1. Heat
Transfer
YVHS Physical Sci

2. Instructions
Take a set of Cornell Notes for both Sections I & II of the presentation –
Taking a note about Pertinent information will cut down on notes
What is crucial information? What do I know already?
You should have 5 Review Questions and a paragraph summary

3. Heat Transfer Heat always moves from a warmer place to a cooler place.
Hot objects in a cooler room will cool to room temperature.
Cold objects in a warmer room will heat up to room temperature.

4. Heat Transfer Methods Heat transfers in three ways: Conduction
Convection
Radiation

5. Conduction
When you heat a metal strip at one end, the heat travels to the other end.
As you heat the metal, the particles vibrate, these vibrations make the adjacent particles vibrate, and so on and so on, the vibrations are passed along the metal and so is the heat. We call this?
Conduction

6. Metals are different
The outer e______ of metal atoms drift, and are free to move.
lectrons
When the metal is heated, this ‘sea of electrons’ gain k_____ energy and transfer it throughout the metal.
inetic
Insulators, such as w___ and p____, do not have this ‘sea of electrons’ which is why they do not conduct heat as well as metals.
ood
lastic

7. Why does metal feel colder than wood, if they are both at the same temperature?
Metal is a conductor, wood is an insulator. Metal conducts the heat away from your hands. Wood does not conduct the heat away from your hands as well as the metal, so the wood feels warmer than the metal.

8. The particles spread out and become less dense.
Convection
What happens to the particles in a liquid or a gas when you heat them?
The particles spread out and become less dense.
This effects fluid movement.
What is a fluid?
A liquid or gas.

9. Fluid movement
Cooler, more d____, fluids sink through w_____, less dense fluids.
ense
armer
In effect, warmer liquids and gases r___ up.
ise
Cooler liquids and gases s___.
ink

10. Water movement Cools at the surface Convection current Hot water rises
Cooler water sinks

11. Why is it windy at the seaside?

12. Where is the freezer compartment put in a fridge?
Cold air sinks
Where is the freezer compartment put in a fridge?
Freezer compartment
It is warmer at the bottom, so this warmer air rises and a convection current is set up.
It is put at the top, because cool air sinks, so it cools the food on the way down.

13. The third method of heat transfer
How does heat energy get from the Sun to the Earth?
There are no particles between the Sun and the Earth so it CANNOT travel by conduction or by convection.
RADIATION ?

14. Radiation Radiation travels in straight lines True/False
Radiation can travel through a vacuum
Radiation requires particles to travel
Radiation travels at the speed of light

15. Emission experiment
Four containers were filled with warm water. Which container would have the warmest water after ten minutes?
Shiny metal
Dull metal
Dull black
Shiny black
The __________ container would be the warmest after ten minutes because its shiny surface reflects heat _______ back into the container so less is lost. The ________ container would be the coolest because it is the best at _______ heat radiation.
shiny metal
radiation
dull black
emitting

16. Absorption experiment
Four containers were placed equidistant from a heater. Which container would have the warmest water after ten minutes?
Shiny metal
Dull metal
Dull black
Shiny black
The __________ container would be the warmest after ten minutes because its surface absorbs heat _______ the best. The _________ container would be the coolest because it is the poorest at __________ heat radiation.
dull black
radiation
shiny metal
absorbing

17. Convection questions Why does hot air rise and cold air sink?
Cool air is more dense than warm air, so the cool air ‘falls through’ the warm air.
Why are boilers placed beneath hot water tanks in people’s homes?
Hot water rises.
So when the boiler heats the water, and the hot water rises, the water tank is filled with hot water.

18. Radiation questions Why are houses painted white in hot countries?
White reflects heat radiation and keeps the house cooler.
Why are shiny foil blankets wrapped around marathon runners at the end of a race?
The shiny metal reflects the heat radiation from the runner back in, this stops the runner getting cold.

19. Section I Complete!
What was discussed? What are you unsure of? Advance the slide for a few brief assessment questions! ,
Continue to section II!

20. 1. Which of the following is not a method of heat transfer?
A. Radiation
B. Insulation
C. Conduction
D. Convection

21. 2. In which of the following are the particles closest together?
A. Solid
B. Liquid
C. Gas
D. Fluid

22. 3. How does heat energy reach the Earth from the Sun?
A. Radiation
B. Conduction
C. Convection
D. Insulation

23. 4. Which is the best surface for reflecting heat radiation?
A. Shiny white
B. Dull white
C. Shiny black
D. Dull black

24. 5. Which is the best surface for absorbing heat radiation?
A. Shiny white
B. Dull white
C. Shiny black
D. Dull black

25. Part II Calculating Thermal Energy
What is the Specific heat capacity of a material and how is it measured?
How is temperature related to the average kinetic energy of the particles in a substance?

26. SI unit for temp is Kelvin
K = C (10C = 283K)
C = K – 273 (10K = -263C)
Thermal Energy is the total of all the kinetic and potential energy of all the particles in a substance.

27. Thermal energy relationships
As temperature increases, so does thermal energy (because the kinetic energy of the particles increased).
If the temperature stays the same, the thermal energy in a more massive substance is higher (because it is a total measure of energy).

28. The flow of thermal energy from one object to another.
Cup gets cooler while hand gets warmer
Heat
The flow of thermal energy from one object to another.
Heat always flows from warmer to cooler objects.
Ice gets warmer while hand gets cooler

29. Specific Heat (c, sometimes s, but usually c)
Things heat up or cool down at different rates.
Land heats up and cools down faster than water, and aren’t we lucky for that!?

30. Specific heat is the amount of heat required to raise the temperature of 1 kg (but in Chem we use g) of a material by one degree (C or K, they’re the same size).
C water = 4184 J / kg C (“holds” its heat)
C sand = 664 J / kg C (less E to change)
This is why land heats up quickly during the day and cools quickly at night and why water takes longer.

31. Why does water have such a high specific heat?
water metal
Water molecules form strong bonds with each other water molecule; (including H-bonds!)so it takes more heat energy to break the bonds. Metals have weak bonds (remember the “sea of e-) and do not need as much energy to break them.

32. Q = Cp x m x T Q = change in thermal energy m = mass of substance
T = change in temperature (Tf – Ti)
Cp = specific heat of substance

33. Specific Heat Capacity
If 25.0 g of Al cool from 310 oC to 37 oC, how many joules of heat energy are lost by the Al?
heat gain/lose = q = (c)(mass)(∆T)
where ∆T = Tfinal - Tinitial
q = (0.897 J/g•K)(25.0 g)( )K
q = J
Notice that the negative sign on q signals heat “lost by” or transferred OUT of Al.

34. q transferred = (c)(mass)(∆T)
Heat can be Transferred even if there is No Change in State
q transferred = (c)(mass)(∆T)

35. Or… Heat Transfer can cause a Change of State
Changes of state involve energy (at constant T)
Ice J/g (heat of fusion) -----> Liquid water
Is there an equation? Of course!
q = (heat of fusion)(mass)

36. Heat Transfer and Changes of State
Liquid (l)  Vapor (g)
Requires energy (heat).
Why do you…
cool down after swimming ???
use water to put out a fire???

37. Remember this – The Heating/Cooling Curve for Water!
Evaporate water
Note that T is constant as a phase changes

38. q transferred = (c)(mass)(∆T)
So, let’s look at this equation again…
q = (heat of fusion)(mass)
(There’s also q = (heat of vaporization)(mass), by the way, for when we are talking about vaporization)
WHY DO I NEED THIS WHEN I HAVE
q transferred = (c)(mass)(∆T)
HUH???
Well, when a phase changes THERE IS NO change in temperature… but there is definitely a change in energy!

39. So… if I want the total heat to take ice and turn it to steam I need 3 steps…
1) To melt the ice I need to multiply the heat of fusion with the mass…q = (heat of fusion)(mass)

40. 2) Then, there is moving the temperature from 0 C to 100C… for this there is a change in temperature so we can use… q transferred = (c)(mass)(∆T)
3. Add!

41. What is the specific heat of a particular substance?
Task -
What is the specific heat of a particular substance?
Now, lucky for us, just like there are tables for specific heats (like the one in our outlines).
There are also tables for heats of fusion and heats of vaporization.
USING A SEARCH ENGINE, find a TABLE for specific heat of metals. What is the value for:
Iron Brass Copper Steel
( You’ll use these numbers in our lab).

42. Heat & Changes of State
What quantity of heat is required to melt 500. g of ice and heat the water to steam at 100 oC?
Heat of fusion of ice = 333 J/g
Specific heat of water = 4.2 J/g•K
Heat of vaporization = 2260 J/g
+2260 J/g
+333 J/g

43. And now… More! Heat & Changes of State
How much heat is required to melt 500. g of ice and heat the water to steam at 100 oC?
1. To melt ice
q = (500. g)(333 J/g) = x 105 J
2. To raise water from 0 oC to 100 oC
q = (500. g)(4.2 J/g•K)( )K = 2.1 x 105 J
3. To evaporate water at 100 oC
q = (500. g)(2260 J/g) = x 106 J
4. Total heat energy = 1.51 x 106 J = 1510 kJ