1. 講者： 許永昌 老師 1

2. Contents Molecular Speeds and Collisions Pressure Temperature Thermal energy and Specific heat Thermal interaction and Heat Irreversible Processes & the 2 nd Law of thermodynamics. 2

3. The aim of this chapter Understand 3

4. Molecule Speeds ( 請預讀 P542) 4

5. Mean Free Path ( 請預讀 P543) The average speed of N 2 at 20 o C is about 500 m/s There must be some collisions happened. Reference: http://en.wikipedia.org/wiki/Diffusionhttp://en.wikipedia.org/wiki/Diffusion 5 ~10m ~0.1 s (of course not)

6. Mean Free Path (continue) More careful calculation (all molecules move) 6

7. Stop to Think What would happen in the room if the molecules of the gas were not moving? What would happen in an isolated room if the molecular collisions were not perfectly elastic? 7

8. Pressure in a Gas ( 請預讀 P544~P545) Objects: A wall whose normal is x direction. Molecules in the left hand side of this wall. Condition: perfectly elastic. 8 = ++ …+ …

9. The Root-Mean-Square Speed ( 請預讀 P545~P546) 9

10. Stop to Think & Exercise 10

11. Homework Student workbook: 18.1 18.5 18.6 11

12. Temperature ( 請預讀 P546~P548) Microscopic  avg Macroscopic T. Average translational kinetic energy:  avg  (½mv 2 ) avg. Kinetic Theory: PV=Nm(v x 2 ) avg. (v 2 ) avg =3(v x 2 ) avg. Ideal-gas Law: PV=Nk B T. We get 12

13. Temperature (continue) 13

14. Homework Student workbook: 18.7 18.10 14

15. Thermal Energy for monatomic Gases ( 請預讀 P549~P550) E th =K micro +U micro. For monatomic gases: E th =K micro. E th =N  avg = 3 / 2 Nk B T= 3 / 2 nRT. Owing to the 1 st Law of thermodynamics, We get C V = 3 / 2 R=12.5 J/mol K. Q: How about other systems? 15

16. The Equipartition Theorem ( 請預讀 P550~P551) 16 *Solid State Physics, Ashcroft/Mermin, P463

17. Specific Heat of diatomic molecules ( 請預讀 P552~P553) 17 Why? A: In quantum mechanics, 1. =nћ 2.Discrete energy levels for bounded states.

18. 不正規講法 18 0 T eff T T

19. Additional Remark ( 補充 ) For two particles system ~ m H =1.66*10 -27 kg, r~3.7*10 -11 m, ћ=1.05*10 -34 Js, k B =1.38*10 -23 J/K T eff ~180K (n=1) 19

20. Thermal Interactions and Heat ( 請預讀 P554~P555) 20 ThTh TcTc Heat System 1System 2 Probability

21. Exercise Conditions: System 1: 4.00 mol N 2 at T 1 =27 o C. System 2: 1.00 mol H 2 at T 2 =327 o C. 3 s.f. Find: Thermal energies T f =? Heat transfer=? 21

22. Homework Student Workbook: 18.12 18.14 18.15 22

23. Irreversible Processes and the 2 nd Law of Thermodynamics ( 請預讀 P556~P558) 23 Probability

24. Order, Disorder and Entropy ( 請預 讀 P558~P560) 24

25. Homework Student Workbook: 18.17 18.19 Student Textbook: 33 51 65 製作 Terms and Notation 的卡片，以方便自我練習。 25