Gases

Deviation from Ideal Behavior


Deviations from Ideal Behavior

All real gasses fail to obey the ideal gas law to varying degrees

The ideal gas law can be written as:

For a sample of 1.0 mol of gas, n = 1.0 and therefore:

Plotting PV/RT for various gasses as a function of pressure, P:

Deviation from ideal behavior is also a function of temperature:

Two of the characteristics of ideal gases included:

Real molecules, however, do have a finite volume and do attract one another

The van der Waals Equation

van der Waals equation:

Substance

a (L2 atm/mol2)

b(L/mol)

He

0.0341

0.0237

H2

0.244

0.0266

O2

1.36

0.0318

H2O

5.46

0.0305

CCl4

20.4

0.1383


Example

Use the van der Waals equation to calculate the pressure exerted by 100.0 mol of oxygen gas in 22.41 L at 0.0C

V = 22.41 L

T = (0.0 + 273) = 273K

a (O2) = 1.36 L2 atm/mol2

b (O2) = 0.0318 L /mol

P = 117atm - 27.1atm

P = 90atm

 


1996 Michael Blaber