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

In summary, the reason why a less dense liquid "floats" on top of a more dense liquid is due to the principle of potential energy. When two liquids with different densities are mixed, they will separate into layers based on the strength of their intermolecular forces. If the forces between the two liquids are close in value to the forces within each liquid, they will dissolve nicely without the need for a chemical reaction. This process is known as solvation and can be further studied in a Chemistry course.
  • #1
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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  • #2
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?
 
  • #3
Sorry. Yes. This is my question,
 
  • #4
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.
 
  • #5
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?
 
  • #6
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.
 
  • #7
So, the intermolecular forces must not be bigger than forces between same moleculas of liguid? Only must be the two different molecules close?
 
  • #8
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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  • #9
Ok, thank you very much :-)
 

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

1. What is the concept of density in molecular physics?

Density is a measure of how much mass is contained in a given volume. In molecular physics, it refers to the number of molecules present in a certain amount of space.

2. How does molecular structure affect density?

The arrangement of molecules in a substance can affect its density. In general, substances with tightly packed molecules will have a higher density, while those with loosely packed molecules will have a lower density.

3. Why is a less dense liquid higher than a more dense liquid?

This is because of the phenomenon known as buoyancy. When a less dense liquid is placed on top of a more dense liquid, the less dense liquid will float because it is less affected by gravity.

4. Can density be changed in a substance?

Yes, density can be changed by altering the temperature and pressure of a substance. As temperature and pressure increase, the molecules in a substance become more compressed, leading to a higher density.

5. How is density used in understanding the behavior of liquids?

Density is an important factor in understanding the properties and behavior of liquids. It can help us predict how a liquid will interact with other substances and how it will behave under different conditions.

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