Why does hot water freeze quicker than cold

Discussion in 'Plumbers' Talk' started by Lokkars Daisy, Jul 13, 2012.

  1. Lokkars Daisy

    Lokkars Daisy New Member

    Can you water heads please tell me why if a place two jugs of water in my freezer, one containing water at 30 deg C and tother at 100 deg C  It is the 100 deg jug of water that freezes first ?
     
  2. Mr. Handyandy

    Mr. Handyandy Screwfix Select

    Maybe because it's less dense.

    Mr. HandyAndy - Really
     
  3. Lokkars Daisy

    Lokkars Daisy New Member

    You could be right Handy , an you would get a Noble prize
     
  4. proff

    proff New Member

    The bigger the Temperature Difference the bigger the Heat Transfer, in other words it's Magic. ;)
     
  5. joinerjohn1

    joinerjohn1 Screwfix Select

    It's called the  Mpemba Effect after a Tanzanian student who noticed the effect when he was in his 3rd year at secondary school. Various hypotheses have been put forward as the explanation. Some think it's due to the evaporation of the hotter liquid. Others think that frost forms on the outside of the cooler container and insulates the cooler liquid. Another explanation is that the hotter liquid allows convection currents to carry colder liquid.
    There is a prize of £1000 up for grabs by the first person to fully explain the Mpemba effect, offered by the Royal Society of Chemistry. So get working on your pet theory lads. ;)
     
  6. tom.plum

    tom.plum Screwfix Select

    andrews guess is the right answer, water varies in density according to the temperature, at 4 degree's C water is at its most dence and is called 'heavy water', if you cool it it becomes less dence on a rising scale untill it reaches 0 degrees at which it forms ice, if you heat it from 4 degrees it also becomes less dence at a rising scale till it reaches 100 derees C and it becomes steam,
    so your jug of steam is a lot less dence than the other jug of luke warm, and freezes quicker,
     
  7. Crowsfoot

    Crowsfoot Screwfix Select

    Actually, it's because hot water contains less minerals than cold water.
    When water is heated/boiled it gives up it's minerals which in turn causes it to freeze quicker than cold water (which still has more minerals in it).
    And I should know because I've got an FTC in building Science.
     
  8. sam spade

    sam spade Active Member

    Water is unique in that its density "peaks" at a temperature of 4degC. It reduces as the temperature increases above 4C and as the temperature reduces below 4C. But that is not "heavy water". HW is something completely different.

    A normal water molecule consists of two atoms of Hydrogen and one of Oxygen - H?O. In "Heavy water" the Hydrogen is replaced by a different isotope of Hydrogen , called Deuterium (D or ²H), so "heavy water" is D?O or ²H?O.
     
  9. sam spade

    sam spade Active Member

    Then you should hurry up and claim the £1000 prize.
     
  10. tom.plum

    tom.plum Screwfix Select

    ok, I'll try again, are both jugs on the same shelf ? because heat rises, unless its in a duck pond, in a duck pond the ice forms at the top, therefore the 'warmer water' must be on the bottom and therefore not rising, So if the jug with the steam in is on the top shelf, thats why it freezes faster,
    where's me grand?
     
  11. Crowsfoot might be on to something...

    Water requires solid particles to be present before it can freeze - absolutely pure water won't freeze. So perhaps the heated water freezes more quickly because heating it takes the disolved minerals out of solution and they form lost of wee particles for the ice crystals to form on?

    Begs 2 questions: (1) has this experiment been done - as it should of  - with distilled water? And (2) is Lokks talking barlocks in the first place...?
     
  12. chippie244

    chippie244 Super Member

    Isn't it something to do with the latent heat of evaporation, the same reason it gets warmer when it snows?
     
  13. Mr. Handyandy

    Mr. Handyandy Screwfix Select

    But boiled water will have some impurities 'boiled out'!

    Water used for babies is boiled then cooled for this reason.

    Mr. HandyAndy - Really
     
  14. Mr. Handyandy

    Mr. Handyandy Screwfix Select

    Frost is formed quicker than ice yet has the same freezing temperature!

    Frost is the freezing of miniature particles of water(dew). ie many times less dense per area.(see dew as very far expanded water)

    Also, hot water will be less robust having been boiled.

    Mr. HandyAndy - Really
     
  15. Crowsfoot

    Crowsfoot Screwfix Select

    We're all getting a bit mixed up here.

    Sure cold water is more dense than hot water but that's not the reason why it freezes more quickly.

    Hot water won't freeze; it must be "Zero" before any water will freeze hot or cold!
    Have a look in the bottom of your kettle and you will see the tiny minerals that have been removed by the process of boiling up water.
    This water will freeze more quickly than cold water that hasn't been heated because there is now less mineral content in it.


    Anyone know why hot water won't freeze?
    It's quite a "simple science" answer!
    Hot water won't freeze because it's  - - - - - -
     
  16. sam spade

    sam spade Active Member

    Where did you get that idea from?
     
  17. tom.plum

    tom.plum Screwfix Select

    devs got mixed up with, pure alcohol won't freeze, its easy done, I do it all the time
     
  18. Water Systems

    Water Systems New Member

    Heat does not rise. It conducts.  Hot water rises. Hot air rises.  Why? because hot water is less dense than colder water and hot air is less dense than cold air..
     
  19. joinerjohn1

    joinerjohn1 Screwfix Select

    Heat does not conduct. Materials like metal, water etc conduct heat, but heat itself doesn't conduct. It might radiate though.
     

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