Summary & Keys of Chap. 3

Fig. 3.1 Physical system – piston/cylinder arrangement showing const-pressure change from liquid to vapor phase for a pure substance.

Fig.3.2 diagram for showing liquid/vapor two-phase saturated states – need χ

Saturated temperature/pressure

T OH 2

• Subcooled/compressed liquid

• Superheated vapor

• Liquid/vapor 2-phase region

f

sat

sat

PtempgivenPTpressuregivenT

.

.

)()(

g

sat

sat

PtempgivenPTpressgivenT

.

.

)()(

gf

satsatsatsat PTorTP

)()( ..

• The vapor-pressure curve (i.e.vaporization line or sat. press-sat. temp relation, Fig. 3.2) is just a part of P-T (phase) diagram (Fig.3.5) for a pure substance where … solid, liquid and vapor phases may exist together in eq’m ---- sublimation line: solid and vapor phases are in eq’m ;fusion line: solid and liquid phases are in eq’m….all three phases in eq’m at the Triple-point....And the critical point is when…

• All pure substance exhibit same general behavior e.g. the , diagrams. However, the critical and triple-point data vary greatly from one substance to another.

• Q, Why the horizontal line (const-press) process shown in Fig 3.5? Why not const-temp process?

• Why solid is commonly referred to as dry ice ?• Note the paragraph in Ex.3.3 …. appropriate

phase boundary value…• Top of P.47, Listing of Tables of (e.g. steam)

and other substances

T TP

2CO

OH 2

• Tables B: , refrigerants, • Table A1, conversion factors; A2,critical

constants, A3 A4, selected..properties..substances A5, properties of ideal gases; A6, ….

• Bottom P.47, Tables of compressed Table B.1.4 And when compressed-liquid data are not available.

• Table B.1.5 gives the properties of sat. solid and sat. vapor (i.e. sublimation), and all pressures, as expected, less than the corresponding triple-point pressure.

• Best examples Ex 3.1 ~ Ex 3.7.

OH2 2N

pCOH2

• Ex 3.6…Table B.6.1 with T=220K, which is higher than the critical T in the last entry, then, Table B.6.2 is superheated Table.Table B.6.1 is saturated Table.e.g. , ,

2N2N

f g kTsat 37.96

• Chap. 3.5 thermodynamic surfaces are shown in Fig.3.18 (substance that expands on freezing) Fig3.19 (substance that contracts on freezing). or

• Solid,liquid and vapor phases are the curved surfaces

• Two-phase regions are the ruled surfaces(lines of const-press are also lines of const-temp)

TP

),( TP ),( TPP ),( PTT

• Therefore, the (P-T) phase diagram is the projection of the surface on the P-T plane (why const-p and const-T process for these 2-phase regions)

• Finally, testing your understanding of Chap. 3.5 by reading the last para. of P.55 (Hint: the solid state is to the left of the liquid state in Fig. 3.19 but it is to the right of the liquid state in Fig. 3.18)

TP