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The Principles of Thermodynamics
book

The Principles of Thermodynamics

by N.D. Hari Dass
October 2013
Intermediate to advanced content levelIntermediate to advanced
352 pages
13h 56m
English
CRC Press
Content preview from The Principles of Thermodynamics
234 The Principles of Thermodynamics
vdW pressure is always greater than the ideal gas pressure. In the interesting
cases where both the parameters are non-vanishing, it can go both ways. Let
us compute the difference in the pressures
P
ideal
P
vdW
=
RT
V
RT
V b
+
a
V
2
=
RTb
V (V b
+
a
V
2
(12.23)
It is easy to see that the ratio r = (a(V b)/RTV b) determines the required
answer, i.e P
ideal
> P
vdW
if r > 1, the two pressures equal if r = 1 and P
ideal
< P
vdW
if r < 1. The constant b for many known gases is very small compared to 10
L, so we can approximate r to just (a)/(RTb). It should be appreciated that
this is not the same as ignoring b in the vdW pressure formul ...
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Publisher Resources

ISBN: 9781466512085