How does the molar flux relate to the direction of diffusion for equimolar counter diffusion?

In the scenario of equimolar counter diffusion, the concept of molar flux pertains to the movement of two different species in opposite directions at equal rates. This situation arises when two gases or substances diffuse towards each other in a confined space, and the total amount of each substance does not change.

The key aspect of equimolar counter diffusion is that the molar fluxes of the two species are equal in magnitude but opposite in direction. This means that as one species moves in one direction, the other species moves in the opposite direction with the same rate. This counter flow is essential to maintain a balance or equilibrium in the system, ensuring that the concentration gradients remain stable over time.

This understanding of molar flux is grounded in Fick's laws of diffusion, which describe how particles move from areas of higher concentration to areas of lower concentration. In equimolar counter diffusion, when two different components are diffusing into each other's regions, they effectively create an equalization of concentration, which is represented by their equal and opposite fluxes.

Hence, the correct answer highlights the nature of their movement: the two species flow equally but in opposite directions, reflecting the principles of diffusion in a system where the concentration of each substance remains constant over time.