
where n
i
¼ amount of substance, i, C
i
¼ concentration of component, i,andk ¼ diffusion
coefficient. It will be shown later that this e qu ation is not as accurate as o ne proposed by
Hartley, in which the gradient of the ratio of chemical potential to temperature is used as the driv ing
potential.
Other similar relationships occur in physics and chemistry but will not be given here. The three
equations given above relate the flow of one quantity to a difference in potential: hence, there is a flow
term and a force term as suggested by Eqn (20.4). It will be shown that although Eqns (20.5)–(20.7)
appear to have the correct form, they are not the most approp ...