Chemical potential vs hydro-static pressure during osmosis

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Discussion Overview

The discussion centers on the relationship between chemical potential and hydro-static pressure during osmosis, particularly in a system involving a semipermeable membrane separating two solutions of different concentrations. Participants explore whether chemical potential can overcome hydro-static forces and how these concepts interact in equilibrium.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested

Main Points Raised

  • One participant notes that osmosis involves solvent movement from higher to lower chemical potential, raising questions about the implications for hydro-static pressure.
  • Another participant requests clarification on the system setup, indicating that typical analyses focus on systems where exchange occurs solely through membranes.
  • A participant describes a U-tube manometer setup with a semipermeable membrane, where one side has a higher concentration of solute, suggesting that the exchange is limited to the membrane.
  • It is mentioned that the chemical potential of the solvent is influenced by both solute concentration and pressure, and that equilibrium requires equal chemical potential on both sides, implying differing pressures for different solute concentrations.
  • One participant suggests that hydro-static forces arise from the weight of the fluid column, proposing that at chemical equilibrium, gravitational potential energy may balance with chemical potential energy.

Areas of Agreement / Disagreement

Participants express varying views on the interplay between chemical potential and hydro-static pressure, with no consensus reached on how these forces interact during osmosis.

Contextual Notes

The discussion does not resolve the assumptions regarding the definitions of chemical potential and hydro-static pressure, nor does it clarify the mathematical relationships involved in the equilibrium state.

Urmi Roy
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So when osmosis between two solutions (separated by a semipermeable membrane),takes place, the solvent travels from the side where its chemical potential is higher to the side where its chemical potential is lower.
However, this results in a difference of levels of fluids across the membrane.

Doesn't this contradict the laws of hydro-statics? Is chemical potential enough of a driving force to overcome hydro-static forces?

Thanks a lot!
 
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Can you describe the setup of the system you are interested in? Typically one is interested in systems where the exchange takes place only through the membranes.
 
Yeah, I'm just considering a system in which a structure that looks like a u-tube manometer, but with a semipermeable membrane at the bottom of the 'U' shape, which separates 2 solutions and supposed the one on the left is more concentrated. The exchange does take place only via the membrane.
 
Yes, the forces are quite large. The chemical potential of the solvent depends on both the concentration of the solute and the pressure. In equilibrium, the chemical potential of the solvent has to be equal on both sides, hence for different concentrations of the solute, pressure has to be different, too.
 
DrDu said:
Yes, the forces are quite large. The chemical potential of the solvent depends on both the concentration of the solute and the pressure. In equilibrium, the chemical potential of the solvent has to be equal on both sides, hence for different concentrations of the solute, pressure has to be different, too.

The hydro-static forces are basically due to the weight of fluid column, so when chemical equilibrium is established, is it like the gravitational potential energy is just balanced by the chemical potential energy?
 

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