homemade citric gel..what ratios

[Screwdriver]

I assume it is some sort of “rule of thumb” which has an element of truth to it and there’s no doubt that heat does speed up (most) chemical reactions. With citric though, reactivity tends to decrease after 70C (apparently something to do with the rate of production of hydrogen). How that affects rust removal

Hotter means faster, faster is not always better.

 

[Ross365]

I think the Arrhenius' theory was fairly intellectual for it's time, derived with scientific rationale, but always had limitations. I think that it considers only simple reactions (molecules A and B react and form C) which depend on entirely on heat. Now, with citric on steel, the rule of x2 for every 10'C may work quite well. But a great deal of modern, real-world materials don't fall in to that category. Metal alloys which form protective oxide layers (like stainless) really don't play ball very often; the rates of their reactions may be controlled to a large degree by kinetic factors whereas I think Arrhenius mostly applies to stuff where the reaction depends entirely on thermodynamic factors.

In the days when I earned a living, if someone from engineering came in the chem lab wanting to talk about doing some accelerated testing, my heart always sank .