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Equation of state for non-ideal gases
Equation of state for non-ideal gases
- The P-V-T relationship for real gas needs modification of ideal gas laws.
1) Compressibility factor
The compressibility factor Z is a correction term to the ideal gas laws.
PV=ZRT, z : compressibility factor
– Z can be estimated using the concept of “corresponding states”.
It states that gases behave similarly with respect to non-ideality;
that is, they have the same Z value when they are in corresponding
states relative to their respective critical pressure and critical
temperature.
It states that gases behave similarly with respect to non-ideality;
that is, they have the same Z value when they are in corresponding
states relative to their respective critical pressure and critical
temperature.
– Thus, Z can be determined by knowing reduced pressure P(r), and
reduced temperature T(r).
– The Z values are tabulated (graphed) as a function of P(r), T(r), thus Z
depends on P, T.
(Pr=frac{P}{Pc}, Tr=frac{T}{Tc})
where P, and T are the actual pressure and temperature and Pc
and Tc are the critical values.
and Tc are the critical values.
2) Van der Waals (vdw) equation of state
From ideal gas law, corrections in
① Volume
Real gas has finite volume (ideal gas = volume-less)
→ subtract the gas volume from the total volume.
② Another consideration
Particles are interacting each other. This correction should be considered in the pressure term.
((P)+(frac {a}{V^2})) ((V)−(b))=(RT) (per) (mole)
Interaction correction Volume correction
