Significance of intrapellet diffusion

P.B. Weis has developed a criterion for detecting whether intrapellet diffusion may be neglected. The basic assumption is that if , then .

When

Or

Simplifying and squaring,

Now , where r_p is the measured rate and .

Substituting k₁ , . This is known as the Weisz Criteria.

This criterion can be approximately used for most catalytic kinetics though it is derived for a 1^st order reaction. Hence, if criterion , is fulfilled then and there is no intrapellet diffusion limitation.