Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Maximum density

  1. Apr 2, 2006 #1
    i have had this problem for some time. why exactly does water show a maximum density at about 277 K. and is it the only substance to show such a behaviour.
  2. jcsd
  3. Apr 2, 2006 #2
    From http://www.simetric.co.uk/si_water.htm

    "When water freezes it expands rapidly adding about 9 % by volume. Fresh water has a maximum density at around 4° Celsius. Water is the only substance where the maximum density does not occur when solidified. As ice is lighter than water, it floats."
    Now, I can not speak for the accuracy of that statement, but that's what that link says.
  4. Apr 2, 2006 #3
    The reason for water's remarkable properties are usually traceable to the fact that it is such a polar molecule. I would imagine that other polar molecular substances might have similar properties. It would be a place to start looking, anyway.

  5. Apr 3, 2006 #4

    Meir Achuz

    User Avatar
    Science Advisor
    Homework Helper
    Gold Member

    If that were not true, we couldn't go ice fishing.
  6. Apr 3, 2006 #5


    User Avatar

    Staff: Mentor

    ?? That is true - the max density is at 4C (277K) and it decreases from there, which makes ice float. That's also what keeps lakes from freezing solid: 4C water being the least dense, sets up a convection, circulating ground heat.

    My understanding was that the crystal structure(s) is unique in being less dense than the liquid state and below 4C, the molecules start to line-up, decreasing the density.
    Last edited: Apr 3, 2006
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook