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I was thinking, if you have a large amount of water, with an uneven solute concentration, diffusion will lead to an even concentration of solute throughout the solution.

Intuitively,that would mean that our system initially has a large amount of potential energy, and that it decreases to a minimum.

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I feel like this raises two questions :

Firstly, from which force does this inital "osmotic" potential energy derive ?

Secondly, under what form is this potential energy realeased once concentration equilibrium is reached ?

What's more, if you consider a cell membrane with a great concentration difference between one side, and another, simple diffusion will lead solute molecules to pass through the membrane. So, in order to pass through the membrane, a solute would have to expend potential energy : the diffusion reaction would have a certain activation energy. Under what form is this energy then dissipated ? It would first become kinetic enrgy, allowing the solute to pass through the membrane, but what form would it then take ? Simply heat energy ?

Any answer would be greatly appreciated, thanks.

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    $\begingroup$ It seems to be a problem of entropy, and not a problem of internal energy. $\endgroup$
    – Maurice
    Dec 26, 2022 at 16:44
  • $\begingroup$ Both entropy and enthalpy of mixing are important and looks like OP hadn't looked up neither. $\endgroup$
    – Mithoron
    Dec 26, 2022 at 18:27

1 Answer 1

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Energy can be recovered across a concentration gradient, as in osmotic power production.

But you ask, if I understand correctly what happens if the energy is not harvested? The same thing that would happen if you dropped a weight:

  • If the weight is attached so as to spin a generator, then the potential energy can be converted to electric energy.
  • If the weight is allowed to impact a surface, instead, then the potential energy is converted to heat.

If economics is considered the dismal science, thermodynamics is equally grim. Consider Ginsberg's Theorem

  1. You can’t win.
  2. You can’t break even.
  3. You can’t get out of the game.
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