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What are the attractive forces in a neutral fluid?

  1. Jul 12, 2015 #1
    Hi!

    I wonder about how for instance water temperature is changed with regard to applied heat.

    You all know that if you take ice and heat it up temperture will climb until it reaches 0C.

    When it reaches 0C it however stobs climbing in tempertaure regardless of how much heat you supply.

    It is said that heat is needed to overcome the attractive forces of the molecules instead of just giving them higher speed (i.e Ek and thus temperature).

    It is said that these attractive forces constitute a potential energy to be overcome before the molecules can move faster thus giving the fluid higher temperature, Ek.

    I just wonder what these attractive forces are because as far I understand there is no attractive forces between neutral molecules.

    And regardless of state (solid, liquid or vapour) neutral H20 is still the molecule in mind.

    So where is the attractive forces?

    Best regards, Roger
     
  2. jcsd
  3. Jul 12, 2015 #2

    jtbell

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    Staff: Mentor

    Look up "van der Waals forces".
     
  4. Jul 12, 2015 #3
    Van der Waal considers both the physical size of gas particles and "intermolecular attractions".

    I have read this fantastic site: http://www.et.byu.edu/~rowley/ChEn2...e_Systems/Van_der_Waals_Equation_of_State.htm

    And it states that there are "intermolecular attractions".

    But it never explains how or why.

    So my question remains, how can there be intermolecular attractions between neutral molecules?

    Best regards, Roger
     
  5. Jul 12, 2015 #4
    Another thing, I am interested in all the states of matter.

    Van der Waal only considers the gas state.

    Best regards, Roger
     
  6. Jul 12, 2015 #5
    I can't answer in general, but at least water is a polar molecule. Taken as a whole it is neutral, but it isn't made of neutral particles. Since the particles are separated, it has a dipole electric field. I forget a kot of chem, but I bet a lot of intermolecular forces are electric forces due to uneven electon sharing.
     
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