OTOH I am not entirely convinced they are referring to a single reaction at all, it could be multiple reactions combined into a single law there?
What do you understand by non-elementary?
Multiple reactions combined into a single law :p But let's say we don't have the mechanism for a reaction, we only have the overall thing (but it still goes to completion). Can we express the law in the r=kAx
form or does it need to be something more complicated?
My instinct when I see something non-elementary like A
C is that surely, just like the ODEs we just wrote, we can write 3 more now, one for each species. But if the rate law for each section of the ODE is not of form kAx
then that means more work is needed...