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LIVE LAB 18 • STATES OF MATTER & KINETIC THEORY
Compare effusion, diffusion and molecular-speed distributions in an interactive gas lab, then connect rate ratios with molar mass and temperature.
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COMPLETE CONCEPT GUIDE
Connect particle motion with measurable gas behaviour. The lab compares effusion through a small aperture, diffusion in a tube, molecular-speed distributions and the effects of molar mass and temperature.
Effusion is the escape of gas particles through a very small opening. Under matched conditions, the molar effusion rate varies inversely with the square root of molar mass.
For gases 1 and 2 at the same temperature, pressure and aperture conditions, r₁/r₂ = √(M₂/M₁). The lighter gas therefore effuses faster.
Using rounded molar masses of 4 and 32 g/mol, helium effuses √(32/4) = √8 ≈ 2.83 times as fast as oxygen under matched conditions. For equal amounts, effusion times have the inverse ratio: tHe/tO₂ ≈ 0.354.
Diffusion is the net mixing produced by random molecular motion. Tube-distance comparisons use Graham’s relation as a simplified model under carefully matched conditions.
A gas contains particles with a range of speeds. Raising temperature shifts and broadens the Maxwell–Boltzmann distribution, while increasing molar mass shifts it toward lower speeds.
GRAHAM’S LAW FAQ
Under matched conditions, the effusion rate of a gas is inversely proportional to the square root of its molar mass.
At the same temperature, lighter gas particles have a higher characteristic molecular speed, so more of them reach and pass through a small aperture per unit time.
Effusion is escape through a very small opening, while diffusion is mixing caused by random molecular motion through space or another gas.
For a fixed gas, characteristic molecular speeds are proportional to the square root of absolute temperature.
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