Fick’s First Law

[latex]J_{diff} = -D \frac{\delta [ion] }{\delta x} \\ \text{where} \\ \text{J is diffusion flux (molecules / sec-cm}^2) \\ \text{D is the diffusion coefficient (cm}^2 \text{ / sec)} \\ \text{[ion] is the concentration of ion (molecules / cm}^2)[/latex]