A slab of thickness has an initial solute concentration profile given by:
where is the distance from the exposed surface (i.e., ) and is the solute concentration in .
The governing equation for unsteady-state diffusion is: .
At the exposed surface concentration is set to . The rear surface (i.e., at ) is insulated. The diffusivity of the solute is to be set by the user (expressed in ). The Demonstration plots the concentration profile in the solute versus position in the slab at various instants.