation for heat transfer in water is:

Sample problem

• How much heat transfer is required to raise the temperature of 5.0 g of water from 25ºC to 75ºC?

ChemCatalyst• GET A CALCULATOR PLEASE

• You have one beaker containing 500 g of water at 75ºC. You also have a beaker with 2000 g of water at the same temperature.

1.) Which will melt more ice? Explain your answer in terms of thermal energy, heat transfer, and temperature.

Discussion

• Does total energy depend on the amount of a substance?

• Does the temperature depend on the amount of a substance?

• What factors determine how much energy can be transferred from one object to another?

ChemCatalyst

1.) Come up to the front of the room and record the temp of both black objects.

2.) Touch both objects. Which do you think will melt an ice cube faster? Why?

3.) Observe what happens when an ice cube is placed on each.

Chem Catalyst• Imagine you are at the beach. The sun has

been shining all day long, and you want to go for a swim.

– How does the sand feel on your feet? How will the water feel?

– You go back out to the beach at night for a swim. How does the sand feel now? What about the water?

Chem Catalyst• Rank the following substances from coldest

to warmest in terms of how they will feel when you touch them.

Wood Metal Rubber Stopper

Candle Rock Plastic pipe

Explain your predictions, please.

Items from Lab

Which substances felt coldest?

Wood = 0.6 cal/g*ºCMetal = 0.092 cal/g*ºCRubber Stopper = 0.48 cal/g*ºCCandle = 0.7 cal/g*ºCPVC = 0.215 cal/g*ºCRock = 0.19 cal/g*ºC

NotesSpecific Heat Capacity (C):

The amount of energy (in calories) needed to raise the temperature of 1 gram of a substance by 1 degree Celsius

Different materials have different heat capacities

Specific heat capacity for water:

1.00 cal

g * ºC

In other words, it takes ____ calories to raise ___ grams of water by ____ degrees Celsius

NotesSubstances with Low Heat Capacity

- Transfer heat energy easily (good heat conductor)

- Heat up quickly

- Cool down quickly

Ex: Metals, rocks

Substances with High Heat Capacity- DO NOT transfer heat easily- Heat up slowly- Cool down slowly

Ex: Wood, Water

Class DemonstrationHow can you explain why the ice cube melted

faster on the black metal square? Use what you know about energy transfer and heat capacity.

Class DemonstrationFeel both black substances.

If an ice cube is placed on each substance, which will make it melt faster?

You have two unknown substances. They each have a temperature of 65 degrees F. The first substances has a heat capacity of 0.12 cal/g*C. The second substance has a heat capacity of 0.63 cal/g*C.

Which substance will melt ice faster and WHY?

ChemCatalyst

Calculating the amount of heat transferred

Heat = mass x specific heat capacity x temperature change

Heat = m•C •(Tfinal - Tinitial)

Notes• Since water requires more energy to raise its

temperature, we say that water has a higher heat capacity than ethanol.

• Let’s translate this to “regular English”

Cwater 1

cal

ggC Cethanol 0.58

cal

ggC

Notes

• How many calories does it take to raise the temp of 50 g of ethanol by 1ºC?

• How many calories does it take to raise the temp of 50 g of ethanol by 25ºC?

Cwater 1

cal

ggC Cethanol 0.58

cal

ggC

Practice Problems

• How many calories does it take to raise the temperature of 22 g of brass from 18.0 ºC to 25 ºC? The specific heat capacity of brass is 0.09 cal/g•ºC.

• How much does the temperature increase if you have a 6 g sample of brass and you add 690 calories of heat energy to it?

Notes

• Do you think metals have a higher or lower heat capacity than water? Explain. (Think about heating a pot of water on the stove. Which one heats up more quickly?)

Tomorrow’s Lab• You will be given an unknown metal. You will

have to identify the type of metal it is by determining it’s specific heat capacity.

• Materials:

- Styrofoam cup

- Water

- Scale (electronic balance)

- Thermometer

- Your metal at a known temperature

- Chart with specific heat capacity of metals

What do you need to know (or measure)?

ChemCatalyst

• Two students are debating how much water should be used in the lab today. Fernando says that you should use as little water as possible. Shaquanda says that you should use as much water as you can to fill the cup.

• Who has the better idea and why?

Check-In

• How many calories of energy are needed to raise the temperature of 32 g of aluminum by 23 degrees Celsius?

ChemCatalyst

• The first step of yesterday’s lab was to calculate the calories of energy transferred to the water.

1.) Why can we use this value when we calculate the specific heat of the metal?

2.) Why would it improve your results to stir the water when you drop in the metal?

Chem Catalyst

It’s a sunny day and you find a park bench. You’re wearing some shorts like the old-school basketball players used to wear and you go to sit on the bench.

1.) Do you sit on the metal parts or the wooden parts of the bench? Why?

Check-in• The specific heat capacity of aluminum

is 0.22 cal/gºC. • Translate the specific heat capacity to

English. • How much energy does it take to raise

10 g of aluminum by 10 degrees Celsius? How much energy does it take to raise 10 g of water by 10 degrees Celsius (the specific heat capcity of water s 1 cal/gºC)?

Chem CatalystGRAB A CALCULATOR

The specific heat of stainless steel is 0.12 cal/g*ºC. How many calories does it take to raise the temperature of 2.5 g of stainless steel from 25.0 ºC to 99.5 ºC?

Question of the day

• You have a piece of metal that is 100ºC and place it against another piece of metal that is 25ºC.

• What happens to the two pieces of metal over time?

• Describe how you think energy is transferred from one object to the other in terms of how the atoms are moving in both objects. Think about the “heat vs. temperature” simulation and how the fast and slow molecules transferred energy.

Whiteboarding• With a group of 3, whiteboard the following:• Draw molecular pictures of two solids separated

by a space.• The solid on the left has a higher average kinetic

energy than the solid on the right. (what does that mean in terms of their temperatures?)

QuickTime™ and aTIFF (LZW) decompressor

are needed to see this picture.

Whiteboarding continued…

• In three separate pictures, show how the heat is conducted (transferred) from one object to another if the following items were placed between the two solids: another solid, a liquid, or a gas.

• Be able to answer the question “Which object conducts energy better and why?”

QuickTime™ and aTIFF (LZW) decompressor

are needed to see this picture.

Myers, Alexis 1Kangas, Jared 1Dolgos, Kelley 1Randolph, Paris 2Kiefer, Kelley 2Thomas, Sean 2Dolin, Tyler 3Castle, Tim 3Gardner, Jawaad 3Baker, Benjamin 4Galdes, Nathan 4Hochstein, Molly 4Bradley, Andrea 5Thomas, Zane 5Burdock, Jacob 5Holden, Katrina 6Harris, Nicolas 6Pennington, Jacqueline 6Flowers, Doniesha 7Cane, Rachel 7Taylor, Chanelle 7Williams, Rhiana 8Dye, Carlynn 8Rooks, Jemar 8Jenkins, Crystal 9White, David 9Killmar, Jordan E 9van Well, Tyler 10Sanford, Ashley 10Wiley, Cody 10

Chem Catalyst• You have a pot of ice on the stove. You

heat up the water until it is boiling.– If you graphed the temperature of the water

over the time you are heating it, what do you think the graph will look like?

Time

Tem

p

http://molo.concord.org/database/activities/170.html

Chem Catalyst

When you have ice in a drink, the temperature will remain very close to 0 ºC. Only once all the ice has melted with the temperature start to rise.

• Why is this true? Think about heat transfer

Heating Curve of Water

ChemCatalyst1.) What phase or phases of matter are

present at points 1,2,3,4 & 5 on the heating curve of water?

Online Simulation

• http://jersey.uoregon.edu/vlab/Thermodynamics/index.html

Definition

• Thermal equilibrium is reached when two objects in contact with one another reach the same temperature.

You have two unknown substances. They each have a temperature of 65 degrees F. The first substances has a heat capacity of 0.12 cal/g*C. The second substance has a heat capacity of 0.63 cal/g*C.

Which substance will melt ice faster and WHY?

ChemCatalyst

Chem Catalyst

• Pretend you have a really cold drink in your hand. Which of the following substances would you want to wrap around it to keep it cold, and WHY???

-Aluminum foil, wood, or styrofoam? Justify your answer.

Specific Heat capacity of some metals

Metal Specific Heat Capacity

Initial Temp. Final Temp.

Aluminum 0.22 cal/g*C

Lead 0.031 cal/g*C

Zinc 0.093 cal/g*C

Severe second degree “burn” from salt/ice challenge

After effects of salt/ice challenge

Do conduction online demo

• Heat and temp molecular workbench demo – day two

Chem Catalyst

1.) Name three substances that will combust or burn.

2.) Name three substances that do not combust.

Demonstration

• Do metals combust? Let’s refresh our memories with magnesium.

Types of bonding

• Covalent =

• Ionic =

• Metallic =

• Elemental nonmetal =

Demonstrations

• Let’s make predictions if the following substances will combust:– Lamp Oil– Sodium chloride– Calcium carbonate– Iron

College Readiness Writing PromptIn some states, legislators have debated whether

teenagers should be required to maintain a “C” grade average in school before receiving a driver’s license. Some people think this would be a good policy because having passing grades shows that students are responsible enough to be good drivers. Other people think such a policy would not be appropriate because they see no relationship between grades in school and driving skills. In your opinion, should teenagers be required to maintain a “C” average in school before receiving a driver’s license?

Patterns of combustion

• Things that combust:– Most covalent molecules– Things with lots of C and H– Most metallic compounds

• Things that do not combust:– Ionic compounds– Water– Carbon dioxide– Oxygen gas

ChemCatalyst

• Which of the following substances are likely to combust? What is your reasoning?– C5H12, pentane

– CaBr2, calcium bromide

– Na, sodium

Chem Catalyst• Will the following substances combust or

not? Why?

- Bromine gas, Br2

- Pentane, C5H12

- Carbon Monoxide gas, CO

- Potassium, K- Magnesium nitrate, MgNO3

Question

• Burning wood for a campfire is a combustion reaction. Where does the energy come from that keeps the fire burning?

Notes

• Bond breaking:

requires energy. It takes energy to break the bonds that hold molecules together.

• Bond making:

releases energy. Forming new bonds to create new products actually releases energy.

“Make it or Break It”

Use the molecular model kits to have students build molecules necessary for the combustion of methane.

ChemCatalyst

It takes 860 kJ/mol of energy to break the bonds in the reaction of hydrogen gas and oxygen. 1050 kJ/mol of energy is released from forming the product, water.

1.) What is the net energy exchange? (or heat of reaction)

2.) Is this reaction endo or exothermic? How do you know?

Making Sense

• Reactions transfer heat.

• If the thermometer measured an increase in temperature, which direction was heat being transferred?

Reaction

Making Sense

• If the thermometer measured a decrease in temperature, which direction was heat being transferred?

Reaction

Making Sense

• When heat is transferred from the surroundings to the system (into the reaction), the reaction is called endothermic.

Reaction

Making Sense

• When heat is transferred from the system to the surroundings (exiting the reaction), the reaction is called exothermic.

Reaction

Chem Catalyst

• You have water at 43ºC. You dissolve ammonium acetate, NH4C2H4O2, in the water and find the temperature decreases to 24ºC.

1.) What is ∆T? Is it positive or negative?2.) Is the process exothermic or

endothermic?3.) Is energy transferring from the solution

to the environment or from the environment to the solution?

Chem CatalystGRAB A CALCULATOR

The specific heat of stainless steel is 0.12 cal/g*ºC. If you used 900 calories to heat 2.3 g of stainless steel, how much did you raise the temperature?

Rearranged equation:q ∆T

m * C

Re-worked probs for Fire 1

• Point of View: Draw pictures of heat transfer, Making sense

• Heat vs. Temp Summary: 1, 2, 3, 4, 5, 6

• The heat is on: Part 2, #2, 3, Making Sense

• Where’s the heat: Draw a heating curve graph, #1, #3

• You’re Fired: #1-5

• Hot and Cold: #2, #3, #7a,b,c

Chem Catalyst• The following table shows the balanced

chemical equations for four combustion reactions. List three patterns that you notice.

Substance Combustion reaction

methane CH4 + 2O2 --> CO2 + 2H2O

ethanol C2H6O + 3O2 --> 2CO2 + 3H2O

glucose C6H12O6 + 6O2 --> 6CO2 + 6H2O

magnesium 2Mg + O2 --> 2MgO

Making Sense

• Write the equation for the combustion of the following substances:

Sodium, Na

Propanol, C3H8O

Check-in

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

• K

• C2H6O

• CH4O

Chem Catalyst• 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?

(octane) ___C8H18 + ___O2 --> ___CO2 + ___H2O

(methanol) ___CH4O + ___O2 --> ___CO2 + ___H2O

(nitromethane) ___CH3NO2 + ___O2 ---> ___CO2 + ___H2O + ___NO2

Chem Catalyst1.) Below is the heating curve of water. What phase (or

phases) of matter are present at points 1, 2, 3, 4, and 5?

2.) Why does the temp stay constant at stages 2 and 4?

Quick Calculation• Octane (C8H18) generates 1300 kilocalories per mole

burned.

• How many calories are in 1 kilocalorie?

• What is the molar mass of octane?

• What’s another way of writing the molar mass?

• How many kilocalories are produced for every gram of octane?

Making Sense

• Metric units of energy (what scientists normally use) = Joule

• 1 calorie (cal) = 4.184 Joules (J)

• 1000 calories = 1 kcal

• 1000 J = 1 kJ

• 1 kilocalorie (kcal) = 4.184 kilojoules (kJ)

Practice Problems - Use Factor Labeling

• Convert 15 calories to Joules.

• Convert 2500 calories to kilojoules.

Chem Catalyst

• Previously, we learned that endothermic reactions absorb heat energy. These reactions feel colder as the reaction proceeds.

1.) If energy is absorbed by the reaction, why does it feel colder? Where does the energy go?

Chem Catalyst

• Humans generate energy from burning fuels, such as coal, oil, natural gas, and hydrogen. For example, the combustion of coal can be written asC (s) + O2 (g) --> CO2 (g)

• Do you think you can reverse the reaction to form coal, C(s), and oxygen, O2, from CO2? Explain your thinking.

Honors Chem:The rest of the year…

• Tuesday: Make sparklers

• Wednesday: Fire Starter

• Thursday: Study day for finals

• Friday: Optional 20 question MC quiz for Fire Investigation 2 (All-a-glow, Fuelish choices, No going back, Fire Starter)

• Monday: Study day, light sparklers

• Tuesday: Final Exam, 80 questions MC

Demos

• Demo 1 - Combustion of hydrogen

• Demo 2 - Decomposition of water

Energy Diagrams

2 H2 + O2

2 H2O

Reaction 1: Combustion of hydrogen

2H2 + O2 --> 2H2O

2 H2O

2 H2 + O2

Reaction 2: Decomposition of water

2H2O --> 2H2 + O2

-286 kJ/mol H2 +286 kJ/mol H2

Energy Diagrams

• Heat of reaction (rxn): The amount of energy gained or lost in a rxn. If the heat of rxn is negative, the rxn is exothermic. If the heat of rxn is positive, the rxn is endothermic.

Notes

• Law of conservation of energy: Energy is neither created nor destroyed.

Chem Catalyst

• Sketch an energy diagram for the combustion of carbon (coal) to form carbon dioxide. The heat of reaction is -394 kJ/mol.

• What energy is required to form coal from carbon dioxide?

Chem CatalystIn the previous lesson we showed you an empty energy diagram

for the combustion of hydrogen. This new energy diagram is more accurate.

1.) What is different about this diagram? 2.) Does more energy go into breaking the bonds, or is there more

energy released from making bonds?3.) Does this represent an endo or exothermic rxn?

-286 kJ/mol H2

2H2 + O2

2H2O

Energy Diagrams

Reactants

Products

Ea

Energy of Activation: The energy that is required to get a reaction started.

Making Sense

Reactants

Products

Ea

Bond energy: The energy required to break a bond. Bond breaking is endothermic (it takes energy to break a bond). Bond making is exothermic.

Check-in

-Which arrow represents the activation energy - heat going into the system?

-Which arrow represents the heat of reaction - net energy released by the reaction?

-For the reaction described by the energy diagram, is the energy required to break bonds greater than the energy released upon forming bonds?

-Is the reaction endothermic or exothermic?

Reactants

Products

c.b.

a.

Chem Catalyst - Review

• Propane (C3H8) burns in air to produce water and carbon dioxide. If 25.0 g of propane were burned, how many grams of water were produced?

• Write a balanced equation and set up a BCA table. This involves several steps, so make sure you don’t skip any.

Gas Law Problems• A gas in a closed, rigid container has a pressure of

1.5 atm at a temperature of 30ºC. If the temperature of the gas is raised to 250ºC, what is the new pressure?

• A gas in a syringe has a pressure of 700 mmHg and a volume of 45 mL. If the volume is decreased to 32 mL, what is the new pressure?

• A gas in a closed container has a pressure of 14 psi and has 3.5 moles of gas. If the amount of gas is increased to 4.6 moles, what will the new pressure be?

Heat Transfer Problem

• Which of the following takes more energy to do? Justify your answer with a calculation.

• Heating a 5.0 g piece of aluminum from 10ºC to 25ºC. The specific heat capacity for aluminum, CAl = 0.22 cal/gºC.

• Heating 5.0 g of water from 10ºC to 13ºC. The specific heat capacity for water, Cwater = 1.0 cal/gºC.

Video Demonstration

• http://www.youtube.com/watch?v=yTzcoyzPQE0

• Reaction between barium hydroxide and ammonium thiocyanate (basically the same reaction as what’s on your worksheet)

• Beginning Temp:• Ending Temp:

• Temp Difference = Tfinal - Tinitial =

Reaction of copper sulfate in water - demonstration

• Beginning Temp =

• Final Temp =

• Temp Difference = Tfinal - Tinitial =

Lab demonstration for today

Making Sense - Temp differences

Team Demo S1 S2 S3 S4 S5

1

2

3

4

5

6

7

8

Classify the reactions as endothermic or exothermic

• Combustion:

• Ba(OH)2*8H2O + 2NH4NO3:

• Dissolving CaCl2:

• Dissolving of NH4Cl:

• Dissolving of CuSO4:

• NaOH + HCl:

Check-in

• You have water at 25ºC. You dissolve ammonium acetate, NH4C2H4O2, in the water and find the temperature decreases to 15ºC.– Is heat being transferred from the solution

to the environment or from he environment to the solution?

– Is the process exothermic or endothermic?

Test on Fire Inv. 1

Investigation 2

• All a Glow

• Fuelish Choices

• No going back

• Fire Starter

• Sparklers