What is the change in entropy for a colloid settling out of solution?

In summary, sedimentation occurs due to an external force, such as gravity, which is not a closed and insulated system. This causes frictional heating in the liquid and increases the total entropy. In an isolated system, other mechanisms, such as entropy-driven phase transitions and self-assembly, can also contribute to increasing entropy.
  • #1
Timtam
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If it occurs spontaneously then it must increase entropy but the possible micro states reduce so what else is occurring to increase entropy
 
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  • #2
Let's assume a closed system.

I think you have to ask yourself: why were the colloids originally suspended? I think because the fluid was agitated. The fluid then settles down, and the colloids then settle out of suspension. Where did that KE of the fluid go to? (...and the PE of the colloids.) It raised the temperature of your system, so now the water molecules have more accessible microstates.
 
  • #3
Timtam said:
If it occurs spontaneously then it must increase entropy...
A closed system which isn‘t in an equilibrium state “evolves” in such a way to minimize – depending on the constraints – its Gibbs or Helmholtz free energy.
 
  • #4
Timtam said:
Summary:: If it occurs spontaneously then it must increase entropy but the possible micro states reduce so what else is occurring to increase entropy

If it occurs spontaneously then it must increase entropy but the possible micro states reduce so what else is occurring to increase entropy

Settling occurs because of gravity- an external force- the colloid system is not closed. Take away gravity and while sedimentation no longer occurs, phase separations can occur by other mechanisms- an interesting one is entropy-driven phase transitions and self-assembly:

https://arxiv.org/abs/cond-mat/0402585
https://www.physics.upenn.edu/yodhlab/docs/yodh_Phys295_Entropic_Forces.pdf
 
  • #5
Andy Resnick said:
Settling occurs because of gravity- an external force- the colloid system is not closed.
Your comment made me realize that I should have said closed and insulated. I believe you are trying to say the system is not isolated.
 
  • #6
When the colloid particles settle on the bottom of the container, their motion causes frictional heating in the liquid. This increases the total entropy.
 
  • #7

Related to What is the change in entropy for a colloid settling out of solution?

1. What is entropy?

Entropy is a measure of the disorder or randomness in a system. It is a thermodynamic quantity that describes the distribution of energy in a system.

2. How is entropy related to the settling of a colloid out of solution?

The settling of a colloid out of solution involves a decrease in entropy. This is because the particles in a colloid are dispersed and randomly distributed in the solution, but when they settle, they become more ordered and less random, resulting in a decrease in entropy.

3. What factors affect the change in entropy for a colloid settling out of solution?

The change in entropy for a colloid settling out of solution is affected by the size and shape of the particles, the concentration of the colloid, and the temperature of the solution. In general, smaller particles, higher concentrations, and lower temperatures result in a larger decrease in entropy.

4. How is the change in entropy for a colloid settling out of solution calculated?

The change in entropy for a colloid settling out of solution can be calculated using the equation ΔS = k ln(Wf/Wi), where k is the Boltzmann constant, Wf is the final number of microstates (arrangements) of the particles after settling, and Wi is the initial number of microstates of the particles in solution.

5. Can the change in entropy for a colloid settling out of solution be reversed?

Yes, the change in entropy for a colloid settling out of solution can be reversed by adding energy to the system. This can be achieved by heating the solution, which will increase the randomness and disorder of the particles, resulting in an increase in entropy.

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