# How does molecular weight affect the rate of diffusion?

At equal temperatures, lighter particles will diffuse more rapidly than heavier particles.

#### Explanation:

Diffusion is the movement of particles from where they are more concentrated to where they are less concentrated.

The average kinetic energy of a particle (KE) gives us the temperature of a substance.

KE = $\frac{1}{2} m {v}^{2}$

If we have two gases (A and B) with gas A being heavier than B. The kinetic energy of the two gases will be the same if the gases are at the same temperature.

$K {E}_{A} = K {E}_{B}$

So at equal temperatures, a lighter particle (B) must have a greater velocity (speed) and a heavier particle (A) must have a lower speed.

$\frac{1}{2} {m}_{A} {\left({v}_{A}\right)}^{2}$ = $\frac{1}{2} {m}_{B} {\left({v}_{B}\right)}^{2}$

Here is a video which gives further explanation of this topic. It discusses effusion, which is basically the diffusion of particles through a small opening in a container.

Hope this helps!