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.

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.

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

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.

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.

Rate of diffusion is directly proportional to temperature and it is indirectly proportional to molecular weights.

The concentration gradient varies with time for non-steady state diffusion. Meanwhile, it remains constant for steady state diffusion.

The diffusivity of copper in copper at 500 °C is 1e^-18 while diffusivity at 1000 °C is 2e^-13. By dividing values, we find that diffusivity increases by 200000 times fold.

The diffusion rate is inversely proportional to distance from which particles are diffusing. Larger diffusion distance, rate of diffusion is slower and vice versa.