alleryStart learning →How does the mean free path of a gas molecule change as the pressure falls?
AIt stays exactly the same
BIt falls in direct proportion
CIt first rises then falls
DIt increases as pressure drops
Answer & Solution
Correct answer: D. It increases as pressure drops
1. Lower pressure at a fixed temperature means fewer molecules packed into each unit of volume.
2. With fewer neighbours in the way, a molecule travels further before it meets one.
3. So the mean free path increases as the pressure decreases.
4. In a good vacuum the mean free path can grow large enough that a molecule crosses the whole vessel untouched.
_Source: OpenStax Chemistry (CC BY 4.0), Ch 9 "Gases", section 9.4 Effusion and Diffusion of Gases_
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