2. Chapter 10 Heat

3. Thermal Equilibrium Bring two objects into thermal contact. –They can exchange energy. When the flow of energy stops, the objects are in thermal equilibrium.

4. Temperature The quantity that tells how hot or cold something is compared to the standard. Measure of average KE of particles Increase temp……matter expands decrease temp….matter shrinks

5. Temperature A method of assigning numbers to objects that tells us about their thermal equilibrium. –If the two objects are in thermal equilibrium, they are assigned the same numbers. –If not, energy flows from the one with the higher temperature to the one with the lower temperature.

6. Temperature Measure of the average KE of any substance. Thermal energy is proportional to the amount of matter, temp. is not.

7. Temperature Newton proposed a method in 1701 –Used an alcohol-in-glass thermometer –Mixture of ice and water ---- 0 –Human body ----------------- 12 –Mark off 12 equal divisions 0 12

8. Thermometer Device used to measure temp. Celsius, Kelvin and Fahrenheit

9. Temperature International scale…..Celsius 0 o C…………..water freezes 100 o C…………water boils United States……..Fahrenheit Scale Scientific research is the SI scale…..Kelvin

10. Temperature Gabriel Fahrenheit suggested zero correspond to mixture of ice and salt –Was lowest lab temperature –Avoided use of negative temperatures –Each of 12 degrees divided into 8 –Human body -- 96 0 96

11. Fahrenheit Temperature Neither of fixed points was reproducible –fp of pure water at standard atmospheric pressure = 32 –bp of pure water at standard atmospheric pressure = 212 Best overall agreement Body temperature = 98.6 o F 32 212 98.6

12. Celsius Temperature Fixed points assigned new values –0 o C -- freezing point –100 o C -- boiling point Will leave conversions for you to learn. 0 100 37

13. Kelvin Temperature All gas thermometers give a lowest temperature of  273.15 o C Choose this as the zero point. Use better fixed point  triple point of water  0.01 o C 0 K  absolute zero 273 373 310

14. Thermal Energy The total energy of particles in a material. KE and PE

15. Thermal Energy Units calorie (cal) - amount of heat required to raise the temperature of 1 g of water by 1 c. Calorie (food) = kilocalorie British thermal unit (Btu) - amount of heat required to raise the temperature of 1 lb of water by 1 o F. joule - same as in mechanics

16. Mechanical Equivalent of Heat Can increase the internal energy of a body by –adding thermal energy –doing work on the body Therefore, there must be an equivalence –1 cal = 4.186 J

17. Example A drop of water falls a distance of 100 m. How much will its temperature rise when it hits the bottom? Any assumptions?

19. Heat The energy transfer from one object to another because of a temperature difference between them Matter doesn’t contain heat…….. Contains energy…..Heat is energy in transit

20. Heat Thermal Contact….. ……..When heat flows from one object to another that it contacts Energy that flows from areas that are higher in temp to areas that are lower in temp There is NO such thing as cold

21. Measurement of Heat To quantify heat, we must specify the mass and the kind of substance affected calorie….The amount of heat required to raise the temperature of 1 gram of water by 1 o C Calorie………….1000 calories food

22. Specific Heat (c) The amount of heat required to raise the temp of 1mass unit of a substance by 1 temp. unit. Thermal inertia…… signifies the resistance of a substance to change in temp.

23. Computing thermal expansion Q = mC  T Q = heat gained or lost (J) m = mass (kg)  T = change in temp (K) C = specific heat (J/kg K)

25. Calorimeter Device used to measure changes in thermal energy it is a closed system to measure energy transfer

28. Heat of Fusion H f Amount of energy needed to melt one kg of a substance ice= 3.34 x 10 5 J/kg ice= 80 cal

29. Melting Point Temp at which a substance changes from a solid to a liquid same temp. as freezing point

30. Heat of Vaporization H v Amount of energy needed to vaporize a kg of liquid water = 2.26 x 10 6 J/kg water= 540 cal

31. Boiling Point Temp at which a substance changes from a liquid to a gas Same as temp for condensation to occur

32. Q=mH f or Q=mH v Q….heat required to melt a solid or vaporize a liquid m….mass

33. Thermal Energy The total energy of particles in a material. KE and PE

34. Thermal Energy Transfer Occurs in 3 ways… CONDUCTION CONVECTION RADIATION

35. Conduction Transfer of energy from molecule to molecule Most common in solids KE is transferred when particles collide MUST have direct contact

36. Conductors Materials that conduct heat well Metals……….Silver

37. Insulators A material that is a poor conductor Delays the transfer of heat Examples… wood, wool, straw, paper Poor conductor is a good insulator

38. Convection Movement of all fluids (gas or liquid) Caused by substances having diff. Densities at diff. temps. Movement occurs in currents Example…….water, air

40. Radiation Thermal energy transferred through space in the form of electromagnetic waves. Examples ….Solar energy,

41. Example What does this mean? Convert to grams because we know what one cal does to one gram.

42. Specific Heat Heat Capacity = amount of heat required to raise T by 1 o C –Not very useful because it is not a property of the material Specific Heat = Heat Capacity per unit mass –Intrinsic property of the material

43. Calorimetry Conservation of Energy Assume that no energy is lost to the surroundings Heat Gained = Heat Lost

44. Calorimetry Assume that we drop a lump of gold (m = 20 g) at 100 o C into 50 g of water at 20 o C. What is the final equilibrium temperature? Heat lost = m g c g (T g  T e ) Heat gained = m w c w (T e  T w ) –note that both are positive –equate and solve for T e

45. Calorimetry Do we need to use Kelvin temperatures?

46. Calorimetry Let’s check to see if this is correct. It checks! The small difference is due to roundoff.

47. Latent Heat It requires heat to change the phase of a substance. Latent Heat is an intrinsic property –per unit mass Heat of fusion of water = 80 cal/g Heat of vaporization of water = 540 cal/g Q = mL

48. Latent Heat How much heat released in converting 1 g of steam at 120 o C to ice at  30 o C?

49. Cool steam, condense, cool water

50. Freeze and cool ice

51. Example A glass contains 120 g of ice at 0 o C. What is the equilibrium temperature if you add 400 g of water at 20 o C? Heat gained = heat lost

52. Example What ?!? Check for mistakes. –There are no mistakes. We made the assumption that all of the ice melted. Actually only 100 g melted!