Ideal Gas Model
• For many gases, the ideal gas assumption is valid and the P-v-T
relationship can be simplified by using the ideal gas equation of
state:
Pv=RT (Compressibility factor Z=1)
• For an ideal gas, it can be shown that the specific internal
energy u is a function of temperature only, u=u(T)
• Accordingly, specific enthalpy is a function of temperature
only, since h(T)=u(T)+pv=u(T)+RT
• Physically, a gas can be considered ideal only when the
intermolecular forces are weak.
This usually happens in low
pressure and high temperature ranges.
c
du
dT
c
dh
dT
d u
Pv
dT
d u
RT
dT
c
R
c
c
R
v
P
v
P
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=
=
=
+
=
+
=
+
=
+
,
(
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