01When gases misbehave
Real gases deviate at high pressure (particle volume matters) and low temperature (attractions matter). Polar or large gases deviate most.
Attractions make measured P lower than ideal; particle volume makes measured V larger than ideal.
02Notebook box
Most ideal: high T, low P, small nonpolar gas (He).
Worked example: Why does NH₃ deviate more than He? NH₃ hydrogen-bonds; He barely attracts anything.