Question

write the equation for flux (J).

Answer 1

The equation for flux is:

where,

·         J is the "diffusion flux," of which the dimension is amount of substance per unit area per unit time, so it is expressed in such units as mol m⁻² s⁻¹. Jmeasures the amount of substance that will flow through a unit area during a unit time interval.

·         D is the diffusion coefficient or diffusivity. Its dimension is area per unit time, so typical units for expressing it would be m²/s.

·         φ (for ideal mixtures) is the concentration, of which the dimension is amount of substance per unit volume. It might be expressed in units of mol/m³.

·         x is position, the dimension of which is length. It might thus be expressed in the unit m.