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Why does water volume increase when heated?

  1. Mar 24, 2009 #1
    1. The problem statement, all variables and given/known data
    Why does water volume increase when heated past 4 degrees Celsius?

    2. The attempt at a solution
    I know that water molecules move quicker when energy is applied (e.g. heat), but I don't understand why the volume of water must increase. Why can't water molecules just move quicker in the same amount of space? I need a molecular explanation. Thanks!
     
  2. jcsd
  3. Mar 25, 2009 #2
    Hello, and welcome to PF.

    A simple thought experiment may help to clarify this for you. Consider a group of people standing shoulder-to-shoulder and the floor area they occupy. Now, give them sugar (energy) and have them dance to fast-tempo music (~boiling). Consider the floor area they would then occupy.
     
  4. Mar 26, 2009 #3

    Charles's law - related to the gas laws, and the Ideal gas law (PV=nRT), explains that

    [tex]\frac{V_{1}}{T_{1}} = constant} [/tex] or V[tex]_{1}=T_{1}[/tex]
    Why gases expand:
    When temperature goes up, so does volume.

    Why all states of matter expand with energy:
    When energy is added, the particles move faster and bounce off the container harder. The average kinetic energy of each molecule increases as the temperature goes up. As a result, the particles move away from each other, causing the volume to increase.

    EDIT: :bugeye: Somehow I missed that the question was about liquid water. Sorry.....
    Charles's law is not related to liquids...thanks Borek.
     
    Last edited: Mar 26, 2009
  5. Mar 26, 2009 #4

    Borek

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    Staff: Mentor

    How is it related to the volume of liquid?
     
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