For the mass transfer there is Fick's first law D 4 AB A the molar diffusion flux of a in a binary system D AB mass diffusivity; p mass density Molar diffusion flux=mass diffusivity* density gradient Assumption of Constant C and dab in a binary system with chemical reaction, the molar diffusion differential equation DARO 2 )+R ay az RA- the molar rate of production AjA- -----the molar diffusion flux of A in a binary system; DAB ----- mass diffusivity; ------- mass density; Molar diffusion flux = mass diffusivity density gradient Assumption of Constant C and DAB in a binary system with chemical reaction, the molar diffusion differential equation: RA ------ the molar rate of production A dy d j D A A AB  = −  For the mass transfer, there is Fick’s First Law:  A A A A AB A R z c y c x c D Dt Dc +   +   +   = ( ) 2 2 2 2 2 2