Diffusion, molecules will flow from high concentration to low

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Discussion Overview

The discussion revolves around the process of diffusion, particularly focusing on the movement of molecules from areas of high concentration to low concentration. Participants explore the underlying mechanisms, including thermodynamic principles and physical forces, as well as the concept of Brownian motion.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested

Main Points Raised

  • One participant questions the explanation of diffusion by suggesting that physical forces must act on ions to move them from one area to another, rather than relying solely on random motion.
  • Another participant asserts that ions move randomly and that this random motion leads to a uniform distribution over time, which is a more probable state.
  • A participant introduces the concept of Brownian motion as the random motion of particles, but another participant challenges the understanding of this phenomenon, suggesting it is not fully comprehended.
  • There are claims about the modeling of Brownian motion, with some participants stating it can only be modeled in one dimension, while others argue that it can be effectively modeled in three dimensions despite some issues.

Areas of Agreement / Disagreement

Participants express differing views on the mechanisms of diffusion, the role of random motion, and the modeling of Brownian motion. There is no consensus on these points, indicating ongoing debate and uncertainty.

Contextual Notes

Participants reference various models and their limitations, particularly regarding the dimensionality of Brownian motion models. The discussion highlights unresolved aspects of these models and their applicability.

kbm
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This might be a stupid question, but it has me kind of confused. In diffusion, molecules will flow from high concentration to low concentration, and the explanation typically given is that in the laws of thermodynamics there is a net increase in entropy over time.

But I am trying to think of it from a perspective of physical forces acting on the molecules...

So say there is an aquarium type thing with a mesh screen separating it into two halves, and a bunch of some solute, say salt, is dumped into one side of it. By diffusion, after some time, there will be net movement of the solute molecules from the side they were dumped on into the other side. What I am confused about is, if the ions are in an area of relatively little motion, then to move to a completely different area would require some outside force acting on the ions themselves to propel them to the new area, wouldn't it?
 
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No. Ions always move at random. It happens that as effect of these random motions they tend to be uniformly distributed, as such distributions are much more probable.

Go here:

http://www.chembuddy.com/?left=all&right=download

Scroll down and download diffusion program. Ions are always added on top, and just by random motions they reach the bottom.
 


And if you were interested, the random motion is Brownian motion, which, like most science, no-one really understands.
 


Kracatoan said:
And if you were interested, the random motion is Brownian motion, which, like most science, no-one really understands.

Care to elaborate? As far as I know Brownian motion is understood quite well.
 


Because we can only model it in 1D.
 


although said model works fairly well in 3D scenarios.
 


Kracatoan said:
Because we can only model it in 1D.

This is simply not true, there is problem with 3d models.
 

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