1. Heat and Temperature: Temperature Energy Transfer Using Heat
Chapter 14
Heat and Temperature:
Temperature
Energy Transfer
Using Heat

2. TN Standards
CLE – Examine the applications and effects of heat energy
CLE – Investigate the Law of Conservation of Energy
CLE.3202.TE.3 – Explain the relationship between the properties of a material and the use of the material in the application of a technology

3. TN Standards
SPI – Relate temperature changes with the changes of kinetic energy and the flow of heat energy

4. Bellwork What is temperature?
Average kinetic energy of particles in a material

5. Section 1 - Temperature Key Questions:
1] What does temperature have to do with energy?
2] What three temperature scales are commonly used?
3] What makes things feel hot or cold?

6. Temperature and Energy
Kinetic theory of matter
Matter is made of small particles always moving
Higher temperature, more motion
Large particles move slower
The temperature of a substance is proportional to the average kinetic energy of the substance’s particles
All particles have kinetic energy ( atomic )

7. Measuring Temperature
As materials are heated, they expand
Thermometers rely on expansion of liquids
Mercury or Alcohol
Thermostats rely on expansion of metals

8. Temperature Scales
Units: Fahrenheit ( English ) and Celsius ( metric )
Fahrenheit is English
Celsius/Kelvin is metric
Kelvin is an absolute scale
Absolute zero at oC

9. Temperature Scales - Converting
Celsius  Fahrenheit:
TF = 1.8*TC
Fahrenheit  Celsius:
TC = ( TF – 32.0 ) / 1.8

10. Temperature Scales - Converting
Celsius  Kelvin:
TK = TC
Kelvin  Celsius:
TC = TK

11. Temperature & Energy Transfer
When you feel “hot” or “cold” you are detecting a temperature difference
You are also feeling the affects of energy transfer
Temperature changes indicate an energy transfer – temperature difference between two objects is felt as heat
Heat is the energy transferred between objects of different temperature

12. Section 2 – Heat Transfer
Key Questions:
1] How does energy transfer happen?
2] What do conductors and insulators do?
3] What makes something a good conductor of heat?

13. Energy Transfer ( Heat Flow )
What is happening in each picture
Explain how heat is flowing ( ID how heat goes from one object to another )
What might be happening on the
atomic level?

14. Different Methods of Transfer

15. Different Methods of Transfer
Conduction occurs between objects in direct contact
Thermal Conduction–heat source is one object

16. Different Methods of Transfer
Convection results from the movement of warm fluids ( in contact with heat source )
Warm fluids rise
Cool when away from heat
Cool fluids fall
Convection current –
Path of warm/cool fluids

17. Different Methods of Transfer
Radiation does not require physical contact between objects
Energy transferred as
electromagnetic waves

18. Conductors & Insulators
A conductor is a material through which energy can be easily transferred as heat
An insulator is a material that transfers energy poorly
Heat energy is transferred through particle collisions

19. Conductors & Insulators
Heat energy is transferred through particle collisions
Gases – poor conductors
Why?
Denser materials usually are better conductors than less dense
Metals – very good conductors
Plastics – poor conductors

20. Bellwork – 11/21/14
When you melt ice, is heat going to be added to the water, or removed from it?
Add heat

21. Specific Heat Determines how easily energy can be transferred as heat
How much energy is needed to change the temperature of a substance by a certain amount

22. Specific Heat
Amount of energy needed to raise the temperature of 1 kg of substance by 1 K
1 degree change in C = 1 degree change K
Energy = specific heat x mass x temp change
Energy = cmΔT
c = energy /(mΔT)

23. Specific Heat
Temperature does not change when phases do; energy goes into phase change - not temperature adjustment
Latent heat ( melting ) & Heat of Fusion ( evap )
Gives amount of energy needed for phase change

24. Heat Flow Conceptual Practice
Scenarios – Explain what is happening:
1] You pick up a coffee cup and it is hot
2] You touch a glass of cold SCHAWEET tea
3] A breeze makes you shiver

25. Heat Flow Conceptual Practice
Which substance can you heat the quickest?
One with a large or small heat capacity?

26. Heat Flow Practice Problems #1
How much energy must be transferred as heat to 200 kg of water ( c = 4,186 J/kg/K ) in a bathtub to raise its temperature from 25 oC to 37 oC?:

27. Heat Example #2
The temperature of a substance increases by 7 K when 1850 J is added to a 5 kg quantity of the substance. What is the specific heat ( c )?

28. Heat Example #3
Temperature of 2.5 kg ethanol is 47 oC. What will the final temp be if 90,000 J of heat energy is added [ c = 2440 J/(kg*K) ].

29. Bellwork – 12/02/15
Is it possible to have heat flow FROM something that is COLD TOWARDS something that is HOT?

30. Section 3 – Using Heat Key Questions:
1] What happens to heat energy when it is transferred?
2] What do heat engines do?

31. Thermodynamics
1st Law – total energy used in any process is conserved, whether that energy is transferred as work, heat, or both.

32. Thermodynamics
2nd Law – energy transferred as heat ALWAYS moves from higher to lower temperature. Another way of saying “Energy is always conserved.”

33. Thermodynamics Entropy – randomness or disorder of a system
Thermo [3rd Law] tells us that total entropy of the universe is ALWAYS increasing ( natural tendency )

34. Usable vs. Unusable Energy
When energy is transformed, the amount of usable energy DECREASES
But overall, the total of usable and unusable energy REMAINS CONSTANT

35. What is a System?
A “system” is defined as the area, volume and/or group of objects being analyzed
Systems can be open or closed
Closed system – like a can of coke or soup that has not been opened
Open system – once you open that can of coke or soup

36. Heat Engines
Heat Engines – chemical energy is converted into mechanical energy by combustion

37. Heat Engines

38. Using Heat
Rubbing alcohol applied to the skin – what happens/what do you observe?
Why?

39. Using Heat
Rubbing alcohol applied to the skin – what happens/what do you observe?
Why?

40. Using Heat cooling/heating processes utilize this SWEATING!
Fluids—liquids & gases—are chosen that easily evaporate and condense
Evaporation – energy is absorbed by the fluid/sweat ( from surrounding air or body )
Condensation – energy is released by the fluid/moisture ( absorbed by air )