why do molecules of low molar mass diffuse more rapidly that molecules with highter molar mass?

Question

how are you suppose to prove this with the kinetic molecular theory?

Answer 1

The kinetic theory is KE=1/2mv². If you want the kinetic energy to be constant, any increase in mass must be proportional with a decrease in velocity. Therefore, if two objects with different masses have the same kinetic energy the light one must move faster because it needs a higher velocity to keep the kinetic energy constant.

Answer 2

kinetic energy = 1/2mv^2

At a given temperature, the kinetic energy of particles is distributed equally so only the velocities are changed. lower molar mass implies the particle is moving faster and hence, they can diffuse more rapidly. The velocity of a particle is inversely proportional to the square root of it's mass. i.e., if the mass quadruples, the velocity decreases by 1/√4 or to 1/2. Or we can say if the mass of the particle decreases by 4, its velocity will double at the same temperature.

Answer 3

Look up Graham's Law of Diffusion.