Heat and Thermal Energy

1. Heat and Thermal Energy

2. Temperature! • How hot or cold something is with respect to some standard

3. Try this! What do you notice? What's a standard?

4. A standard is a frame of reference that all agree on. If I asked you what temperature it was in the room, you’d all have different answers! But if I also gave you each a thermometer…

5. Thermometers • Thermometers work through the expansion and contraction of a liquid • Usually mercury or alcohol

7. In the U.S., we use Fahrenheit Most other countries use Celsius

8. Where did the Fahrenheit scale come from? • Daniel Fahrenheit got water to the lowest possible temperature. He called this 32. • He then set the upper limit of his scale to body temperature, or 96 degrees. Off a bit! • Next he tested the strength of his thermometer by placing it in boiling water. He found it to read 212, thus the upper limit Device was not so accurate! Silly Daniel!

9. Anders Celsius • Revised the Fahrenheit scale to be more logical. • Used freezing and boiling points of water for the zero and one hundred markers.

10. So, what does a thermometer do exactly? Measures temperature!

11. So, how does a thermometer work? thermal equilibrium and the expansion and contraction of liquids

12. Temperature is a measure of the AVERAGE KE of a substance • When atoms within a substance move faster, they have higher temperatures! This pencil was just sharpened

13. Why does it have to be the AVERAGE Kinetic Energy? Not all move at the same speed!

14. When you place a thermometer in a substance, heat flows from hot to cold until both have the same average KE’s The thermometer measures her temp. when heat flows from her head to the thermometer!

15. Thermometers actually read their own temperatures. Can you explain why?? Thermal Equilibrium! Energy flows back and forth until both substances have the same temp!

16. What makes something hot? Average KE! Click this for a video!

17. How do you heat something up? Add energy!

18. Make it move!

19. Ball at rest Ball after being bounced

20. What if I compressed the box? What happens to the temperature?

21. So what makes something cold? But how did they get cold? HotWater vapor molecules in warm air move faster.They are less likely to join together. ColdWhen air is cool, the molecules of watervapor move slowly.

22. To change the temperature…

23. WAIT!!!!!!!!!! • Not so fast! We forgot about KELVIN! Who? You know... Lord Kelvin!

24. Remember??

25. So what’s Zero on the Kelvin scale? Oh it can get a lot colder than this! • Zero on the Kelvin scale is equal to ABSOLUTE ZERO • That’s when all molecular motion ceases • Basically it’s the coldest anything can get!

26. Absolute Zero and temperature There is no theoretical limit on how hot something could get • Check out this webpage… • Is there an upper limit to the temperature scale?? • What do YOU think??

27. That's hot! That's cold!

28. How do you convert from one scale to another? www.fordhamprep.org/gcurran/sho/sho/review/rev29a.htm Try some of these with your partner!

29. How do you convert from one scale to another? C = (F – 32) 5/9 F = 1.8*C + 32 Pay attention to order of operations!!

30. How do you convert from one scale to another? C = K - 273 K = C + 273

31. So what’s thermal energy? • The sum of all the KE’s of the individual particles of a substance This one! Which box has more KE? This one!

32. Who’s got more thermal energy? Iceberg? Coffee?

33. OK then, what’s HEAT? • HEAT is when thermal energy is transferred from one object to another due to a temperature difference between them

34. Heat always moves from: Kinetic energy! HOT COLD WHY???

35. How does Heat Transfer?

36. Heat Units! Joules It takes 4.184 Joules to raise the temperature of 1 g of water by 1 oC

37. Heat Units! 1 calorie (cal) = amount of heat needed to raise the temperature of 1 g of water by 1 oC

38. The scientific "calorie" is spelled with a "c".One "calorie" = 4.184 Joules------------------------------------- The "dieter's" calorie is spelled with a "C".One "Calorie" = 1000 calories

39. Because of the confusion between Calorie and calorie, joules is commonly used for a unit of thermal energy.

40. Caloric values for some foods

41. 10 degrees C

42. U.S.A.

43. Specific Heat Capacity The specific heat of a substance is the quantity of energy needed to raise the temperature of 1g of the substance by 1°C.

44. The pans are of a similar type but different size. Each pan is filled with water. They are placed on heaters having the same power. In which pan would the water boil first?

45. This beaker contains 100 grams of water at 20°C.Let's see how the temperature changes as we add hot or cold water.

46. This beaker contains 100 grams of water at 20°C. Let's add 100 grams of water at 60°C to our 100 grams sample at 20°C.What temperature would you expect for the mixture?

47. What temperature would you expect for the mixture? 20, 30, 40, 50 ,60http://www.chem.uiuc.edu/webFunChem/GenChemTutorials.htm

48. A penny, marble and foil are at thesame temp. • Which one stays hot longer afterremoval from the bath?

49. Specific Heats of Various Substances

50. Which has the higher specific heat?