01The model
Gas particles are tiny compared to the space between them, move randomly, collide elastically and have no attractions. Average KE ∝ kelvin temperature.
At the same T, all gases have the same average KE, so lighter gases move faster. The Maxwell–Boltzmann curve flattens and shifts right as T rises.
02Notebook box
KE = ½mv². Same T → same KE → smaller m means bigger v.
Worked example: At 300 K, which is faster, H₂ or O₂? H₂ — same KE, much lower mass.