This document summarizes Chapter 2 of a thermodynamics textbook. It discusses properties of pure substances, including their different phases and how they change phases. It describes phase change processes and diagrams used to represent these processes. The summary also discusses equations of state that can be used to model the behavior of substances, like the ideal gas law and more complex equations that account for real gas behavior better. Key concepts covered include saturation temperature/pressure, quality, and using reduced properties and compressibility factors.

1. WCB/McGraw-Hill © The McGraw-Hill Companies, Inc.,1998
Thermodynamics
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Third Edition
2
CHAPTER
Properties of
Pure Substances

2. WCB/McGraw-Hill © The McGraw-Hill Companies, Inc.,1998
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(fig. 2-16)
Constant-Pressure Phase-Change
Process
2-1

3. WCB/McGraw-Hill © The McGraw-Hill Companies, Inc.,1998
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T-v Diagram of a Pure Substance
2-2
(Fig. 2-18)
Energy, not mass, crosses closed-system boundaries

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

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

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

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

8. WCB/McGraw-Hill © The McGraw-Hill Companies, Inc.,1998
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P-v-T Surface of a Substance that
Contracts on Freezing
(Fig. 2-26)
2-7

9. WCB/McGraw-Hill © The McGraw-Hill Companies, Inc.,1998
Thermodynamics
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P-v-T Surface of a Substance that
Expands on Freezing
(Fig. 2-27)
2-8

10. WCB/McGraw-Hill © The McGraw-Hill Companies, Inc.,1998
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Partial List of Table A-4
(Fig. 2-35)
2-9

11. WCB/McGraw-Hill © The McGraw-Hill Companies, Inc.,1998
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Quality Shown in P-v and T-v
Diagrams
(Fig. 2-41)
2-10
Quality is related to the horizontal differences of P-V and T-v diagrams

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

13. WCB/McGraw-Hill © The McGraw-Hill Companies, Inc.,1998
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Pure Substances
can Exist as Compressed Liquids
(Fig. 2-49)
2-12
At a given P and T, a pure substance will exist
as a compressed liquid if T<T sat @ P

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

15. WCB/McGraw-Hill © The McGraw-Hill Companies, Inc.,1998
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Comparison of Z Factors
for Various Gases
(Fig. 2-57)
2-14

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

17. WCB/McGraw-Hill © The McGraw-Hill Companies, Inc.,1998
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Chapter Summary
• A substance that has a fixed chemical
composition throughout is called a pure
substance.
2-16

18. WCB/McGraw-Hill © The McGraw-Hill Companies, Inc.,1998
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Chapter Summary
• 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

19. WCB/McGraw-Hill © The McGraw-Hill Companies, Inc.,1998
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Chapter Summary
• In the gas phase, a substance that is not about to
condense is called a superheated vapor.
2-18

20. WCB/McGraw-Hill © The McGraw-Hill Companies, Inc.,1998
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Chapter Summary
• 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

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Chapter Summary
• In a saturated liquid-vapor mixture, the mass
fraction of the vapor phase is called the quality
and is defined as
The 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

22. WCB/McGraw-Hill © The McGraw-Hill Companies, Inc.,1998
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Chapter Summary
• In the saturated mixture region, the average value
of any intensive property y is determined from
where f stands for saturated liquid and g for
saturated vapor.
2-21

23. WCB/McGraw-Hill © The McGraw-Hill Companies, Inc.,1998
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Chapter Summary
• 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

24. WCB/McGraw-Hill © The McGraw-Hill Companies, Inc.,1998
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Chapter Summary
• 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

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

26. WCB/McGraw-Hill © The McGraw-Hill Companies, Inc.,1998
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Chapter Summary
• 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

27. WCB/McGraw-Hill © The McGraw-Hill Companies, Inc.,1998
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Chapter Summary
• 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 as
where 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

28. WCB/McGraw-Hill © The McGraw-Hill Companies, Inc.,1998
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Chapter Summary
• The deviation from ideal-gas behavior can be
properly accounted for by using the
compressibility factor Z, defined as
2-27

29. WCB/McGraw-Hill © The McGraw-Hill Companies, Inc.,1998
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Chapter Summary
• The Z factor is approximately the same for all
gases at the same reduced temperature and
reduced pressure, which are defined as
where Pcr and Tcr are the critical pressure and
temperature, respectively. This is known as the
principle of corresponding states.
(Continued on next slide)
2-28

30. WCB/McGraw-Hill © The McGraw-Hill Companies, Inc.,1998
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Chapter Summary
• 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
(Continued from previous slide)
2-29

31. WCB/McGraw-Hill © The McGraw-Hill Companies, Inc.,1998
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• The P-v-T behavior of substances can be
represented more accurately by the more complex
equations of state. Three of the best known are
van der Waals:
where
Chapter Summary
2-30

32. WCB/McGraw-Hill © The McGraw-Hill Companies, Inc.,1998
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Chapter Summary
• Beattie-Bridgeman:
where
2-31

33. WCB/McGraw-Hill © The McGraw-Hill Companies, Inc.,1998
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Chapter Summary
• Benedict-Webb-Rubin:
The constants appearing in the Beattie-Bridgeman and Benedict-Webb-
Rubin equations are given in Table A-29 for various substances.
2-32