1. Chapter 20 Entropy and the Second Law of Thermodynamics
In this chapter we will introduce the second law of thermodynamics. The following topics will be covered:
Reversible processes Entropy The Carnot engine Refrigerators Real engines
(20–1)

2. Example 1:
An isothermal process is one in which Ti = Tf which implies ln (Tf /Ti) = 0. Therefore, Eq leads to

3. Example 2:
(a) The energy absorbed as heat is given by Eq Using Table 19-3, we find
We use the following relation derived in Sample Problem 20-2:
(b) With Tf = K and Ti = K, we obtain

5. Example 3:

6. (b) Now temperatures must be given in Kelvins: Tai = 393 K, Twi = 293 K, and Tf = 330 K. For the aluminum, dQ = macadT and the change in entropy is
(c) The entropy change for the water is
(d) The change in the total entropy of the aluminum-water system is
DS = DSa + DSw = J/K J/K = +2.8 J/K.

7. Example 4:
(a) This may be considered a reversible process (as well as isothermal), so we use DS = Q/T where Q = Lm with L = 333 J/g from Table Consequently,
(b) The situation is similar to that described in part (a), except with L = 2256 J/g, m = 5.00 g, and T = 373 K. We therefore find DS = 30.2 J/K.

8. Example 5:

18. Example 7:

19. Example
A particular engine has a power output of 5000 W and an efficiency of 25%. If the engine expels 8000 J of heat in each cycle, find (a) the heat absorbed in each cycle and (b) the time for each cycle
10,667 J
2667 J
0.53 s

20. Example
The efficiency of a Carnot engine is 30%. The engine absorbs 800 J of heat per cycle from a hot temperature reservoir at 500 K. Determine (a) the heat expelled per cycle and (b) the temperature of the cold reservoir
240 J
560 J
350 K

21. Example
An automobile engine has an efficiency of 22.0% and produces 2510 J of work. How much heat is rejected by the engine?

24. (20–11)

28. Example 10:

29. Example 11:

30. Example 12:

31. Example 13:

32. Example 14:

33. Example 15:

34. Example 16:

35. Example 17:

36. Example 18:

37. Example 19:

38. Example 20:

39. Example 21:

40. Example 22:

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42. Example 24:

43. Example 25:

44. Example 26:

45. Example 27:

46. Example 28:

47. Example 29:

48. Example 30:

49. Example 31:

50. Example 32:

51. Example 33:

52. Example 34:

53. Example 35:

54. P38

55. P74