Applicability of the Ideal Gas EOS

Ch 2, Lesson E, Page 3 - Applicability of the Ideal Gas EOS

• Experiments have shown that the Ideal Gas EOS is a better approximation of the PVT behavior of real gases at high temperatures and low pressures.
• It is easier to just say that gases behave more ideally when the have a large molar volume.
• Does that make sense ?
• You probably recall that an ideal gas at standard temperature and pressure has a molar volume of 22 .4 L/mole.  But could we accurately model a real gas, like air, as an ideal gas at STP ?
• Strictly speaking, an ideal gas is one in which each molecule remains unaffected by the presence of any other molecules.
• So, if the universe consisted of just ONE molecule, it would be an ideal gas.
• How does that help ?
• Well, as the molar volume increases, the average volume associated with each molecule increases.  So does the distance that a molecule travels before colliding with another molecule.
• The bottom line is that the larger the molar volume, the less the molecules interact with each other.
• So, the question boils down to this: when is the molar volume large enough that the ideal gas EOS is accurate to the precision typically required in engineering problems ?