Do Catalysts Violate the Second Law of Thermodynamics?

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Nov 13, 2021, 11:14:49 AMNov 13
An obviously absurd consequence of the second law of thermodynamics is that a catalyst speeds up the forward and reverse reactions equally (by exactly the same factor):

"In the presence of a catalyst, BOTH THE FORWARD AND REVERSE REACTION RATES WILL SPEED UP EQUALLY, thereby allowing the system to reach equilibrium faster. However, it is very important to keep in mind that the addition of a catalyst has no effect whatsoever on the final equilibrium position of the reaction. It simply gets it there faster. [...] If the addition of catalysts could possibly alter the equilibrium state of the reaction, this would violate the second rule of thermodynamics..."

Actually, things are far from "equally". Here is a catalyst that speeds up the forward reaction, 2H+ → H_2, but SUPPRESSES the reverse reaction, H_2 → 2H+ (violation of the second law of thermodynamics par excellence):

Yu Hang Li et al. Unidirectional suppression of hydrogen oxidation on oxidized platinum clusters

An analogous example (the forward and reverse reactions are not sped up "equally"):

"In 2000, a simple, foundational thermodynamic paradox was proposed: a sealed blackbody cavity contains a diatomic gas and a radiometer whose apposing vane surfaces dissociate and recombine the gas to different degrees (A_2 ⇌ 2A). As a result of differing desorption rates for A and A_2 , there arise between the vane faces permanent pressure and temperature differences, either of which can be harnessed to perform work, in apparent conflict with the second law of thermodynamics."

Scientists should have noticed the obvious absurdity of this particular consequence of the second law of thermodynamics long ago. Consider the dissociation-association reaction

A ⇌ B + C

which is in equilibrium. We add a catalyst and it starts splitting A - the rate constant of the forward (dissociation) reaction increases by a factor of, say, 745492. If the second law of thermodynamics is obeyed, the catalyst must increase the rate constant of the reverse (association) reaction by exactly the same factor, 745492. But this is insane! The reverse reaction is entirely different from the forward one - B and C must first get together, via diffusion, and only then can the catalyst join them to form A. Catalysts don't speed up diffusion!

See more here:

Pentcho Valev
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