The average kinetic energy of the molecules in a gas sample depends only on the temperature, T. However, given the same kinetic energies, a lighter molecule will move faster than a heavier molecule, as shown in the equation for rms speed
rms speed = square root 3RT/M
where R = 8.314 J/(mol•K) and M is molar mass in kilograms per mole. Note that a joule is the same as a kilogram-meter
squared per second squared (kg•m²/s²).
What is the rms speed of Cl₂ molecules at 411 K?
What is the rms speed of He atoms at 411 K?
