Heat and Thermodynamics Trefil & Hazen, The Sciences, Ch 4

1. Heat and ThermodynamicsTrefil & Hazen, The Sciences, Ch 4 Great Idea: Energy always goes from a more useful to a less useful form.

5. thermal energy that flows from object of higher temp. to object of lower temp. Measure of hotness, related to average kinetic energy per molecule in an object. Heat Temperature

6. 30's hot 20's nice 10's cold zero's ice

7. Celsius H2O bp = 100 H20 fp = 0 Fahrenheit H20 bp = 212 H20 fp = 32 Temperaturemeasure of the average kinetic energy of a substance

8. No upper limit to temperature apply heat to matter and change phases: solid liquid gas plasma Definite lower limit to temperature -273 C or –459 F “absolute zero” The point at which molecules lose all kinetic energy Absolute Zero (of temperature)

9. We’ve never achieved absolute zero, but we’ve come close! • Temp’s of approx. 0.000001K have been reached, but 0 K has never been reached

10. How do we know absolute zero exists? • Gases expand when heated, contract when cooled. • Gases at constant pressure, each 1oC drop in temp reduces volume by 1/273 • If a gas at 0oC were cooled to –273oC, it would contract down to a volume of zero

12. Specific Heat Capacity • A measure of the ability of a material to absorb heat energy • The quantity of heat required to raise the temp of 1 gram of that material by 1oC.

13. Specific Heats of Selected Substances • Substance Sp Ht (J/g-oC) • Water 4.18 • Aluminum 0.89 • Carbon 0.71 • Iron 0.45 • Mercury 0.14

14. Thermal Expansion • All phases of matter tend to expand when heated and contract when cooled. • Think of examples of the above phenomena to share with your students. • Discuss examples and engineering applications

15. Thermal Expansion

17. Melting Solid to Liquid Heat input increases molecular motion to the point that molecular connections break Freezing Liquid to Solid Energy dissipates and motion decreases “role-play” phase changes

18. Dry off outside shower Liquid water evaporates off of your body Water on your body is warmed and evaporates from liquid to vapor, gaining kinetic energy Mirror is “steamed up” Water vapor condenses on cooler glass Warm, moist air cools and condenses from vapor to water, losing kinetic energy Evaporation vs Condensation

19. Evaporation Sublimation

20. Figure 4-4 Convection. Heat is transferred by the bulk motion of the water.

21. Boiling • Evaporation that occurs beneath the surface of a liquid • “bubbles of vapor” • Depends on 2 factors: • Temperature • Pressure

22. At lower atmospheric pressure, boiling point is lowered Example: At Denver, water boils at 95oC instead of 100oC. Why? At higher pressure, boiling point is increased Example: common “pressure cooker” Why use one of these? Pressure and boiling…

23. Heat Transfer • Conduction • Convection • Radiation

24. conduction • The movement of heat by collision of vibrating atoms

25. convection • Transfer of heat by the physical motion of fluid. • (Dense cooler fluids descend and displace warmer rising fluids)

26. radiation Movement of heat by electromagnetic energy. (The only mechanism that does not require atoms to facilitate the transfer.)

27. Thermodynamics(Gr) “movement of heat” • Conduction = movement of heat through solids by atomic collisions • Convection = heat transfer in a gas or liquid via currents or bulk motion of the heated fluid • Radiation = transfer of heat through air or space as infrared waves

28. Thermodynamics • The study of the movement of heat • Also refers to the science of heat, energy, and work

29. Laws of Thermodynamics I Conservation of Energy: In an isolated system, the total amount of energy, including heat, is conserved. II Entropy or disorder Energy always goes from a more useful to a less useful form.

30. EnergyTransformation

31. The tendency toward disorder or entropy

32. Obstructions to the 2nd Law make life possible. • 2nd Law of Thermodynamics and evolution

33. In Trefil & Hazen’s text: • Please read about trophic levels and the first law of thermodynamics • Also see on the consequences of the second law of thermodynamics

34. Review Questions from ch 4 • discussion questions 1, 2, 4, 6-9 • problems 1 & 6, p. 90.