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.
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})
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
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