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Quantity of heat absorbed or released

  1. Mar 27, 2008 #1
    1. The problem statement, all variables and given/known data

    Calculate the quantity of heat absorbed (+) or released (-) during each of these changes: A. 250g. of water (about 1 cup)is heated from 15 degrees centigrade to 100 degrees; B. 500g. of water is cooled from 95 degrees centigrade to 55 degrees; C. 5.0ml. of water at 4 degrees centigrade is warmed to 44 degrees centigrade. Be sure to show all your calculation work in each case.

    2. Relevant equations

    My book gave me the formula 1.00 cal/g x C (with the degrees “dot,” – don’t know how to insert it in typing). It said that this means 1 cal will raise the temp of 1 gram of water by 1 degree. The book also gave another forumla to use 4.18J/g x C (again degrees)

    3. The attempt at a solution

    Which formula should I use for this question? I realized that an increase in temp = absobed heat and decrease in temp = released heat, so A and C would be absorbed heat and B released heat. Also, when the question uses centigrade, is it ok to think of it as Celsius? I read that they are pretty interchangable, but I want to make sure it isn't a "trick" question.

    A. 1.00 cal / 250g x C (temp.) Is the temp the 15, 100 or the difference between the two (85).
    B. 1.00 cal / 500g x C (temp) Is the temp the 95, 55 or the difference of 40?
    C. Since this one is in mL, I am a little uncertain if this formula still applies as it is in grams. Or do I need to do some converting?

    I am under the impression that quantity of heat thing has some thing to do with Joules. So should my answer be in Joules?:confused:
     
  2. jcsd
  3. Mar 27, 2008 #2
    the AMOUNT OF ENERGY required to raise the temperature (or released to cool the temperature) depends on what? there are actually 3 parameters.

    calories and joules are different units for energy. ignore the calories in this question, interprete it as being joules unless the answer required is to be in joules, then you need to convert cal to J.

    Hint: density of water is taken as 1 g/cm3 or 1 g/ml
    so, what can you deduce?
     
    Last edited: Mar 27, 2008
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