My Third Post: Change of Intermolecular Distance?

In summary, the conversation discussed the concept of equilibrium in a rod composed of two identical molecules, A and B. It was mentioned that when equal external forces are applied in opposite directions, an attractive intermolecular force is exerted between A and B to maintain equilibrium. This is consistent with the Lennard-Jones model, which explains the intermolecular force as being attractive when the distance between molecules exceeds the equilibrium distance. The same result is observed when the forces are directed inwards. However, when no external forces are applied, the distance between the molecules follows Hookes law and is dependent on the van der Waals forces, which are very weak interactions between atoms or molecules. The applicability of this concept depends on whether the question
  • #1
Weam Abou Hamdan
25
3
Hello,

Let us imagine a rod resting on a frictionless horizontal surface such that the rod is made up of 2 identical molecules. Let these molecules be named A and B from left to right. If we pull A to the left and B to the right with forces of equal magnitude, the rod must remain at equilibrium according to Newton's First Law of Motion. This means that A and B must remain at equilibrium as well. Then, when A and B are pulled in opposite directions, an attractive intermolecular force will be exerted between A and B to cancel out the externally applied forces. This is consistent with the Lennard-Jones model since the intermolecular force was attractive when the distance between the molecules exceeded the equilibrium distance. The rod remains at equilibrium, but it becomes larger in length after the outward forces are applied.

A similar result would be obtained if the forces were directed inwards instead. In this case, the intermolecular force would be repulsive to cancel out the externally applied forces. Also, it would be consistent with the Lennard-Jones model since the distance between the molecules became less than the equilibrium distance. The rod remains at equilibrium, but it becomes shorter in length after the inward forces are applied.

Is this true?

Weam Abou Hamdan
Thursday, August 2, 2018
 
Physics news on Phys.org
  • #2
In each case, what do you think it will happens when the external forces are suppressed?
 
  • #3
This is basically just Hookes law, which we have discussed previously
 
  • #4
Dale said:
This is basically just Hookes law, which we have discussed previously
Is there a generalized formula for the distance between two molecules in the case where no forces are being applied at all?
 
  • #5
Your question is about Physics or is about Chemistry?
In molecular physics the van der Waals forces, named after Dutch scientist Johannes Diderik van der Waals, are distance-dependent and very week interactions between atoms or molecules.
If your question is about Physics, Dale post is OK.
If your question is about Chemistry, you must give more detail.
 

1. How does the change in intermolecular distance affect the physical properties of a substance?

The change in intermolecular distance can affect the physical properties of a substance in various ways. For example, if the intermolecular distance increases, the substance may become less dense and have a lower boiling point. On the other hand, a decrease in intermolecular distance can lead to a higher density and a higher boiling point. Additionally, changes in intermolecular distance can also affect the substance's viscosity, surface tension, and thermal conductivity.

2. What factors can cause a change in intermolecular distance?

There are several factors that can cause a change in intermolecular distance. These include temperature, pressure, and the presence of other substances. For instance, an increase in temperature can cause molecules to move faster and increase the distance between them. Similarly, an increase in pressure can push molecules closer together, resulting in a decrease in intermolecular distance. The presence of other substances, such as solvents or additives, can also affect the intermolecular distance by altering the interactions between molecules.

3. How does the change in intermolecular distance impact the strength of intermolecular forces?

The change in intermolecular distance can directly affect the strength of intermolecular forces. As the distance between molecules increases, the strength of these forces decreases. This is because the attractive forces between molecules, such as dipole-dipole interactions or hydrogen bonding, become weaker as the distance between them increases. On the other hand, a decrease in intermolecular distance can strengthen these forces, making it more difficult for molecules to separate from each other.

4. Can changes in intermolecular distance lead to phase changes?

Yes, changes in intermolecular distance can lead to phase changes in a substance. For example, if the intermolecular distance between molecules decreases, it can cause the substance to change from a gas to a liquid or from a liquid to a solid. This is because the intermolecular forces become stronger, making it easier for molecules to stick together and form a more structured phase. Similarly, an increase in intermolecular distance can cause a substance to change from a solid to a liquid or from a liquid to a gas.

5. How can we measure changes in intermolecular distance?

There are several methods for measuring changes in intermolecular distance, depending on the type of substance and the specific distance being measured. For example, spectroscopy techniques can be used to measure changes in the distance between atoms in a molecule. Other techniques, such as X-ray diffraction or scanning probe microscopy, can be used to measure changes in intermolecular distance in a solid or liquid state. Additionally, changes in intermolecular distance can also be indirectly measured by observing changes in physical properties, such as density or boiling point, as mentioned earlier.

Similar threads

  • Atomic and Condensed Matter
Replies
4
Views
1K
  • Atomic and Condensed Matter
Replies
1
Views
1K
Replies
28
Views
2K
Replies
22
Views
2K
  • Introductory Physics Homework Help
Replies
15
Views
6K
  • Introductory Physics Homework Help
Replies
15
Views
2K
  • Other Physics Topics
Replies
1
Views
1K
Replies
1
Views
4K
  • Atomic and Condensed Matter
Replies
2
Views
3K
  • Introductory Physics Homework Help
Replies
9
Views
1K
Back
Top