Chemistry · Chapter 9

Molecular Speeds, Effusion and Real Gases

Heat a gas and its speed curve slides right and flattens. Make the gas heavier and the curve pulls back and sharpens. Everything on this page comes from one idea: temperature sets energy, so mass sets speed.

Maxwell-Boltzmann speed curve area stays the same

The spread of molecular speeds for the gas and temperature you chose particle speed (m/s) share of particles

Particles in a box speed follows the slider

The chosen gas and the comparison gas moving side by side

Both boxes sit at the same temperature, so both hold the same average kinetic energy. Only the speeds differ.

Set the conditions

m/s root-mean-square
Most probable speed
Average speed
Root-mean-square speed
Kinetic energy per mole

Effusion by Graham's law

Relative effusion rates of the two gases

Effusion is escape through a pinhole. The rate ratio never depends on temperature, because both gases warm by the same amount.

Real gas check

Ideal pressure, RT/V
Van der Waals pressure
Compressibility factor Z