My Third Post: Change of Intermolecular Distance?

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Discussion Overview

The discussion revolves around the behavior of intermolecular forces in a rod made of two identical molecules when external forces are applied. It explores concepts from physics and chemistry, particularly in relation to equilibrium, intermolecular distances, and the Lennard-Jones model.

Discussion Character

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

Main Points Raised

  • One participant describes a scenario where two molecules, A and B, are pulled in opposite directions, suggesting that attractive intermolecular forces will act to maintain equilibrium, consistent with the Lennard-Jones model.
  • Another participant questions what happens to the system when the external forces are removed, implying a need for further exploration of the system's behavior.
  • A participant asserts that the situation can be understood through Hooke's law, indicating a connection to elastic behavior.
  • There is a request for a generalized formula for the distance between two molecules when no external forces are applied, indicating a search for a theoretical framework.
  • One participant raises a distinction between physics and chemistry in the context of intermolecular forces, suggesting that the discussion may straddle both fields.

Areas of Agreement / Disagreement

Participants express differing views on the nature of the forces involved and the relevance of the discussion to physics versus chemistry. There is no consensus on the implications of the external forces or the appropriate theoretical framework to apply.

Contextual Notes

The discussion does not resolve the assumptions regarding the nature of intermolecular forces or the applicability of Hooke's law in this context. There is also ambiguity regarding the definitions of terms used, particularly in relation to physics and chemistry.

Who May Find This Useful

This discussion may be of interest to those studying molecular physics, chemistry, or anyone exploring the interactions between forces and molecular behavior.

Weam Abou Hamdan
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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
 
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In each case, what do you think it will happens when the external forces are suppressed?
 
This is basically just Hookes law, which we have discussed previously
 
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?
 
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.
 

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