Fick’s First Law: Definition, Derivation And Application

What is Fick’s law of diffusion?

Fick’s law of diffusion explains the diffusion process (movement of molecules from higher concentration to lower concentration region). In 1855, Adolf Fick described the Fick’s Law of Diffusion. A diffusion process that obeys Fick’s laws is called normal diffusion or Fickian diffusion. A diffusion process that does NOT obey Fick’s laws is known as Anomalous diffusion or non-Fickian diffusion.

Fick’s Law describes the relationship between the rate of diffusion and the three factors that affect diffusion. It states that ‘the rate of diffusion is proportional to both the surface area and concentration difference and is inversely proportional to the thickness of the membrane’.

The net diffusion rate of a gas across a fluid membrane is proportional to the difference in concentration, to the surface area of the membrane, to the permeability of the membrane to the substance, and inversely proportional to the thickness of the membrane and molecular weight of the molecule.

This principle is illustrated by opening a perfume bottle in the corner of a closed room. If you wait long enough, the perfume odor will permeate the room because the perfume molecules have diffused from one side of the room to the other, from a region of high concentration to a region of low concentration.

Fick’s First Law

Movement of solute from higher concentration to lower concentration across a concentration gradient.J=−DdφdxJ=−Ddφdx


J: diffusion flux

D: diffusivity

φ: concentration

x: position

Application of Fick’s law

Biological application:

(from Fick’s first law)
P: permeability

c2-c1: difference in concentration


Fick’s law is applicable for two miscible liquids when they are brought in contact and diffusion takes place at a macroscopic level.

Fabrication of semiconductor:

Diffusion equations from Fick’s law are used to fabricate integrated circuits.

Pharmaceutical application

Fick’s law applied in medical science for the purposes of research and development in healthcare industries.

Applications in food industries.

Fick’s law also applied in food industries. Leaching and drying are normally controlled by internal diffusion.