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B Energy release from 75c drop in water temp, 1L?

  1. Oct 13, 2016 #1
    Hey everyone can anyone tell me how much energy is released (joules) if you take 1 liter of water at 100C and drop it down to 25C (room temp, reg pressure)? Is it significant amount?

    Better even how much energy is released (approximately) for every 1c drop in temp? Is the release in energy linear? Say 90C to 89C vs 50C to 49C, both same amount of energy?
     
    Last edited: Oct 14, 2016
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  3. Oct 13, 2016 #2

    Simon Bridge

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    Most people here can, but you will benifit more by working it out for yourself.
    http://hyperphysics.phy-astr.gsu.edu/hbase/thermo/spht.html
    ... answers all your questions.
    Dunno - what do you mean by "significant"?

    Niggle:
    You mean, 1 litre of water at 100C drop to 25C?
    A "1 litter" is "one platform for carrying people on", and "100c" is a dollar.
     
  4. Oct 14, 2016 #3
    Lol. So it basically: 80C x 800g x 4.2J= 268,800J? Or am I not doing this right?

    Seeing how a AA battery only has about 10,000J, I would consider that significant ;-). In fact I'm kind of shocked it would take about 27 AA batteries
     
  5. Oct 14, 2016 #4

    Simon Bridge

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    That's right - this is why water plays such a big role in temperature regulation. Though it takes 27 AA batteries to heat the water ... it cools down all by itself.

    You can check that it makes sense by considering how long it takes for your kettle to bring a cup of water to boil.
     
  6. Oct 14, 2016 #5
    Yea this is true. Is the heating and cooling linear? What I mean is does it take same amount to go from 20 to 21C and it does to go for 90 to 91C for example?
     
  7. Oct 14, 2016 #6

    Simon Bridge

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    In terms of the link I gave you, this question amounts to asking if the specific heat is a constant with temperature... for the temperature ranges you cite, for water, yes. However, this is not generally the case, which is why tables of specific heats also list the temperature where they were measured.

    Then there is the case of phase changes - look up "latent heat".
     
  8. Oct 14, 2016 #7
    Will do and thanks.
     
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