The concept of an ideal gas law which was stated earlier in Sect. 2.3 of this chapter was based on assumptions which do not hold in the real atmosphere in which molecules occupy some finite space, however small it may be, and there are also intramolecular forces. It was left to Van der Waals (1837-1923) who carefully reviewed these assumptions and suggested the following modified version of the equation of state for a real gas:
where a and b are constants and R' is a modified Gas constant, somewhat different from R*, the universal gas constant. However, it can be shown that as long as the temperature T remains appreciably above the point of liquefaction of a gas, the difference between the ideal gas law and the Van der Waals' equation is negligible in meteorology.
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