Why convection happens when concentration gradients exist?

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SUMMARY

The discussion centers on the phenomenon of convection occurring under concentration gradients, specifically in a closed container divided into two sections. When one section contains a million particles and the other none, diffusion leads to an equal distribution of particles over time, illustrating the principle of entropy increase. The participants agree that the driving force behind this uniform distribution is statistical in nature, rather than a specific force acting on the particles. The explanation provided clarifies that the movement of particles is a result of diffusive flow due to concentration differences.

PREREQUISITES
  • Understanding of basic thermodynamics principles, particularly entropy.
  • Familiarity with particle diffusion concepts.
  • Knowledge of statistical mechanics and its application to particle behavior.
  • Basic grasp of closed system dynamics in physics.
NEXT STEPS
  • Research the laws of thermodynamics, focusing on entropy and its implications.
  • Study diffusion processes in gases and liquids, including Fick's laws.
  • Explore statistical mechanics to understand particle distribution in closed systems.
  • Investigate real-world applications of convection and diffusion in various scientific fields.
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Students of physics, researchers in thermodynamics, and anyone interested in the principles of particle behavior and statistical mechanics will benefit from this discussion.

lionelwang
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Hello, everyone!

I could not imagine what force makes this convection under concentration gradients , no matter how hard I thought.
Maybe we can use principle of entropy increase to explain it, but that is not vivid to me.

anyone can help me? Thans!
 
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Consider a closed container which we mentally divide into two equally shaped and sized sections, denoted the left and right sections.

If at zero time there are a million particles in the left side, and no particles in the right, and all these particles are bouncing around randomly, how many particles would you expect to end up in each section if we wait long enough for the average number of particles in each to be constant?

Naturally half will end up in each section. So during the waiting period, half the particles moved to the right, due to the concentration difference. This is the diffussive flow, which as you suggest is due to the entropy increase. There is only one way to have all particles in the left compartment but very many ways to have half the particles in each compartment.
 
Thank you for your explanation! It is vey clear and easy to understand, maybe it is a problem of statistics as you explained, the force which result in the uniform distribution of the molecules is not important.



jVincent said:
Consider a closed container which we mentally divide into two equally shaped and sized sections, denoted the left and right sections.

If at zero time there are a million particles in the left side, and no particles in the right, and all these particles are bouncing around randomly, how many particles would you expect to end up in each section if we wait long enough for the average number of particles in each to be constant?

Naturally half will end up in each section. So during the waiting period, half the particles moved to the right, due to the concentration difference. This is the diffussive flow, which as you suggest is due to the entropy increase. There is only one way to have all particles in the left compartment but very many ways to have half the particles in each compartment.
 

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