Substituting in the equation, we haveTIP
Least deviations occur at low pressures and high temperatures.
High deviations occur at high pressures and very low temperatures.Ideal Gas Deviations
In the use of the gas laws, we have assumed that the gases involved were “ideal”
gases. This means that the molecules of the gas were not taking up space in the gas
volume and that no intermolecular forces of attraction were serving to pull the
molecules closer together. You will find that a gas behaves like an ideal gas at
low pressures and high temperatures, which move the molecules as far as
possible from conditions that would cause condensation. In general, pressures
below a few atmospheres will cause most gases to exhibit sufficiently ideal
properties for the application of the gas laws with a reliability of a few percent or
better.
If, however, high pressures are used, the molecules will be forced into
closer proximity with each other as the volume decreases until the attractive force
between molecules becomes a factor. This factor decreases the volume, and
therefore the PV values at high pressure conditions will be less than those
predicted by the Ideal Gas Law, where PV remains a constant.
Examining what occurs at very low temperatures creates a similar situation.
Again, the molecules, because they have slowed down at low temperatures, come
into closer proximity with each other and begin to feel the attractive force
between them. This tends to make the gas volume smaller and, therefore, causes
the PV to be lower than that expected in the ideal gas situation. Thus, under
conditions of very high pressures and low temperatures, deviations from the
expected results of the Ideal Gas Law will occur.