Answer to Question #233008 in Chemical Engineering for Kaa

Question

Urea with formula structure of (NH2)2CO is diffusing very slowly in water solution at 31 oC to 

develop the hydrolysis of urea into carbon dioxide and ammonia. The urea solution was produced 

through the active site with the protein binding (MW = 726 300) containing 21 g protein/200 mL 

solution and form a tetrahedral cluster that fills the cavity site through hydrogen bonds.Compare the diffusivity coefficient for urea solution at 31 oC using Stokes-Einstein and 

Wilke-Chang methods.

Answer 1

In the case of diffusion of urea solution, two equations for estimating the diffusion coefficient are very popular: the Stokes-Einstein equation

where Di in j is the diffusion coefficient of solute i in pure solvent j, k is the Boltzmann persistent, T is the temperature, nSE is the Stokes-Einstein number, ηj is the solvent viscosity, Ri is the radius of the solute molecule, and Rj is the radius of the solvent molecule, and the Wilke-Chang equation: 

Where Di in j is given in cm2/s, n is the Wilke-Chang parameter, x is the connotation parameter, Mwj is the molar mass of the solvent in g/mol, ηj is given in cP and Vbi is the volume of the solute at its usual boiling point in cm3/mol.