# Diffusion rate of gases

What is the effect of temperature on diffusion rate of gases? Do the diffusion rates of gases decrease with an increase in temperature? Why?

I just read it somewhere that the diffusion rate of gases decreases when temperature increases. So i just wanted to know if its true.

Temperature is directly proportional to diffusion rate.

Diffusion, being the dispersion of molecules throughout a space, is affected by the speed of molecules and the density of the space through which the molecules are being dispersed.

An increase in temperature increases the speed at which molecules move at. This is because the average kinetic energy of the gas molecules is proportional to the absolute temperature of the gas. Increased speed will yield faster and more even diffusion.

Average Kinetic Energy of gas molecules = $\frac{3}{2}RT$.

Therefore, decrease in temperature will cause molecules to slow down (due to reduction in average kinetic energy). Hence rate of diffusion decreases.

I hope this helps!

• @MollyCool I want to have a discussion with you on this . Kindly join chat.stackexchange.com/rooms/73715/gas-rate Feb 26 '18 at 14:40
• No worries. Will join now @Tanuj Feb 26 '18 at 14:42

This should be a comment but I don't have enough reputation to comment yet. Diffusion coefficient, as defined by Fick's equation

$$D_\mathrm {AB} =\frac{\text{flux of mass diffusing } (\pu{kg m^-2 s^-1})}{\text{concentration gradient }(\pu{kg m^-4})} = -\frac{J_\mathrm A}{\mathrm dC_\mathrm A/\mathrm dx}$$

increases with temperature as pointed out by @MollyCool.

Your doubt might come from the fact that gas viscosity increases weakly with increasing temperature. And you may know that diffusivity is inversely proportional to viscosity. Note that the increase of kinetic energy of gas molecules has a much larger effect than the weak increase of viscosity and, overall, gas diffusivity will increase with temperature