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Thursday February 21, 2013Chapter 17: Thermochemistry
1. Calorimeter
2. Enthalpy
3. Heat capacity
4. Heat of combustion
5. Heat of reaction
6. Law of conservation
of energy
7. Molar heat of
condensation
8. Molar heat of fusion
9. Molar heat of solidification
10. Molar heat of solution
11. Specific heat
12. Standard heat of formation
13. Surroundings
14. System
15. Thermochemistry
BRING TEXTBOOK TOMORROW TOO!
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Wednesday February 18, 2015• Intro to
Thermodynamics
• Q Equation
EQ: How is specific heat related to conductivity?
ANNOUNCEMENTS:
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THERMOCHEMISTRY
The study of the changes in heat in chemical reactions
and physical processes.
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Heat EnergyHeat EnergyHeat EnergyHeat Energy
HEATHEAT is the form of energy that is the form of energy that flows between 2 objects flows between 2 objects because of their difference in because of their difference in temperature.temperature.
Other forms of energy —Other forms of energy —
• lightlight
• electricalelectrical
• kinetic and potentialkinetic and potential
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Heat TransferHeat TransferHeat TransferHeat Transfer
Heat transfers until thermal
equilibrium is established.
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Heat TransferHeat TransferNo Change in StateNo Change in State
Heat = (mass)(specific heat)(change in temperature)
Q = mcTQ: heat (joules)m: mass (grams)c: specific heat (J/goC or J/gK)T: change in temperature (oC or K)
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Specific Heat
The amount of heat required to raise the temperature of 1 gram (or 1 kg) of a substance by 1 K (or oC)
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Specific Heat
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Specific Heat
Is specific heat capacity related
to heat conductivity?
Iron
Wood
Air
Aluminum
Water
CONDUCT
OR?
INSULATOR?
https://www.youtube.com/watch?v=-wj2Oh50wsA
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A 15.75-g piece of iron is heated and as a result its temperature changes from 25°C to 175°C. Calculate the amount of heat absorbed by the iron.
Practice Problem #1
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Practice Problem #2
How much energy would be absorbed by 550 g of silver that is heated from 24oC to 45oC? (The specific heat of silver is 235 J/kgK)
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Practice #3
25.0 g of mercury is heated from 25°C to 155°C, and absorbs 455 joules of heat in the process. Calculate the specific heat capacity of mercury.
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Thursday February 19, 2015• Energy In a Cheeto
LabEQ: How much energy is stored in a cheeto? How are food calories related to heat energy?
ANNOUNCEMENTS:
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Heat TransferHeat TransferNo Change in StateNo Change in State
Heat = (mass)(specific heat)(change in temperature)
Q = mcTQ: heat (joules)m: mass (grams)c: specific heat (J/goC or J/gK)T: change in temperature (oC or K)
16Which has more Calories? Crunchy or Puffy Cheetos
All human activity requires “burning” food for energy. How much energy is released when food burns in the body? How is the caloric content of food determined? Lets investigate the caloric content of a popular snack food, Cheetos.
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Lab Setup
Safety Precautions
•Wear Goggles
•Tie back loose hair and sleeves
•No phone cords or headphones in lab
•No eating
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Ticket Out the Door
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Hint for #7
1 gram of water has a volume of 1 mL.
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Specific Heat Practice WSPart 2
1)0.46 J/gC or 460 J/kgC
2)0.14 J/gC or 140 J/kgC
3)32oC
4)0.131 J/gC or 131 J/kgC
5)1540 g
6)7600 J
7)14000 J
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HOMEWORK
•Complete the back
•Due tomorrow
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Friday March 14, 2014
Define specific heat.
The amount of energy required to raise 1 kg of a substance by 1 Kelvin.
Put your vocabulary in the tray at this
time!
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Specific Heat
The amount of heat required to raise the temperature of 1 gram (or 1 kg) of a substance by 1 K (or oC)
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All are units of heat energy.
1 calorie = 4.184 Joules– Specific heat of water in calories:
1.00 cal/gC
1 food Calorie = 1000 calories
Lab Setup:
•Use about 20 mL of water
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Please sit according to your lab station from Friday.
Stations 1 and 2 Stations 5 and 6
Stations 3 and 4
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Monday March 17, 2014
Warmup Question:
How are the “joule”, “calorie”, and “Calorie” related?
All are units of heat energy.
•1 calorie = 4.184 Joules– Specific heat of water in calories: 1.00 cal/gC
•1 food Calorie = 1000 calories
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Lab Calculations
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Today
• Exchange data with the other group.
• Use your data to make to make the calculations on the back.
• Turn in.
• Work on Heat Calculations WS
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Tuesday March 18, 2014
How much energy would be absorbed by 550 g of silver that is heated from 24oC to 45oC? (The specific heat of silver is 235 J/kgK)
Cheeto lab due at this time!!!
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Heat of Fusion&
Heat of Vaporization
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Wednesday February 25, 2015• Last Call:
–Cheeto Lab
–Heat Calculations WS
EQ: How much energy is stored in a cheeto? How are food calories related to heat energy?
ANNOUNCEMENTS:
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Thursday February 26, 2015
• Review phase change
• Heat of Fusion/Heat of Vaporization
EQ: What is difference between heat of fusion and heat of vaporization?
ANNOUNCEMENTS:
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solid liquid gas
PHASE CHANGE
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PHASE CHANGES
Melting
Solid to liquid
Energy absorbed
Freezing
liquid to solid
Energy released
Evaporation or Vaporization
Liquid to gas
Energy absorbed
Condensation
Gas to liquid
Energy released
Sublimation
Solid to gas
Deposition
gas to solid
http://www.youtube.com/watch?v=Hsu3JoXN-qU
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A,C,E: temperature changes; phase is constant
B,D: temperature is constant; phase changes
43Heat Transfer with Change of StateHeat Transfer with Change of StateSolid Liquid
Heat Transfer with Change of StateHeat Transfer with Change of StateSolid Liquid
Heat Transferred = (heat of fusion)(mass)
Q = (Hfus)(m)
Example: Example: Ice + Ice + 334 J/g (heat of fusion) 334 J/g (heat of fusion) -----> Liquid water-----> Liquid water
44Heat Transfer with Change of StateHeat Transfer with Change of StateLiquid Gas
Heat Transfer with Change of StateHeat Transfer with Change of StateLiquid Gas
Heat Transferred = (heat of vaporization)(mass)
Q = (Hvap)(m)
Example: Example: Water + Water + 2260 J/g (heat of vaporization) 2260 J/g (heat of vaporization) -----> Steam-----> Steam
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Which Q equation??
No Phase Change Phase change
Q = mcT solid/liquid: Q = (Hfus)(m)
liquid/gas: Q = (Hvap)(m)For water:
c = 4.18 J/gCHfus = 334 J/gHvap = 2260 J/g
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Friday February 26, 2015
• Kahoot: Which Q is it?
• Go over Parts 1 and 2
• Complete Part 3
EQ: What is difference between heat of fusion and heat of vaporization?
ANNOUNCEMENTS:
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Friday February 26, 2015
• Kahoot: Which Q is it?
• Go over Parts 1 and 2
• Complete Part 3
EQ: What is difference between heat of fusion and heat of vaporization?
ANNOUNCEMENTS:
50
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Work Session
Complete Heat Calculations WS. Check your answers with the key.
Hint: Be sure all of your units are in sync before you solve!
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Q=mcT
Q=mcT
Q=mcT
Q=Hfus(m)
Q=Hvap(m)
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Thursday March 20, 2014
A student uses the Q=mcT equation to figure out how much heat is gained by a piece of ice as it melts into liquid. Why is this incorrect?
The equation Q=mcT cannot be used for a substance undergoing a phase change, only while it is in one specific phase because temperature does not change in a phase change.
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Which Q equation??
No Phase Change Phase change
Q = mcT solid/liquid: Q = (Hfus)(m)
liquid/gas: Q = (Hvap)(m)
For water: c = 4.186 J/gC; Hfus = 334 J/g; Hvap = 2260 J/g
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Tuesday March 3, 2015
• Calculating Total Q
• Quiz
• Total Q partner activity
EQ: What is difference between heat of fusion and heat of vaporization?
ANNOUNCEMENTS:
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Total Heat Calculations
How much heat is required to raise 250.0 g of ice at a temperature of -15oC to room temperature of 21.0oC?
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Q=mcT
Q=mcT
Q=mcT
Q=Hfus(m)
Q=Hvap(m)
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HEAT EQUATIONS
Q = mcT
Q = (Hfus)(m)
Q = (Hvap)(m)
For water: c = 4.186 J/gC; Hfus = 334 J/g; Hvap = 2260 J/g
For ice: c = 2.06 J/g; For steam (gas): c = 2.02 J/g
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TOTAL Q ASSIGNMENT
With your partner:
•Draw a sketch of the phase change graph and label the START and STOP points for your problems.
•List the equations you would use to solve each step the problem.
•Solve the heat for each step.
•Find the total Q.
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