Transcript Chem 300 - Ch 16/#2 Today’s To Do List

Chem 300 - Ch 16/#2
Today’s To Do List





Equations of State catchup
More about the Critical State
Law of Corresponding States
Virial Equations
Intermolecular Potentials(Intro)
How do we show this?

Devise a better equation of
state by:
• Correcting for IG deficiencies.
• Attractive forces
• Excluded volume (repulsive) forces
• Curve-fitting experimental data.
Adjustments to the Ideal
Gas Eq. Of State

Van der Waals Equation:
• P = RT/(Vm - b) - a/V2m
excluded
attractive
•
volume
forces
•

Redlich-Kwong Equation:
• P = RT/(Vm - B) - A/[T½Vm(Vm + B)]
• a, b, A, B depend upon type of gas
Van der Waals
Constants
GAS
He Ne
Ar
Kr
CO2 NH3
a
0.035 0.21
1.36
2.35
3.65
4.22
b
2.37
3.22
3.98
4.27
3.71
1.71
A Real Gas: CO2 (experim.)
Van der Waals(a) &
Redlich-Kwong(b): CO2
Reduced Variables: Tred = T/Tcrit
VdW in Critical terms
 3P V
 P
 V
2
c mc
2
m
 1 
  Vm  Vmc   RT
 3 
Reduced Eq. Of State
3 
1 8

 PR  2   VmR    TR
 VmR  
3 3
Van der Waals & Reduced
Variables
Some Critical Constants
P(atm), V(mL/mol), T(K)
Gas He
Ar
Kr
CO2 NH3 H2O
PC
2.3
48
54
73
111 218
VC
58
75
92
94
72
TC
5.2
151 209 304 405 647
ZC
0.30 0.29 0.29 0.27 0.24 0.22
55
Principle of
Corresponding States
Virial Eq. Of State
and Data Fitting

Z = PVm/RT
= 1 + B2V(T)/Vm + B3V(T)/V2m+ …
• B2V(T) = 2nd virial coefficient

Z = PVm/RT
= 1 + B2P(T)P + B3P(T)P2 + …
• B2V(T) = RT B2P(T)
The 2nd Virial
Coefficient [B(T)]


Shows deviation from gas
ideality (B<0 at low T)
When attractive and repulsive
forces cancel, B = 0, T = TBOYLE
B(T) can tell us about the
intermolecular (IM) forces
affecting different gases
B(T) tells us about the IM
forces affecting a gas at
different T
Next Time





More on IM Forces
A bit on Potential Energy
Lennard-Jones & Other
Potentials
What is a London Dispersion
force??
The return of Van der Waals