chapter08 Real Gases（2）.ppt

Chapter 8
Real Gases
Homework
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General: , , ,
Real Gases
Physical Chemistry
Estimate a molar volume
Estimate the molar volume of CO2 at 500 K and 100 atm by treating it as a van der Waals gas. (the van der Waals coefficients of CO2 are: a= atmL2mol-2, b=10-2 L mol-1)
Answer.
()
Rearrange equation () for a molar volume
Real Gases
Physical Chemistry
Estimate a molar volume
Estimate the molar volume of CO2 at 500 K and 100 atm by treating it as a van der Waals gas. (the van der Waals coefficients of CO2 are: a= atmL2mol-2, b=10-2 L mol-1)
Answer.
Real Gases
Physical Chemistry
Estimate a molar volume
Answer.
Must solve
Real Gases
Physical Chemistry
Estimate a molar volume
Estimate the molar volume of CO2 at 500 K and 100 atm by treating it as a van der Waals gas. (the van der Waals coefficients of CO2 are: a= atmL2mol-2, b=10-2 L mol-1)
Answer.
Solve for the molar volume
For a perfect gas
Real Gases
Physical Chemistry
Equation of State (eos)
The van der Waals and R-K equations are cubic equations of state.
Real Gases
Physical Chemistry
A cubic algebraic equations always has three roots.
Above the critical temperature Tc, two of the roots plex numbers, one will be a real number.
At the critical temperature Tc, three equal real roots.
Below the critical temperature Tc, three unequal real roots.
A cubic equation of states isotherm in the two-phase region below Tc will resemble the dotted line in Fig. .
Condensation
Real Gases
Physical Chemistry
Isotherms of H2O
Vm
400 oC
U
R
J
N
Y
374 oC
300 oC
200 oC
H2O
L + V
L
V
L
G
H
T
S
K
M
W
P
virial equation of state
()
A more convenient expansion is (in many applications)
first second third coefficients
The virial equation is an example of mon procedure in physical chemistry, in which a simple