1. Physics 1220/1320 Thermodynamics & Electromagnetism Chapter 19 -20

2. Ideal Gas: Phase Diagram: Substance expanding on melting

3. Ideal Gas to real gas: Phase transitions Here: liquid/gas

5. Phase diagrams – 3-dim pVT system

7. Examples of quasi-static processes: isothermalconstant T isobaricconstant p isochoricconstant V adiabaticno heat flow

8. 1 st Law of Thermodynamics Conservation of energy:

9. State Functions

10. Graphical representation of quasi-static processes

14. State Functions Ideal gas - Isothermal processes

16.  = C p /C v = (5/2R)/(3/2R)=5/3

17. TV  -1 = const.

19. Second Law of Thermodynamics: gives direction to processes No system can undergo a process where heat is absorbed and convert the heat into work with the system ending in the state where it began: No perpetuum mobile.

20. b/c heat cannot flow from a colder to a hotter body w/o a cost (work). iow e=100% is not possible! Reversible vs irreversible processes. Heat engines: heaters and refrigerators

21. Early heat engines:

23. 4 stroke or Otto engine intake stroke compression stroke ignition power stroke exhaust stroke Bottom right T a, bottom left T b Use T*V  -1 = const. law for the two adiabatic processes For r=8,  = 1.4 e=56%

24. Diesel Cycle Typical r exp ~ 15, r comp ~ 5

25. Carnot Cycle The best-efficiency cycle 2 reversible isothermal and 2 reversible adiabatic processes.

26. There are many other useful state functions: the thermodynamic potentials Enthalpy H = U + PV Free energy at const P, T G = U + PV - TS Free energy at const. T F = U – TS Entropy S etc. The first law revised (for a p-V-T system):  U= TdS - pdV

27. Entropy: Cost of Order – macroscopic interpretation: reversible and irreversible processes Total entropy change zero: reversible Use dQ = S dT in first law!

28. w is no. of possible states Entropy ~ microscopic interpretation

29. The 3 rd Law of Thermodynamics 3 rd Law: It is impossible to reach absolute zero.

30. ‘Fun’ mnemonic about thermodynamic laws: 1 st Law ‘You can’t win, you can only break even’ 2 nd Law ‘You can break even only at absolute zero’ 3 rd Law ‘You cannot reach absolute zero’ Moral: one can neither win nor break even The American Scientist, March 1964, page 40A The laws of thermodynamics give processes a direction