The equation for unsteady-state diffusion is , where is the distance and is the solute concentration. This Demonstration plots the time-evolution of the concentration profile in the solute, for varying coefficient of diffusion and concentration amplitude. The diffusion function is determined as a function of the distance , the diffusion coefficient , and time .

The function is a function of position and time; you can regulate the diffusion coefficient and concentration amplitude . The range of is the interval from -0.4 to 0.4 (relative units on the horizontal axis).