Final answer:
Steady state diffusion involves a constant concentration gradient and flow rate, while non-steady diffusion features a changing concentration gradient over time. Steady state is described by Fick's first law and non-steady by Fick's second law, reflecting the time-dependent changes in concentration.
Step-by-step explanation:
The difference between steady state and non-steady (transient) diffusion is that steady state refers to a situation where the flow of a substance does not change over time, while in non-steady diffusion, the substance's flow rate changes as it moves from areas of higher concentration to areas of lower concentration. In a steady state diffusion, the concentration gradient remains constant because the rate at which the substance enters a volume is equal to the rate at which it exits. The schematic for steady state would show a consistent flow with no buildup of substance in any part of the system.
In contrast, non-steady diffusion is characterized by a changing concentration gradient over time. Here, a schematic would show varying degrees of concentration across the system, with the gradient diminishing as the substance moves towards equilibrium.
A mathematical representation of steady state diffusion is given by Fick's first law of diffusion, J = -D(dC/dx), where J is the diffusion flux (amount of substance per unit area per unit time), D is the diffusion coefficient, and dC/dx is the concentration gradient. In non-steady diffusion, Fick's second law is used, which accounts for the time dependency of the concentration gradient: ∂C/∂t = D(∂²C/∂x²).