Gas State: Ideal Gas Theory and Deviations

Lecture 12

Simpler models are more useful than

complex onesas long as they explain the

data.

Deviation of real gases from ideal gas

behavior

The reasons of the deviations:At moderately high pressure, values of PV/RT lower than ideal are due to intermolecular attractions.At very high pressure, values of PV/RT greater than ideal are due predominantly to molecular volume.

To accurately describe real gas behavior, the ideal gas equation has to be redesigned:To adjust pressure up, we need to add a factor that accounts for intermolecular attractions.To adjust the measured volume down, we need to subtract a factor from the entire container volume that accounts for the molecular volume.

Johannes Diderik van der Waals (1837–1923), a Dutch scientist

The van der Waals equation

describes real gas behavior.Herein, a and b are van der

Waals constants.

a and b are specific for every individual

gas.a relates to the number of electrons, which relates to the complexity of a molecule

and the strength of its intermolecular attractions.

b relates to molecular volume.

Van der Waals constants

THE END