Diffusion of Gases

What Is Diffusion?

Before we discuss the diffusion of gases, let’s look at what diffusion is. Diffusion is a net movement of atoms or molecules from a highly concentrated region to a low concentration region. In other words, it is the movement of atoms or molecules from a high chemical potential region to a low chemical potential region.

The word diffusion is derived from the Latin word ‘diffuser’, meaning to spread out, which means a substance that spreads out or moves from one area to another. Diffusion should not be confused with other transport phenomena, like advection or convection, where it uses move particles from one place to another in a bulk motion.

The movement of molecules in solids is very small, relatively large in liquids and very large in gases. And this movement of molecules has led to a phenomenon called diffusion.

Diffusion of Gases

The thermal motion of gas particles above absolute zero temperature is called molecular diffusion. The rate of this phenomenon movement is a function of the viscosity of the gas, temperature and size of the particles. The result of diffusion is a slow mixing of materials where the distribution of molecules or atoms is uniform.

Rate of Diffusion

Here is an example to understand the diffusion of gases. Take a container, separating it into two partitions. Keep two gases, A and B, at the same pressure in two parts of the container. The molecules of gas A and B are in continuous random motion in their respective compartments. Now, remove the partition of the container. The molecules of gas A will begin to stray into gas B due to the random motion. In the same way, the molecules of gas B will begin to stray into gas A due to random motion. As time passes, the molecules of both gases continue to stay with each other. In a period of time, the whole mass of gas in the container will be a homogeneous mixture of gas A and gas, and this results because of the phenomenon called diffusion.