Here's why:
* Kinetic Molecular Theory: This theory states that the average kinetic energy of gas molecules is directly proportional to the absolute temperature.
* Kinetic Energy and Speed: Kinetic energy is related to the mass and speed of a molecule. The equation is KE = 1/2 * mv², where KE is kinetic energy, m is mass, and v is speed.
* Temperature and Speed: Since the average kinetic energy is the same for all gases at a given temperature, the heavier molecules (higher mass) must compensate by having a lower average speed to maintain the same kinetic energy.
Example:
At the same temperature, a gas like Xenon (Xe, very heavy) will have a lower average molecular speed than a gas like Helium (He, very light).
