Molecular Physics: Why is Less Dense Liquid Higher Than More Dense?

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Discussion Overview

The discussion revolves around the molecular physics concepts explaining why a less dense liquid floats on a more dense liquid, as well as the conditions under which two liquids can mix. Participants explore the underlying forces and potential energy considerations involved in these phenomena.

Discussion Character

  • Exploratory
  • Technical explanation
  • Conceptual clarification
  • Debate/contested

Main Points Raised

  • Some participants propose that the concept of potential energy is key to understanding why less dense liquids float on more dense liquids, suggesting that liquids seek the lowest potential energy configuration.
  • Others argue that the intermolecular forces between different liquids must be comparable to the forces within the same liquid for them to mix, without necessarily requiring a chemical reaction.
  • A later reply questions whether the intermolecular forces between different liquids need to be stronger than those within the same liquid for mixing to occur.
  • Participants discuss the role of molecular attraction, particularly noting that stronger attractions between like molecules (e.g., water) can lead to separation from other liquids (e.g., oil).

Areas of Agreement / Disagreement

Participants generally agree on the role of potential energy and intermolecular forces in explaining the behavior of liquids, but there is no consensus on the specifics of how these forces interact or the necessity of chemical reactions for mixing.

Contextual Notes

Limitations include the lack of clarity on the definitions of intermolecular forces and potential energy in this context, as well as the unresolved nature of how these forces influence the behavior of different liquids.

Who May Find This Useful

This discussion may be useful for individuals interested in molecular physics, chemistry, and the behavior of liquids, particularly in understanding the principles of density and mixing.

Oomph!
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Please, tell me really simply from the viewpoint of molecular physics... Why is liquid having a smaller density on liquid having a bigger density? Thanks
 
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Oomph! said:
Please, tell me really simply from the viewpoint of molecular physics... Why is liquid having a smaller density on liquid having a bigger density? Thanks

Your question did not translate very well -- are you asking why a less dense liquid "floats" on top of a more dense liquid?
 
Sorry. Yes. This is my question,
 
berkeman said:
Your question did not translate very well -- are you asking why a less dense liquid "floats" on top of a more dense liquid?

For this question (expertly found by Berkeman) there is no need for Molecular physics just Archimedes.
If you place 2 different density liquids with a vertical separator and then remove the separator liquids will search the lowest potential energy position. So the heavy liquids bottom position will be lower in potential energy than the vice-versa. it is not as the lighter liquid does not seek it's lower potential energy position, it is just that it's potential energy is lower.

For some reason I think you are trying to ask why two liquids separate into a boundary. As a fine mixture of oil and water (can be done and it will settle into oil above and water below). It is just because the Water molecules attract each other much stronger that Water molecules attract oil molecules. So the water molecules seek their respective most stable configuration (again with the potential energy - although Molecular Physics) and gather into a big clump leaving the oil to clump with it self. Then you get the above situation where the heavy and light clumps go into the configuration with the lowest potential energy.
 
Ok, thank you very much. However, if some liquid has bigger density and some liquid had lower density, they can be mixed, if is the force between molecule of liquid with lower density and molecule of liquid od bigger density stronger than force of same molecules. It is right? Must occur chemical reaction?
 
Oomph! said:
Ok, thank you very much. However, if some liquid has bigger density and some liquid had lower density, they can be mixed, if is the force between molecule of liquid with lower density and molecule of liquid od bigger density stronger than force of same molecules. It is right? Must occur chemical reaction?

A chemical reaction is not needed to occur.

For two liquids to dissolve, it is necessary for the intermolecular forces to be close irrespective of their density.
 
So, the intermolecular forces must not be bigger than forces between same moleculas of liguid? Only must be the two different molecules close?
 
Too put it simply.

The intermolecular forces (liquid 1 with liquid 2) must be close in value to the intermolecular force of liquid 1 with liquid 1.
Example:
Liquid1-Liquid1 - strong force ... Liquid2 -Liquid2 weak force
If Liquid1-Liquid2 is close in strength to Liquid1-Liquid1 they will dissolve nicely. In this case Liquid2 -Liquid2 force does not contribute to their solvation.

For a more detailed picture you can look up solvation in a Chemistry Introductory Course or Book.
 
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Ok, thank you very much :-)
 

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