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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:

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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.