1. St18:Thermal Energy/Temperature

2. Thermal Energy = the total energy of all the particles in a substance.
Unit for energy is the Joule

3. Thermal Energy To explain further:
-The warmer an object gets, the more thermal energy(also: kinetic energy) it has.
So what’s temperature?

5. Temperature vs. Thermal energy
Temperature is related to the average kinetic energy of the particles in a substance.

6. Kelvin- (absolute temperature scale)
Temperature Scales
Celsius Fahrenheit
0 ºC- freezing* 32ºF- freezing
100 ºC- boiling* 212ºF- boiling
(*in between are 100 equal parts called degrees)
Kelvin- (absolute temperature scale)
a. K = ºC + 273
Example:10 ºC = 283K
b. ºC = K – 273
Example: 10K = -263 ºC
Temperature has no upper limit!

7. Absolute Zero- Nature’s Lowest Possible Temperature
At this temperature molecules have lost all available kinetic energy
Can not get any colder

8. Recap: Thermal energy relationships
a. As temperature increases, so does thermal energy (because the kinetic energy of the particles increased).
b. At the same temperature, the thermal energy in a more massive substance is higher (because it is a total measure of energy).

9. 38 ºC (100ºF)
38ºC
(100 ºF)
Which has more Thermal energy?

10. 1st Law of thermodynamics
The gain or loss of thermal energy equals the amount of heat transferred

11. 2nd Law of thermodynamics
Heat never spontaneously flows from a cold substance to a hot substance
In other words….heat always goes from hot to cold!

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

13. 3rd law of thermodynamics
No system can reach absolute zero

14. St. 19: Specific Heat Capacity

15. Land heats up and cools down faster than water
6. Specific Heat
a. Some things heat up or cool down faster than others.
Land heats up and cools down faster than water

16. b. Specific heat is the amount of heat required to raise the temperature of 1 g of a material by one degree (C or K).
1) Cp water = 4.18 J / g ºC
2) Cp sand = .664 J / g ºC
This is why land heats up quickly during the day and cools quickly at night and why water takes longer.

17. Water’s specific heat-controls climate

19. How to calculate changes in thermal energy
H = m x T x C
H = change in thermal energy
m = mass of substance
T = change in temperature (Tf – Ti)
C = specific heat of substance

20. Practice Problems: Specific Heat
Aluminum has a specific heat of .902 J/g C° How much heat is lost when a piece of Aluminum with a mass of 23.9 g cools from a temp of 415 C° to a temp of 27 C°.

21. St. 20- Thermal Equilibrium

22. Thermal Expansion When an object is heated, it expands.
When object is cooled, it contracts.
This is known (to physics-types) as THERMAL EXPANSION.
as temperature increases molecules move faster (have a greater average translational KE) and move farther apart

23. Strange Thermal Expansion
Water contradicts this idea when it is heated from 0⁰C to 4⁰C – it actually CONTRACTS.
Water is the most dense at 4⁰C!
This is why fish can live in a lake that has ice on top – the water at the bottom is 4⁰C.
Remember,
0 ˚ C is 32 F So
4 ˚C is about 40 F

24. Thermal Equilibrium
When two objects in thermal contact reach the same temperature
No heat flows through between them!!

25. Ex: thermal equilibrium
Thermometers measure air temperatures. Thermometers work because matter expands when heated. Most thermometers are closed glass tubes containing liquids such as alcohol.

27. What would be the final temperature of the mixture of 50g of 20º water and 50g of 40º C water?

28. What would be the final temperature of 1 L of water at 20ºC and 2L at 40º C

29. Problem
A jar of tea is placed in sunlight until it reaches an equilibrium temperature of 32oC. In an attempt to cool the liquid to 0oC, which has a mass of 0.l80 kg, how much ice at 0oC is needed? Assume the specific heat capacity of the tea to be that of pure liquid water.

30. m ice = (.180kg)(4186 J/kgoC)(32oC) 3.33x105 J/kg = 7.2 x 10-2kg
m tea = 0.180kg
m ice = ? which is the mass of the water that has melted
cp tea = cp water = J/kgoC
H f = 3.33 x 105 J/kg and t final = 32oC
H lost = H gained tea loses and water gains only melting the ice
(mcDt)tea = (mHf)ice
m ice = (mcDt)tea
Hf ice
m ice = (.180kg)(4186 J/kgoC)(32oC)
3.33x105 J/kg
= 7.2 x 10-2kg

31. St. 21- Methods of Heat Transfer

32. Methods of Energy Transfer
1. Conduction- energy transfer from particle to particle that are in CONTACT
Conductors and insulators
Transfer of energy is slow
Works best in solids!

33. Examples of conduction
Ice cube melts
Metal spoon in boiling water

34. 2. Convection
Give energy to molecules then move the molecules based on density
Works best in liquids and gases

35. Why is it windy at the seaside?

36. Why does hot air rise and cold air sink?
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.

37. 3. Radiation Heat from the sun
Transmits without matter to carry energy
Ex: Fireplace

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

39. Absorb vs Emit Good absorbers are dark Ex: Pupil of eye
Good absorbers are good emitters
Good absorbers reflect very little
Good Emitter/good absorber
Poor emitter/ poor absorber
Dull black surface
Shiny silver surface
Rough surface
Smooth surface

40. 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.

41. 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.

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

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

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

45. Newton’s Law of cooling
Rate of cooling is proportional to the temperature difference

46. Greenhouse Effect
The warming effect whose cause is that short wavelengths enter the earth easier than long wavelengths exit the earth

47. St. 22- Phase Changes

48. A. Matter can exist in four phases: Solid, Liquid, Gas, and Plasma.
Phases of Matter
PLASMA
A. Matter can exist in four phases: Solid, Liquid, Gas, and Plasma.

49. 1. Vaporization-phase change from liquid to gas
A. 1st type of Vaporization:
evaporation- takes place at the surface
COOLING PROCESS
Higher energy leaves lower temp
Perspiration

50. 1. Vaporization B. 2nd Type of Vaporization :
Boiling- bubbles of vapor form due to pressure

51. 2. Sublimination Molecules jump directly from solid to gas
Dry ice and snow

52. 3. Condensation Change of a gas to liquid Warming process
Kinetic Energy is absorbed

53. Melting Point From solid to liquid
Add heat, molecules move faster, break bonds

54. Freezing point
From liquid to solid
Forming bonds

55. Between phase change, energy causes increase in temperature
Between phase change, energy causes increase in temperature! During phase change no increase in temp