Fick's Law Of Diffusion

What is Fick’s law of diffusion?

Fick’s law of diffusion explains about diffusion process (movement of molecules from higher concentration to lower concentration region) to solve diffusion coefficient derived by Adolf Fick in the year 1855.

There are two laws that are interrelated ie; Fick’s first law is used to derive Fick’s second law which is similar to the diffusion equation.

Fick’s first law

Movement of solute from higher concentration to lower concentration across a concentration gradient.

\(J = -D\frac{\mathrm{d} \varphi }{\mathrm{d} x}\)


    J: diffusion flux

    D: diffusivity

    φ: concentration

    x: position

Fick’s second law

Prediction of change in concentration along with time due to diffusion.

\(\frac{\partial \varphi }{\partial t} = D \frac{\partial^2 \varphi }{\partial x^2}\)


    D: diffusivity

    t: time

    x: position

    Φ: concentration

Application of Fick’s law

  • Biological application:
  • \(flux = -P(c_{2}-c_{1})\) (from Fick’s first law)


    P: permeability

    c2-c1: difference in concentration

  • Liquids: 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
  • Applications in food industries.

Stay tuned with BYJU’S to know more on diffusion and other related topics.

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