6. Molecular exchange coefficients

Water molecules and species in solution are in a state of permanent agitation. On a microscopic scale, exchanges of movement, heat or matter take place between different points in the solution, but if the solution is homogeneous, it remains so, since these exchanges compensate each other statistically. On the other hand, if differences in flow velocity, temperature or concentration exist between two points, a net transfer of the property concerned takes place in the opposite direction to the gradient. The coefficients that characterize the intensity of these exchanges (balanced or unbalanced) are state functions. For seawater, their values depend strongly on temperature, but very little on salinity and pressure.