Problem with Energy in Education

Two main goals: Describing energy in a system and how is heat measured.

Problem with Energy in Education
“Students cannot use energy to adequately describe or explain everyday phenomena.” Use the term energy to describe how a cup of hot coffee that cools as it sits on the table. Use the term energy to describe how a 150 g sample of ice at 0.0 ˚C melts and then warms 25.0˚C?

Tri-Fold Update

Initial Temperature (℃) Temperature Change (℃)
Day at the Beach Substance Initial Temperature (℃) Final Temperature (℃) Temperature Change (℃) Water Sand Lets write these as a sentence I will write the 1st one It takes J of energy to raise 1 g of water 1 degree Celsius

Energy Bar Charts Better know as: LOL Diagrams

Energy Bar Charts Better know as: Key Concept 15: Energy bar charts are how we can represent the role of energy when a system is changed.

Constructing an Energy Bar Chart
Consider this example: A cup of hot coffee cools as it sits on the table. 1. Determine what is in the system Everything else makes up the surroundings 3A #16 cup coffee

Decide whether Ech is involved
In this case, you start with coffee and end with coffee; particles are not rearranged to form new substances So, ignore Ech for now.

solids < liquids < gases
Assign values to Eph Key Concept 16: Assign values to Eph- Due to interactions between particles, the energy stored due to the arrangement of particles is ranked: solids < liquids < gases We choose to represent these phases by using: Solids = 1 bar Liquids = 2 bars Gases = 4 bars Number of bars for how much energy is needed to break. Later with energy constants, make the connection that we use 4 bars for gasses because Hv is 2260!

Assign values to Eph Key Concept 17: Example LOL for- A cup of hot coffee cools as it sits on the table. Use two Eph bars before and after because starts and ends as a liquid.

Choose bars for Eth depending on temperature
Use 4 bars for hot coffee and 2 bars for room temperature coffee Other values might also work; try to be consistent in your representations

Now show energy transfer
The final situation has 2 less bars of E than initial; 2 bars had to leave the system Still Key Concept 17!

Now, consider phase change
Key Concept 18: LOL Example- A tray of ice cubes (-8 ˚C) is placed on the counter and becomes water at room temperature What do we know about the situation? The system is the tray of ice cubes. The solid water turns to liquid water - no change in Ech The Eph increases (solidliquid) The Eth increases (temp rises) Now represent these changes in lol chart. 3A #

Initial & Final States Choice of bars for Eth arbitrary, but consistent. I generally use 2 bars for room temp and one bar for cold liquid, -8˚C should be < 1 bar.

Account for Energy Energy must flow into system via heating

With Your Shoulder Partner:
17. A can of cold soda warms as it is left on the counter.

21. Some water at room temp, is spilled on the counter and evaporates.

22. Water vapor in the room condenses on a cold surface.

23. A cup of hot coffee cools as it sits in the freezer (-5 ℃). 4 bar th 2 bar ph 2 bar th 1 bar ph 2 bar th and 1 bar ph leave syst

20. A pan of water (25˚C) is heated to boiling. Then some of the water is boiled away. Do separate energy bar charts for each stage of the process

End Tuesday

Two main goals: Describing energy in a system and how is heat measured.

Tri-Fold Update

Heat = Temp Mass This is where we’re at. We know we need to know how much and how the temperature changed, like with ice sculptures. Need to know how much and the temp changes We’re going to do some demos to make sure our equation works. + - ÷ ×

Boiling in a Balloon Lets write these as a sentence I will write the 1st one It takes J of energy to raise 1 g of water 1 degree Celsius

White Board Questions A B C
With your shoulder partner, pick one of these demos and write A, B, or C in the corner of your whiteboard. B C

White Board Questions Answer the following questions on your white board. During your demo did the system gain or lose energy? Did the objects gain or lose energy at the same rate? Which gained energy at a faster rate? What do you think accounts for the different rates of energy transfer (or heating)?

White Board Questions Imagine you are given 1g of aluminum and 1g of plastic at room temperature. 4. If you wanted to raise that 1g sample 1°C, which substance would require more energy? Draw the two. Make sure to show density! Press for that it depends on material, because same mass and same delta t

Heat = Temp __ Mass White Board Questions
Imagine you are given 1g of aluminum and 1g of plastic at room temperature. 4. If you wanted to raise that 1g sample 1°C, which substance would require more energy? Draw the two. Make sure to show density! Press for that it depends on material, because same mass and same delta t Takes less to heat sand, air, one of the two metals, and and aluminum. Heat = Temp __ Mass + - ÷ ×

Heat = Temp __ Mass __ Substance specific
White Board Questions Imagine you are given 1g of aluminum and 1g of plastic at room temperature. 4. If you wanted to raise that 1g sample 1°C, which substance would require more energy? Draw the two. Make sure to show density! Press for that it depends on material, because same mass and same delta t Takes less to heat sand, air, one of the two metals, and and aluminum. Push/press for specific substance heating rate Heat = Temp __ Mass __ Substance specific heating rate + - ÷ × + - ÷ ×

Every Substance has its own specific heating rate:
Plastic: J/gºC Aluminum: 0.87 J/gºC Don’t sentence yet!

Lets break down what plastic specific heat says:
Plastic: J/gºC Aluminum: 0.87 J/gºC Have write as sentence 1.131 joules of energy to heat 1g of plastic 1C We’ll get to energy untis later, so for now joues are energy units

Write each as a sentence.
Specific Heat Write each as a sentence. Plastic: J/gºC Aluminum: 0.87 J/gºC Have write as sentence 1.131 joules of energy to heat 1g of plastic 1C We’ll get to energy untis later, so for now joues are energy units

Tri-Fold Update

Specific Heat Or Heat = Temp____ Mass____ Specific Heat
Heat = Temp____ Mass____ Substances Specific Heating Rate Or Heat = Temp____ Mass____ Specific Heat + - ÷ × + - ÷ × Have write as sentence 1.131 joules of energy to heat 1g of plastic 1C + - ÷ × + - ÷ ×

Heat = Temp____ Mass____ Specific Heat
Exit Pass Why did we need to adapt our math equation for finding the heat of something? + - ÷ × + - ÷ × Heat = Temp____ Mass____ Specific Heat

End of Wednesday

Measuring Heat Or Heat = Temp____ Mass____ Specific Heat
Heat = Temp____ Mass____ Substances Specific Heating Rate Or Heat = Temp____ Mass____ Specific Heat + - ÷ × + - ÷ × Have write as sentence 1.131 joules of energy to heat 1g of plastic 1C + - ÷ × + - ÷ ×

Specific Heat Key Concept 19: The specific heat of any substance is the amount of heat required to raise one gram of that substance one degree Celsius. See the units! Some objects require more heat than others to raise their temperature.

Specific Heat Demos Water: 4.184 J/gºC Plastic: 1.131 J/gºC
Air: 1.02 J/gºC Plastic: J/gºC Aluminum: 0.87 J/gºC Water: J/gºC Sand: J/gºC Lets write these as a sentence I will write the 1st one It takes J of energy to raise 1 g of water 1 degree Celsius Reteach demos, we talked about demo 2, so do the rest make sense? Why did magic wand bend? Tie to metal expands and diff heating so more and less expansions.

Specific Heat: Gas Real World Example

Specific Heat: Liquid Water: J/gºC Ethanol: 2.46 J/gºC

Specific Heat Capacity
What substance, out of everything ever, has the highest specific heat? What substance is the hardest to heat up?

Why is the high specific heat of water important?
Specific Heat: Liquid Why is the high specific heat of water important? Show list! Water is the highest!

Aqueous solution = in water
Key Concept 20: The high specific heat of water is important because: At least 80% of the mass of living organisms is water and almost all chemical reactions of life take place in aqueous solution. Aqueous solution = in water Thus a high specific heat minimises fluctuations in temperature inside cells and it also means that sea temperature is quite constant making Earth inhabitable. Heat Capacity (Start 9:15) Pause, and remind them that hydrogen bonds are intermolecular forces. Speaking of tests, as Hank mentioned, yours is November 2nd!

Specific Heat The specific heat of water depends on the state of the water. Why?

Specific Heat Notice it’s listed for all 3 states.
Substance and phase specific! Table is wrong!

Specific Heat The specific heat of water depends on the state of the water. Why? Recall: Intermolecular Forces! This is why with lols we use 4 bars Not just substance, but the state of matter. All substances specific heat deps on phase bec. Of intermolec forces Specific heat of ice = 2.09 J/g·ºC Specific heat of water (liquid) = 4.18 J/g·ºC 1 cal/g·ºC Specific heat of steam = 2.03 J/g·ºC

Can we now determine are the units of Heat?
Update tri-fold

Can we now determine are the units of Energy?

Unit of Energy Key Concept 21: Two unit of energy:
Joule (J) or calorie (cal) 4.184 J = 1 cal (on periodic tables) 1kJ = 1000 J kcal =1000 cal 1 Calorie = 1000 calories Really Wordy. Reformat maybe with bullets or two different slide. Break up the ideas.

Conversion Practice 1 cal = ________ J 1 Cal= ________ cal
1 kJ = ________J 4.184 .001

1 kJ = ________J Convert 300J to calories 71.7cal

1 kJ = ________J Convert 300J to calories 0.3J Covert 300J to kJ

1 kJ = ________J Convert 300J to calories 0.0717Cal Covert 300J to kJ Convert 300 J to Calories

1 kJ = ________J Convert 300J to calories 7.1128J Covert 300J to kJ Convert 1.7 cal to joules Convert 300 J to Calories

Specific Heat Since the specific heat of any substance is the amount of heat required to raise one gram of that substance one degree Celsius (Key Concept 19), we can calculate the specific heat of objects by heating them and seeing how much heating is required to raise a gram of that substance 1℃. One way we do this, is through Calorimetry!

Key Concept 22: Calorimetry is the science of
measuring the heat in a system or the process of measuring the heat capacity of different substances, using water.

Energy of a Food: Calorimetry Demo
Can’t see how much energy is in the cheeto, but can burn it, use that energy go into water, and can calculate how much is in cheetho. the number is calculated by seeing how much it releases. Energy lost by cheeto is energy gained by water. That’s how they get the back. I started at one tem, got final tem, so need temp change. Already heat in water, so need how much added, so need change.

Energy of a Food: If we were to improve the way I measured the energy in the food, how could I do so? Closed system!

Types of Calorimeters Open System: can exchange both matter and energy with the surroundings (e.g. open reaction flask, rocket engine) Closed system! Closed System: can exchange only energy with the surroundings e.g. a sealed reaction flask Isolated System: can exchange neither energy nor matter with its surroundings (e.g. hydro flask)

Types of Calorimeters Bomb Calorimeter Closed system!

Heat J= ℃ ___ g ____ J/(1g x 1∘C)
Heat = Temp & Mass & Substance Specific Lets take it to units J= ℃ ___ g ____ J/(1g x 1∘C) How do we get joules by its self its multiplication You started off thinking heat and temp are the same thing Could I of just told you Now we know how it works + - ÷ × + - ÷ ×

Heat J= ℃ ___ g ____ J/(1g x 1∘C)
Heat = Temp & Mass & Substance Specific Lets take it to units J= ℃ ___ g ____ J/(1g x 1∘C) How do we get joules by its self its multiplication You started off thinking heat and temp are the same thing Could I of just told you Now we know how it works

Specific Heat q = cp × m × ΔT Key Concept 23: How to calculate heat:
Heat = ΔT (Mass)(Specific Heat) Back of periodic table! q = cp × m × ΔT q = energy absorbed or released (through heating) (J) c = specific heat of substance (J/g °C) m = mass of substance in grams (g) ΔT = change in temperature in Celsius (°C) (Final – Initial)

Prove It Quiz Tuesday at the beginning of class.
Practice Problems 3A and 3B. Practice Problem B is HARD!!!!!!!! As homework tonight 1-10.

Exit Pass How do we calculate the calories in food? (You must mention water in your answer!)

End of Thursday

Bell Work Write the specific heat for copper and steel in a complete sentence. (AKA TWO SENTENCES) Copper: J/gºC Steel: J/gºC Make this on a piece of paper

Specific Heat q = cp × m × ΔT Key Concept 23: How to calculate heat:
Heat = ΔT (Mass)(Specific Heat) Back of periodic table! q = cp × m × ΔT q = energy absorbed or released (through heating) (J) c = specific heat of substance (J/g °C) m = mass of substance in grams (g) ΔT = change in temperature in Celsius (°C) (Final – Initial)

Key Concept 24: Temperature Change Phase Change
Draw out together and make the connection why we have to use different equations. Will write out q=mct on the temp inc on the board. 1.99J/g℃ gas 2260J/g liquid + gas 4.184 J/g℃ liquid 334 J/g solid + liquid 2.1 J/g℃ solid We left with heat is change in heat, specific heating rate, cp, and mass. That’s what we’ve been using. But what about the pleateaus? We can still use q=mt specif heating rate! Can delete t because if you put in K, tf – ti then 1 so can toss out. I always just plug chugged, didn’t question why or care why diff cp and equ for diff problems. Now I know, I have the graph so I can see why the temp is gone! Temperature Change Phase Change

Key Concept 24: Temperature Change Phase Change Q = mCp ΔT Q = m × ΔHv
Draw out together and make the connection why we have to use different equations. Will write out q=mct on the temp inc on the board. We left with heat is change in heat, specific heating rate, cp, and mass. That’s what we’ve been using. But what about the pleateaus? We can still use q=mt specif heating rate! Can delete t because if you put in K, tf – ti then 1 so can toss out. I always just plug chugged, didn’t question why or care why diff cp and equ for diff problems. No I know, I have the graph so I can see why the temp is gone! Q = mCp ΔT Q = m × ΔHf Temperature Change Phase Change Q = mCp ΔT

Key Concept 24: Temperature Change Phase Change Q = m(1.99J/g℃)ΔT
1.99J/g℃ gas 2260J/g liquid + gas 4.184 J/g℃ liquid 334 J/g solid + liquid 2.1 J/g℃ solid Q = m(4.184J/g℃) ΔT Temperature Change Phase Change Q = m (334J/g) Q = m(2.1J/g℃)ΔT

How to Calculate Heat Q = m × Cp × ΔT OR Q = m × ΔHv Q = m × ΔHf
Back of periodic table!

Heat = ∆Temp x Mass x Specific Heating Rate
H2O Equations and constants: q = mcT (for problems involving changes in temperature) Specific heat of ice = 2.1 J/g·ºC Specific heat of water (liquid) = 4.18 J/g·ºC 1 cal/g·ºC Specific heat of steam = 1.99 J/g·ºC q = m·Hfus or q = m·Hvap (for problems involving phase changes) Heat of fusion (melting/freezing) of water = 334 J/g Heat of vaporization (evaporating / condensation) =2,260 J/g Heat = ∆Temp x Mass x Specific Heating Rate

Heat = ∆Temp x Mass x Specific Heating Rate
H2O Equations and constants: q = mcT (for problems involving changes in temperature) Specific heat of ice = 2.1 J/g·ºC Specific heat of water (liquid) = 4.18 J/g·ºC 1 cal/g·ºC Specific heat of steam = 1.99 J/g·ºC q = m·Hfus or q = m·Hvap (for problems involving phase changes) Heat of fusion (melting/freezing) of water = 334 J/g Heat of vaporization (evaporating / condensation) =2,260 J/g Heat = ∆Temp x Mass x Specific Heating Rate You’ll be given these!

Answer the following on the back of your practice problems:
What specific heat would you use when ice is melting? What specific heat do you use when water condenses? What specific heat do you use when liquid water changes temp? What specific do you use when solid water (ice) changes temp?

What specific heat would you use when ice is melting? What specific heat do you use when water condenses? What specific heat do you use when liquid water changes temp? What specific do you use when solid water (ice) changes temp? 334 J/g

What specific heat would you use when ice is melting? What specific heat do you use when water condenses? What specific heat do you use when liquid water changes temp? What specific do you use when solid water (ice) changes temp? 2260 J/g

What specific heat would you use when ice is melting? What specific heat do you use when water condenses? What specific heat do you use when liquid water changes temp? What specific do you use when solid water (ice) changes temp? 4.18 J/g°C or 1 cal/g°C

What specific heat would you use when ice is melting? What specific heat do you use when water condenses? What specific heat do you use when liquid water changes temp? What specific do you use when solid water (ice) changes temp? 2.1 J/g°C

Example If you had 3 grams sample of liquid water and wanted to raise it 2℃, how much energy would it take? Cp liquid water = J/gºC Answer 6cal or J

Example If you had 10 grams of copper and wanted to raise it 10 ℃, how much energy would that take? The specific heat of copper is J/g℃. Same energy one is positive and one is negative LOL neg is leaving THERE IS NOT NEGATIVE ENERGY EVER!!!! LOL pos is coming

Example If you had 10 grams of copper and wanted to raise it 10 ℃, how much energy would that take? The specific heat of copper is J/g℃. Same energy one is positive and one is negative LOL neg is leaving THERE IS NOT NEGATIVE ENERGY EVER!!!! LOL pos is coming What if I wanted to decrease the temperature of 10 gram sample of copper 10 ℃? How much energy would need to be removed?

Move into Shoulder Partners

Practice Problem 11 A cup of coffee (140 g) cools from 75˚C down to comfortable room temperature 20.0˚C. How much energy does it release to the surroundings? DISCUSS NEGATIVE NUMBER Have them fix #12! Typo!

Practice Problem 13 Calculate the number of calories absorbed by the water, based on the information below. Mass of empty beaker: 300g Mass of beaker with H2O: 465g Temperature of water before reaction: 27.0˚C Temperature of water after reaction: ˚C

Practice Problem 15 Suppose that, during the Icy Hot lab, 65 kJ of energy was transferred to 450 g of water at 20 ˚C. What would have been the final temperature of the water?

Exit Pass What is the formula for heat? What are the units associated with each variable? ____ = ____ x ____ x ____ q = Cp= m = ΔT =

End Friday

How much heat is needed to raise 20g of solid water from -27℃ to -7℃?
Example Problem How much heat is needed to raise 20g of solid water from -27℃ to -7℃? 840J

Bell Work What equations would you use for heat at A, B, and C on the heating curve below? Include the specific heats. Use Key Concept 27! Make this on a piece of paper C B A Three equations!

Practice Problem 17 Suppose a bag full of ice (450 g) at 0.0 ˚C sits on the counter and begins to melt to liquid water. I do

Now try 18 with your shoulder partner
NOTE! Add in that we’re assuming the water is at 100℃ You do

A 150 g sample of ice at 0.0 ˚C melts and then warms 25.0˚C?
Practice Problem 19 A 150 g sample of ice at 0.0 ˚C melts and then warms 25.0˚C? I do

NOTE! Add in that we’re assuming the water is at 100℃ You do

Practice Problem 21 A 12oz can of soft drink (assume m = 340 g) at 25˚C is placed in a freezer where the temperature is – 12 ˚C. How much energy must be removed from the soft drink for it to reach this temperature?

NOTE! Add in that we’re assuming the water is at 100℃

Problem with Energy in Education

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