Pseudo- and quasi-steady state of diffusion

In the case where diffusion is in the quasi-steady state, the flux will be deduced from the following equation  

For diffusion between two planes, the steady flux is therefore quasi-steady and is obtained from relation [3.38]. Since this flux is independent of tlie space, its production by a surface that remains constant will be invariant and therefore the quasi-stead diffusion across a constant surface is pseudo-steady. 

We will therefore assume that quasi-steady diffusion is generally pseudo-steady. 

Application to the calculation of speeds in pseudo-steady state or quasisteady state 

Experience shows that in many cases pseudo-steady state modes are acceptable solutions for the kinetic results of reactions such as the expression of speed as a function of different variables. 

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