When something burns on stove, atoms of burnt food starts spreading in kitchen by random atomic motion by process of diffusion. The burnt food atoms start moving from places where ir concentration is high to regions of low concentration.

Interstitial diffusion occurs for smaller impurities like Carbon, Oxygen, Hydrogen etc. For larger species vacancy diffusion is more common.

Net direction of diffusion depends on concentration of particles in a particular region of space and hence concentration gradient is defined as rate of change concentration of particles in a given sample with respect to time.

In homogeneous mixture diffusion and net diffusion are same but in case of in homogeneous materials effect of diffusion is seen to be changing in concentration with time and hence in this case net diffusion and diffusion values are different.

The concentration of diffusing species is directly proportional to position. Hence graph is a straight line with negative slope.

Concentration gradient is major driving force behind diffusion. It is slope of concentration profile and measures difference in concentration of diffusing species per unit length.

Diffusion rate is high for open crystal structure, material with low density as re is a sample amount of free space to diffuse into and material with low melting temperature as particles reach liquid state faster and hence diffusion rate increases. On or hand, rate of diffusion for materials with covalent bond is slower because y are stronger bonds.

Osmosis is a special type of diffusion where an SPM separates two liquid solutions. Solutes cannot pass through SPM. As more solvent particles are present in dilute solution than concentrated one, se particles move through SPM from former to latter.

When a gas at constant pressure pervades through a thin walled metal foil, steady state diffusion occurs. Hydrogen is purified by making it pass through a palladium cap after going through steady state diffusion.

According to Fick’s second law, rate of change of concentration of diffusing species with time at a given point in space is proportional to slope of concentration gradient curve at that point.