##  [Fick's First Law](/index.php/ficks-first-law) 

  ##  [Fick's First Law](https://natural.quantumdictionary.io/ficks-first-law-0) 

  

 [![Natural & Formal Sciences Dictionary](/sites/default/files/styles/large/public/2026-01/Natural%20%26%20Formal%20Sciences.png.webp?itok=2kCDRVQv)](/index.php/topic-specific-dictionaries/natural-formal-sciences)



**Natural & Formal Sciences Dictionary**

 







 

 

 

 



 

 

 

 

Definition

A constitutive relation for diffusive transport stating that the particle flux J is proportional to the negative concentration gradient: J = −D ∇C, where D is the diffusion coefficient.

 

 

 

 

 





 

 



 ##  [Fick's First Law](https://engineering.quantumdictionary.io/ficks-first-law-1) 

  

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**Engineering & Applied Technologies Dictionary**

 







 

 

 

 



 

 

 

 

Definition

In a continuum and under steady‑state conditions with negligible bulk convection, the diffusive flux J_i of species i (amount per area per time) is proportional to the negative gradient of its concentration c_i: J_i = -D_i·∇c_i (in one dimension J_i = -D_i·dc_i/dx). D_i is the molecular diffusion coefficient (assumed constant in the simplest form).