| A few more definitions... |
|
| A pure substance - |
a substance that is chemically homogeneous with a fixed chemical composition.
gases -
(vapors) | compressible
fluid (flow under stress)
molecules rarely exert forces on each other |
| solids - | incompressible
rigid
dense
strong intermolecular forces |
| liquids - | relatively incompressible
fluid
dense
properties are determined by the intermolecular forces |
|
| boiling point - |
at a given temperature, the temperature above which liquid is no longer present (all vapor). |
|
| freezing point - |
at a given temperature, the temperature below which no liquid is present (all solid). |
|
| Saturation Temperature (new definition for boiling point) - |
| temperature at which vaporization occurs at a given pressure. (this pressure is called the Saturation Pressure)
| saturated liquid - | liquid @ Tsat & psat |
|
| saturated vapor - | vapor @ Tsat & psat |
Liquid @ T < Tsat for a given pressure is called Compressed Liquid
(p > psat for a given T)
Vapor @ T > Tsat for a given pressure is called Superheated Vapor |
|
| Along the vaporization line T & p are dependent properties -
|
| (if one varies, the other cannot vary arbitrarily and still be on the line) |
|
| Quality - |
mass fraction saturated vapor, x
| x = |
mass of sat. vap.
total mass |
= |
mg
mg + mf |
OR |
mg
mg + mi |
subscript "g" ---> saturated vapor
subscript "f" ---> saturated liquid
subscript "i" ---> saturated solid
|
|
| Critical Point - |
point whre sat. liq. & sat. vap. states are identical
2 distinct phases are not present -- 1 phase, fluid
above the critical point we have a supercritical fluid
for a given substance we have a characteristic critial point with a
- critical temperature, Tc
- critical pressure, pc
- critical specific volume, vc
|
|
| Triple Point - |
* intersection of fusion, vaporization, & sublimation lines
* all 3 phases can coexist in equilibrium |
|
The state of a simple pure substance is defined by 2 independent properties (p, v, T, & x).
- note: at saturation,
- p & T are dependent
- v & x are dependent
|
|
 |
|
IDEAL
GASES |
molecules/atoms take up no space
molecules/atoms do not interact |
| To determine if ideal behavior can be expected, look at the state relative to the critial point -
| Tr = | T
Tc | |
T = Tr * Tc |
| pr = | p
pc | |
p = pr * pc |
|
| Ideal gas behavior can be expected for a superheated vapor when the pressure is very low, or when the molecules have high energy (sufficiently high T) and the pressure isn't too high:
(this is a summary of the trends on a compressibility chart -- but more on that on 7/31/01...)
| I. |
if p << pc , I.G. beh. for all T |
| OR |
| II. |
if T >= 2Tc , I.G. beh. for p < ~5pc |
|
| - END |