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CHAPTER

2. CHAPTER. Properties of Pure Substances. (fig. 2-16). 2-1. Constant-Pressure Phase-Change Process . (Fig. 2-18). 2-2. T-v Diagram of a Pure Substance. Energy, not mass, crosses closed-system boundaries. (Fig. 2-19) . 2-3. P-v Diagram of a Pure Substance. SUPERHEATED.

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  1. 2 CHAPTER Properties ofPure Substances

  2. (fig. 2-16) 2-1 Constant-Pressure Phase-Change Process

  3. (Fig. 2-18) 2-2 T-v Diagram of a Pure Substance Energy, not mass, crosses closed-system boundaries

  4. (Fig. 2-19) 2-3 P-v Diagram of a Pure Substance SUPERHEATED

  5. (Fig. 2-21) 2-4 P-v Diagram of Substance that Contracts on Freezing

  6. (Fig. 2-22) 2-5 P-v Diagram of Substance that Expands on Freezing

  7. (Fig. 2-25) 2-6 P-T Diagram of Pure Substances

  8. (Fig. 2-26) 2-7 P-v-T Surface of a Substance that Contracts on Freezing

  9. (Fig. 2-27) 2-8 P-v-T Surface of a Substance that Expands on Freezing

  10. (Fig. 2-35) 2-9 Partial List of Table A-4

  11. (Fig. 2-41) 2-10 Quality Shown in P-v and T-v Diagrams Quality is related to the horizontal differences of P-V and T-v diagrams

  12. (Fig. 2-45) 2-11 Partial List of Table A-6

  13. (Fig. 2-49) 2-12 Pure Substances can Exist as Compressed Liquids At a given P and T, a pure substance will exist as a compressed liquid if T<Tsat @ P

  14. (Fig. 2-54) 2-13 The Region Where Steam can be Treated as an Ideal Gas

  15. (Fig. 2-57) 2-14 Comparison of Z Factors for Various Gases

  16. (Fig. 2-66) 2-15 Percent of Error in Equations for the State of Nitrogen

  17. A substance that has a fixed chemical composition throughout is called a pure substance. 2-16 Chapter Summary

  18. A pure substance exists in different phases depending on its energy level. In the liquid phase, a substance that is not about to vaporize is called a compressed or subcooled liquid. 2-17 Chapter Summary

  19. In the gas phase, a substance that is not about to condense is called a superheated vapor. 2-18 Chapter Summary

  20. During a phase-change process, the temperature and pressure of a pure substance are dependent properties. At a given pressure, a substance changes phase at a fixed temperature, called the saturation temperature. At a given temperature, the pressure at which a substance changes phase is called the saturation pressure. During a boiling process, both the liquid and the vapor phases coexist in equilibrium, and under this condition the liquid is called saturated liquid and the vapor saturated vapor. 2-19 Chapter Summary

  21. In a saturated liquid-vapor mixture, the mass fraction of the vapor phase is called the quality and is defined asThe quality may have values between 0 (saturated liquid) and 1 (saturated vapor). It has no meaning in the compressed liquid or superheated vapor regions. 2-20 Chapter Summary

  22. In the saturated mixture region, the average value of any intensive property y is determined fromwhere f stands for saturated liquid and g for saturated vapor. 2-21 Chapter Summary

  23. In the absence of compressed liquid data, a general approximation is to treat a compressed liquid as a saturated liquid at the given temperature, that is,where y stands for v, u, or h. 2-22 Chapter Summary

  24. The state beyond which there is no distinct vaporization process is called the critical point. At supercritical pressures, a substance gradually and uniformly expands from the liquid to vapor phase. 2-23 Chapter Summary

  25. All three phases of a substance coexist in equilibrium at states along the triple line characterized by triple-line temperature and pressure. 2-24 Chapter Summary

  26. Various properties of some pure sub-stances are listed in the appendix. As can be noticed from these tables, the compressed liquid has lower v, u, and h values than the saturated liquid at the same T or P. Likewise, superheated vapor has higher v, u, and h values than the saturated vapor at the same T or P. is a major application area of thermodynamics. 2-25 Chapter Summary

  27. Any relation among the pressure, temperature, and specific volume of a substance is called an equation of state. The simplest and best-known equation of state is the ideal-gas equation of state, given aswhere R is the gas constant. Caution should be exercised in using this relation since an ideal gas is a fictitious substance. Real gases exhibit ideal-gas behav-ior at relatively low pressures and high temperatures. 2-26 Chapter Summary

  28. The deviation from ideal-gas behavior can be properly accounted for by using the compressibility factor Z, defined as 2-27 Chapter Summary

  29. The Z factor is approximately the same for all gases at the same reduced temperature and reduced pressure, which are defined aswhere Pcr and Tcr are the critical pressure and temperature, respectively. This is known as the principle of corresponding states. 2-28 Chapter Summary (Continued on next slide)

  30. When either P or T is unknown, Z can be determined from the compressibility chart with the help of the pseudo-reduced specific volume, defined as 2-29 Chapter Summary (Continued from previous slide)

  31. The P-v-T behavior of substances can be represented more accurately by the more complex equations of state. Three of the best known arevan der Waals:where 2-30 Chapter Summary

  32. Beattie-Bridgeman: where 2-31 Chapter Summary

  33. Benedict-Webb-Rubin: 2-32 Chapter Summary The constants appearing in the Beattie-Bridgeman and Benedict-Webb-Rubin equations are given in Table A-29 for various substances.

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