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Heat of fusion question

  1. Oct 7, 2016 #1
    So i did a lab were we melt an ice cube in water. So i have to find the heat of fusion for the ice cube. But i am not sure how to do that.

    What i was thinking of doing is finding the energy released by temperature of the ice cube increasing, then make that value of q, equal to m*hf, when it is melting. So:

    Q = m * hf

    Q/ m = hf

    would this be correct? if you want my data it is:

    mass of ice cube = 22.82 g

    temperature = -7 degrees celcius

    and for specific heat capacity i used 2.10 joules/ gram * degrees celcius

    i know the theoretical value is 333, but my teacher is saying that our value of hf needs to be different.
     
  2. jcsd
  3. Oct 7, 2016 #2

    Borek

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    Staff: Mentor

    Please describe the experiment, so far there is not enough information to help you (I guess I know what you did, and if so what you suggested is wrong, but I prefer to be sure).

    Can you describe - step by step - changes that occurred to the ice cube during the experiment? Where did the heat needed for these changes came from?
     
  4. Oct 7, 2016 #3
    so this is how the experiment went:

    we took a styrofoam cup , weighed it, added water into the cup and weighed it again. We then recorded the temperature of the war which was 23 degrees celcius. We then put an ice cube into the styrofoam cup with the water and waited for it to melt, we then recorded the temperature of the water and melted ice cube and got 9 degrees celcius, we weighed the mass again. After our teacher told us that the temperature of the ice cube was 7 degrees celcius.


    Mass of Styrofoam cup = 3.56 g

    Mass of Styrofoam cup + water = 145.78 g

    Mass of Styrofoam cup + water + melted ice cube = 168.6 g

    T1 = 23°c

    T2 = 9° c

    Tice = -7°c
     
  5. Oct 7, 2016 #4

    Borek

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    Staff: Mentor

    I hate to ask teh same question again and again, but sometimes I have no choice.

     
  6. Oct 16, 2016 #5

    James Pelezo

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    Gold Member

    Start with listing the events having heat transfer history and apply the law of conservation of energy to the sum of the thermal events. I suggest looking up and reviewing solving 'method of mixtures' type problems in closed systems. These studies are also called 'Coffee Cup Calorimeter type experiments. Thermodynamics sections of most college chemistry or physics texts have some great examples.
     
  7. Oct 25, 2016 #6
    Don't forget to determine the heat capacity of the styrofoam cups.
     
  8. Oct 26, 2016 #7

    James Pelezo

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    Gold Member

    Interesting proposition... but how do you measure the temperature change of the styrofoam cup? I would think it would be negligible compared to ΔT for water, but I'm always open to technique.
     
  9. Oct 26, 2016 #8
    I think what you mean is that the heat transferred to or from the styrofoam cup is negligible compared to the other heat effects in this system.
     
  10. Oct 26, 2016 #9

    James Pelezo

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    Gold Member

    Yes, Chet ... much better said. Thanks.
     
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