1. Heat & Thermodynamics
Physics I

2. Mechanical Equivalent of Heat: 4.186 J = 1 calorie
Heat The transfer of energy result of different temperature.
Temperature The average KE of individual molecules
Thermal/Internal Energy Total energy of all molecules (PE + KE)
Mechanical Equivalent of Heat: J = 1 calorie

3. Which way does heat flow?
Draw arrows indicating direction of flow
40 C
20 C
80 C

4. Heat Transfer: Conduction
In conduction energy is passed from atom to atom. It is the most important type of heat transfer in solids.
Convection
In convection, energy is carried around by atoms or molecules - so it only happens in liquids and gases.
Radiation
In radiation, radiant energy (infra- red) is given off by a hot object and absorbed by another object. No medium is required.
Sun
Hot Rocks

5. Identify the type of heat transfer in each illustration.
Demonstration Video of Convection
Ice

6. You notice that when you step out of the shower, the tile floor feels cold, but the mat is "warm". Why?
Conceptual Physics (2002b)

7. Conduction
think!
You can place your hand into a hot pizza oven for several seconds without harm, whereas you’d never touch the metal inside surfaces for even a second. Why?
Answer:
Air is a poor conductor, so the rate of heat flow from the hot air to your relatively cool hand is low. But touching the metal parts is a different story. Metal conducts heat very well, and a lot of heat in a short time is conducted into your hand when thermal contact is made.

8. Reactions Endothermic – Absorbs Heat and feels cooler
If heat is added to a reaction it will feel cold to you
Exothermic – Releases Heat and feels hot

9. Converting Temperatures
Converting Celsius and Fahrenheit
Examples
Convert 20 C to F.
Convert 89 F to C.
Converting Celsius to Kelvin:

10. The specific heat capacity of a material is the quantity of heat required to raise the temperature of 1 gram by 1 degree.
Specific Heats (J/kgC):
Ice = 2090
Water = 4186
Steam =2010
Gold = 129
Copper = 385
Units:
Q = Joules (J)
c = J/kgC
T = Celcius
m = kg
STAAR Chart

11. Specific Heat and Calorimetry Sample Problems
1.How much heat is required to change 300 g of water from 5° C to 85° C? (specific heat of water = 4186 J/kg C)

12. Your Turn!
2. How much heat is required to change 193 g of ethanol (specific heat = 2460 J/kg°C) from 19° C to 35° C?

14. Thermal Energy and Expansion
If the ring is heated, what will happen to the center hole? Will it expand or contract?

15. Thermostats use bimetallic strips
The Bimetallic Strip
Why does it bend when heated?
Thermostats use bimetallic strips

16. Thermal Expansion
Linear Area Volume
Expansion Joints

17. Salt
Why do cooks add salt to water when they are going to boil pasta? Is it just for the flavor or is something else going on?

18. Salt
Why do cooks add salt to water when they are going to boil pasta? Is it just for the flavor or is something else going on?
Something else: ain't just for the flavor...It turns out that adding salt make the water boil hotter and thus the pasta cooks faster.

19. Heat Transfer - Phases
Heat (J)
Temp

20. Latent Heat of Vaporization
Latent Heat of Fusion
Solid to Liquid
Liquid to Solid
No Temperature Change
Latent Heat of Vaporization
Gas to Liquid
Liquid to Gas
No Temperature Change
Water:
Lf = 3.33x105 J/kg Lv = 2.26x106 J/Kg

21. Thermal Equilibrium – Equal Temperature

22. Thermal Equilibrium – Equal Temperature
300 ml

23. Calculate final temperature.
Silver has a specific heat of 236 J/kg. What will be the final temperature if a silver ring with a mass of 12.0 g and a temperature of 115oC is dropped into 32.0 g of water initially at 25oC. Assume that no heat is transferred to the container

24. The Latent heat of fusion of lead is 23,200 J/kg
The Latent heat of fusion of lead is 23,200 J/kg. How much energy is needed to melt 135 g of lead once you get it to its melting point of 870oC

25. Convert your grams to kilograms first!
A 29.5 g sample of methanol at K is mixed with 54.3 g of methanol at K. Calculate the final temperature of the mixture assuming no heat is lost to the containers and surroundings. The specific heat of methanol is 2530 J /kgK
Convert your grams to kilograms first!

26. Ideal Gas Law

27. PV= nRT Relationships V P P T V T
Inversely Directly Directly Proportional Proportional Proportional

28. Temperature & Pressure Relationship
At higher temperatures, molecules move faster (more KE), causing more collisions and more pressure.
Boiling Water with Ice – Video Demo

29. This law allows the creation and calibration of thermometers.
Zeroth Law of Thermodynamics
If two systems are in thermal equilibrium (same temperature) with a third system, then they are all in thermal equilibrium with each other. A B C
If A is in equilibrium with B and B is with C, then A is in equilibrium with C.
TA = TB = TC
This law allows the creation and calibration of thermometers.
Rod Nave, Hyperphysics

30. What is Internal Energy?
Internal energy is defined as the energy associated with the random, disordered motion of molecules; it refers to the invisible microscopic energy on the atomic and molecular scale.
Rod Nave

31. Entropy is the measure of the amount of disorder in a system.
Disorder increases; entropy increases.

32. Examples of Entropy

33. Bellringer:
You have 4 minutes to complete the following questions:
Thermal equilibrium occurs when two objects have the same temperature.
a. True b. False
During the phase change, the temperature
a. increases b. decreases c. remains the same.
3. What is the specific heat for a 1 kg substance that increases from 20 C to 50 C when 6000 J of heat is added?

34. What increases or decreases the internal energy?
a) Work done on or by a system (ex. Change in volume)
b) Heat added or removed from a system
Particles will be moving slower!
Decrease in internal energy
Increase in internal energy
Particles will be moving faster!
1st Law of Thermodynamics (Pre-AP)

35. Wikipremed. (n.d.)

36. Heat Engines
A heat engine is a system that performs the conversion of heat or thermal energy to mechanical work and expels the unused heat.
Examples:
steam engine, diesel engine, gasoline engine
Conservation of Energy!!

37. Heat Engines
Conceptual Physics (2002c)

38. Refrigerator/Heat Pump
Heat Pumps transfer heat from a cold to a hot region or backwards with respect to normal heat flow. To do so requires a work input.
Examples:
Heat pump, refrigerator, air conditioner

39. More Practice Problems
1. Hypothermia can occur if the body temperature drops to 35.0 C., although people have been known to survive much lower temperatures. On January 19, 1985, 2-year-old Michael Trode was found in the snow near his Milwaukee home with a body temperature of 16.0 C. If Michael's mass was 10.0 kg, how much heat did his body lose, assuming his normal body temperature was 37.0C? (specific heat = 4186 J/kg C)

40. 2. Gwyn's bowl is filled with 0
2. Gwyn's bowl is filled with kg of 60 C soup(mostly water) that she stirs with a 20.0 C silver spoon of mass kg. The spoon slips out of her hand and slides into the soup. What equilibrium temperature will be reached if the spoon is allowed to remain in the soup and no heat is lost to the outside air? (cspoon = 240. J/KgC) Assume the temperature of the bowl does not change.

41. Summary of Formulas:
Specific heat of water = 4186 J/kg C

42. Bellringer:
You have 4 minutes to complete the following questions:
Thermal equilibrium occurs when two objects have the same temperature.
a. True b. False
During the phase change, the temperature
a. increases b. decreases c. remains the same.
3. What is the specific heat for a 1 kg substance that increases from 20 C to 50 C when 6000 J of heat is added?
200 J/kg C

43. Bellringer:
You have 4 minutes to complete the following questions:
Entropy is increasing.
A. True B. False
Which strip bends when heated?
a. a lead strip b. a bimetallic strip c. an aluminum strip
3. Which substance conducts heat well?
a. wood b. glass c. metal d. plastic
4. The nuclear reaction in a nuclear power plant relies on a self-sustaining reaction otherwise known as a
a. chain reaction b. mobius loop reaction
c. ladder reaction d. stair-step reaction

44. Bellringer:
You have 4 minutes to complete the following questions:
Entropy is increasing.
A. True B. False
Which strip bends when heated?
a. a lead strip b. a bimetallic strip c. an aluminum strip
3. Which substance conducts heat well?
a. wood b. glass c. metal d. plastic
4. The nuclear reaction in a nuclear power plant relies on a self-sustaining reaction otherwise known as a
a. chain reaction b. mobius loop reaction
c. ladder reaction d. stair-step reaction

45. Bellringer:
You have 4 minutes to complete the following questions:
Which object contains more energy, 1 kg of lead or 1 kg of feathers?
A. Lead b. Feathers c. The same
Heat flows from cold to hot objects.
a. true b. false
3. The first law of thermodynamics is associated with
a. entropy change b. change in internal energy
c. change in KE d. Conduction of heat
No system can convert all energy to work.
a. True b. False

46. Bellringer:
You have 4 minutes to complete the following questions:
Which object contains more energy, 1 kg of lead or 1 kg of feathers?
A. Lead b. Feathers c. The same
Heat flows from cold to hot objects.
a. true b. false
3. The first law of thermodynamics is associated with
a. entropy change b. change in internal energy
c. change in KE d. Conduction of heat
No system can convert all energy to work.
a. True b. False

47. Credits
Conceptual Physics (2002a). Chapter 21. [image]. Prentice Hall.
Conceptual Physics (2002b). Chapter 22. [image]. Prentice Hall.
Conceptual Physics (2002c). Chapter 24 [image]. Prentice Hall.
Nave, R. (n.d.). Hyperphysics. Permission granted to use illustrations in Presentations.
Wikipremed. (n.d.) Wisebridge Learning Systems LLC. Wikipremed.com. John Wetzel, an author at wikipremed.com. Retreived on March 20, 2012.