Lesson 6: 3.6 Deviations from Ideal Gas Law

When and why does the ideal gas law fail to predict the true behavior of a gas?
How do particle volume and intermolecular forces alter the measured pressure and volume of a real gas?

Ideal Gas Deviation
Van der Waals Attractions
Finite Volume
Low Temperature
High Pressure

Learning Objective 3.6.A; Suggested Skill 4.E (Model Analysis - Explain deviations).

Real gases deviate most from ideal behavior at high pressures (where particle volume becomes significant relative to container volume) and low temperatures (where particles slow down enough for intermolecular attractions to pull them together). Gases with strong IMFs show the greatest deviation.

Support: Contrast the concept of an "Ideal Gas" (imaginary, point masses, zero attractions) with a "Real Gas" (has volume, sticky interactions) using a two-column comparison chart.
Extension: Have students look at the van der Waals equation and explain what the constants a (IMF correction) and b (particle volume correction) physically modify in the standard PV=nRT frame.

Under identical conditions of high pressure (50 atm) and low temperature (150 K), a sample of Water vapor (H2O) deviates significantly more from ideal gas behavior than a sample of Methane gas (CH4). Explain the molecular reasoning behind this difference.