Question

Using Noyes Whitney equation, explain how certain factors affect the rate of mass transfer of solute particles into a solvent (rate of dissolution).

Answer:

Noyes Whitney equation states that the rate of mass transfer of solute particles into the continuous phase (rate of dissolution) is equal to

dm/dt = DACs/h

where dm/dt = rate of mass transfer / rate of dissolution

D = diffusion coefficient

A= surface area of solute particles

Cs = concentration of solute particles at the boundary layer

h = height of the boundary layer

Noyes Whitney equation states that the rate of dissolution is directly proportional to the the surface area of the solute particle, diffusion coefficient and the concentration of solute particles present at the boundary layer. Simply put, the higher the value of the diffusion coefficient, the greater the surface area and the more concentrated the solute particles at the boundary layers are, the higher the rate of dissolution. On the other hand, according to the equation the height of the boundary layer is indirectly proportional to the rate of dissolution, so the lower the height the faster the rate of dissolution.

In short, the factors that affect the rate of dissolution according to Noyes Whitney equation are: the Diffusion coefficient, the surface area of the solute particle, the concentration of the solute particles at the boundary layer and the height of the boundary layer.

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