Chapter 5

Chapter 5

Single-Phase Systems

Physical PropertiesSources:1) literature (handbook, library or web sources)

2) estimation techniques (correlations or theory)

3) measurement (most expensive but sometimes required)

Liquid and Solid DensitiesTemperature dependence -- modest but sometimes important

Pressure dependence -- usually negligible (incompressible)

Mixtures -- sometimes additive volumes can be assumed

(Can you derive the last two from the first?)

Mixtures -- Nonadditive volumes

Excess Volume (per mole)

large:1) near mixture critical conditions (high T and P)

2) for strongly interacting species (e.g., ethanol + water)

Ideal Gases (sometimes called "perfect gases")

Obey the ideal gas law:

Equation of state -- a relationship between P,

, and T -- the equation above is called the ideal gas equation of state.

Compressibility factor:

definition of z

for ideal gases

Standard conditions:1) scientific0 oC, 1 atm (exact - not 1 sig. fig.)

(to 3 sig. figs.)

1 mol (at std. conditions) ( 22,400 cm3

1 lbmol ( 359 ft3

2) natural gas industry

60 oF, 14.7 psia

1 lbmol ( 379 ft3Calculations:usually involve converting from one set of conditions to another

or

Ideal gas mixtures

Partial pressure of component A:

Note: This is used as the definition of "partial pressure", even for

non-ideal gases. It is equal to the pressure that would be

exerted if A alone occupied the container only for ideal

gases.

Total pressure = sum of partial pressures:

Real Gases (sometimes called imperfect gases)

Equation of state is usually complicated -- compressibility factor not unity.

Virial equation of state -- expansion about ideal gas law:

B, C, ... = 2nd, 3rd, etc., virial coefficients (functions of T)

Cubic equations of state -- all modifications of Van der Waals equation of state:

Van der Waals equation of state

cubic in molar volume

Note: As the molar volume becomes large, z ( 1.

Soave-Redlich-Kwong equation of state

(see Eqn. 5.3-12, p. 203)

Corresponding states approach for compressibility factors

Simple (two-parameter) corresponding states: All fluids obey the

same equation of state written in reduced form.

Since zC is nearly a constant for many organic species (about 0.27), the most often used form is

see charts on pp. 208-11

They also use the following, which is helpful when the

molar volume is known:

Extended (three-parameter) corresponding states

Note: The Pitzer acentric factor is zero for simple species.

Gas mixtures

Use pseudocritical properties -- Kay's rules

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