# How does size of molecule affect diffusion?

Dec 1, 2015

${U}_{r m s} = \sqrt{\frac{3 R T}{M M}}$

#### Explanation:

The root mean square velocity (${U}_{r m s}$) of gas particles is given by the following expression:

${U}_{r m s} = \sqrt{\frac{3 R T}{M M}}$

where,
${U}_{r m s}$ is the rate of diffusion
$R$ is the universal gas constant
$T$ is the temperature in kelvin
$M M$ is the molar mass of the gas

To related this expression to the size of gas particles we can say that bigger size particles will possess high molar mass.

Since, $M M$ is inversely proportional to the ${U}_{r m s}$, thus when $M M$ increases, the ${U}_{r m s}$ will decrease.

Therefore, we can conclude that bigger sized particles (heavy particles) will diffuse slower than lighter particles.