Explanation:

* Kinetic Energy: The average kinetic energy of molecules is directly proportional to temperature. At a given temperature, all molecules have the same average kinetic energy.

* Molecular Mass: Kinetic energy is related to the mass and velocity of a molecule: KE = 1/2 * mv², where KE is kinetic energy, m is mass, and v is velocity.

* Velocity: For a given kinetic energy, a smaller mass (small molecule) will have a higher velocity than a larger mass (large molecule).

In simpler terms:

Imagine two cars with the same amount of power (kinetic energy). The smaller car will be able to accelerate faster and reach a higher speed than the heavier car. Similarly, small molecules, with less mass, can move faster than large molecules at the same temperature.

Exceptions:

There are some exceptions to this general rule, such as:

* Diffusion: In some cases, large molecules can diffuse faster than small molecules due to factors like concentration gradients and the presence of other molecules.

* Special Conditions: Under specific conditions, such as high pressure or low temperature, the movement of large molecules may be affected.

Conclusion:

In general, smaller molecules move faster than larger molecules at the same temperature due to their lower mass and higher velocity. This is a fundamental principle in chemistry and physics.