Is it possible to have an "Eternal reaction" by mixing the products?

[gggnano]

TL;DR Summary

In other words: if you mix the products of 4 different reactants so that the result is the reactants...I will explain...

So this is a very simple concept but I am not explaining it well:

Let's say you have 4 reactants in 2 different reactions (apologies: the symbols I am using do NOT exist, other than the "C" symbol, I just can't find real elements so that I am using just alphabet symbols as an allegory to show my point) , the reactions are separated:

1. Step one: Reaction
reactant A + reactant B -> product C and product D
(this is the first reaction, which produces C and D)

2. Step two: Another reaction between different reactants:
reactant E + reactant F -> product G and product H
(this is a completely different reaction that produces G and H)

3.
Now since you have all 4 products C,D,G,H from both reactions let's assume that once you mix G + C you end up with A and B and once you mix D+H you have E and F. Since you have A, B, E, F with the same mass (law of conservation of mass...) this means you can start the whole process since the very beginning (step one) and the cycle continues ad infintum?

What am I missing and why is this not infinite? Is the issue that the Gibbs free energy gets decreased ? Is the problem that you need to do "work" by moving the mass of the reactants so that they can react again and thus you gain no energy? Is it that you need oxygen or whatever for spontaneous reaction and it needs to be provided all the time? Or is it simply that such a reaction will be impossible, aka: no reactants exist that will create back A,B,E,F spontaneously ? Thank you!

 

[Borek]

Thermodynamics. System will settle down in the lowest spot of the energy landscape and will sit there happily ever after not moving anywhere - unless you supply it with the external energy.

 

[gggnano]

Thermodynamics. System will settle down in the lowest spot of the energy landscape and will sit there happily ever after not moving anywhere - unless you supply it with the external energy.

OK, but what does that mean? After all the temperature increases from 25 to say 1000 degrees and falls to 25 but will increase to 1000 again once the reactants are mixed again? I guess the 'moving' reactants to mix them again will require more external energy so there is no gain from this?

 

[Fra]

But perhaps you have in mind chemical oscillating reactions, there are classical experiments like iodine clocks etc?
See https://en.wikipedia.org/wiki/Chemical_oscillator
https://en.wikipedia.org/wiki/Chemical_clock

It looks like concentrations oscillate, and they do, but the explanation is that the intermediates oscillate, but not indefinitely, only until the overall reactions reaches equilibirum, and this is related to gibbs energy of the overall reaction.

/Fredrik

 

[Borek]

After all the temperature increases from 25 to say 1000 degrees and falls to 25 but will increase to 1000 again once the reactants are mixed again?

I think you missed the part "will sit there happily ever after".

After an isolated system gets to the equilibrium it stays there, period.

 

[Vanadium 50]

Is H₂O + H₂O ⇔H₃O⁺ + OH^- an example? It happens all the time in a glass of water.

If not, what's the difference? In the description with many reactants, I don't think you've clarified things. Just made them more complicated.

 

[gggnano]

Is H₂O + H₂O ⇔H₃O⁺ + OH^- an example? It happens all the time in a glass of water.

If not, what's the difference? In the description with many reactants, I don't think you've clarified things. Just made them more complicated.

You're most likely right...I was thinking something along the lines of:

1. HCL + Na > H2 + Nacl
2. Nacl + K > KCL + NA
3. H2+KCL > HCL+K
4 -> 1. (cycle continues from beginning, step 1)

HCL and Na will easily react obviously yet no idea if mixing ordinary salt with potassium will result in reaction thought I'm sure it's way better than KCL+Na since K is more reactive. The same can be said about hydrogen and "less tasty salt" KCL.

To start the reaction above all it takes is equal amounts of Na, K and HCL.

 

[snorkack]

You're most likely right...I was thinking something along the lines of:

1. HCL + Na > H2 + Nacl
2. Nacl + K > KCL + NA
3. H2+KCL > HCL+K
4 -> 1. (cycle continues from beginning, step 1)

HCL and Na will easily react obviously yet no idea if mixing ordinary salt with potassium will result in reaction thought I'm sure it's way better than KCL+Na since K is more reactive. The same can be said about hydrogen and "less tasty salt" KCL.

To start the reaction above all it takes is equal amounts of Na, K and HCL.

No. That´s the issue of equilibrium.
If reaction 1) goes to the right and K is more active than Na so reaction 2) goes to the right then therefore reaction 3) will NOT go to the right. Since Na reacts with HCl and K is even more reactive, K will also react with HCl, not vice versa.
Also called "detailed balance".