1. Limited time only! Sign up for a free 30min personal tutor trial with Chegg Tutors
    Dismiss Notice
Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Homework Help: 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


    User Avatar

    Staff: Mentor

    How is it related to the volume of liquid?
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook