Equations of State – How far can we push it?
(16.3,16.4)
Consider the vdW equation of state:
(
)
2
a
P
V
b
RT
V
⎛
⎞
+
−
=
⎜
⎟
⎝
⎠
(
)
(
)
2
2
PV
a
V
b
RTV
+
−
=
3
2
0
RT
a
ab
V
b
V
V
P
P
P
⎛
⎞
−
+
+
−
=
⎜
⎟
⎝
⎠
(
)
Cubic equation in V
3 roots
→
(
)
3
2
0
PV
RT
bP V
aV
ab
−
+
+
−
=
Fig. 16.7
Figure shows that below the critical
point, liquid and gaseous phase of CO
2
can coexist.
c
So, at a given T<T , as you compress the gas,
(G
A) you reach a point where V will change
with essentially no increase in P (A
D), until
all of the gas liquifies.
Then, further compression
requires a hug
→
→
e increase in P (D
L).
→

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