The ideal gas EOS can be written in many different ways ...
pV  nRT
R  the universal gas constant
ft-lbf
Btu
J
 1545.35
 1.986
 8.314
lbmol-R
lbmol-R
mol-K
T is the absolute temperature (K or R)
V
p  RT
n

M
pV  nRT 
M
R
pv  RT
ft 3
m3
v  molar specific volume 

lbmol kmol
 R


nM





M

 T  mRT


pV  mRT
R
 mass-based gas constant (not universal)
M
ft 3
m3
V 
p    RT  pv  RT v  mass specific volume 

lbm kg
m
1
v
 p   RT is another form of the ideal gas EOS

1
Given: A sample of room air at 72°F and 14.0 psia
Find: The specific volume and density of the air (mass-based)
using the Ideal gas EOS.
Critical Thinking Questions:
What form of the Ideal gas EOS should you use?
What temperature units should you use in the Ideal gas EOS?
What pressure units should you use in the Ideal gas EOS?
What is the universal molar gas constant?
Which table is this in the Properties Supplement?
What is the mass-based gas constant for air?
Which table is this in the Properties Supplement?
2
Given: A sample of room air at 72°F and 14.0 psia
Find: The specific volume and density of the air (mass-based)
using the Ideal gas EOS
RT
p
T  72  459.67  531.67 R
ft-lbf
1545.35
R
lbmol-R  53.34 ft-lbf

R
lbm
lbm-R
M
28.97
lbmol
pv  RT
 v
 Notice M
ft-lbf 

53.34
  531.67 R 

ft 3
lbm-R 

 14.07
 v
2
lbm
lbf   144 in 

14.0



in 2   ft 2 

 
3
1

v
1
ft 3
14.07
lbm
 0.0711
lbm
ft 3


and R in Table C.13a 