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B My Third Post: Change of Intermolecular Distance?

  1. Aug 1, 2018 #1
    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
     
  2. jcsd
  3. Aug 1, 2018 #2
    In each case, what do you think it will happens when the external forces are suppressed?
     
  4. Aug 1, 2018 #3

    Dale

    Staff: Mentor

    This is basically just Hookes law, which we have discussed previously
     
  5. Aug 4, 2018 #4
    Is there a generalized formula for the distance between two molecules in the case where no forces are being applied at all?
     
  6. Aug 4, 2018 #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.
     
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