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Homework Help: Calorimetry problem and temperature

  1. Apr 6, 2010 #1
    1. The problem statement, all variables and given/known data
    A student attempts to identify a metal by measuring its specific heat capacity. 100g of the metal is heated to 75°C and then transferred to a 70g copper calorimeter containing 200g of water at 20°C. The temperature of the final mixture is 25°C.

    2. Relevant equations

    heat lost by sample = heat gained by water

    3. The attempt at a solution
    Given metal: Given water:
    m = .1kg m = .2kg
    c = ? c = 4.2e3 J/kg°C
    t1 = 75°C t1 = 20°C
    t2 = 25°C t2 = 25°C
    c = - [.2kg * 4.2e3 J/kg°C]/ *25°C - 20°C/
    .1kg 25°C - 75°C
    = 840 J/kg°C
    ok well..this is wrong...does the fact that the calorimeter is 70g copper affect the answer
  2. jcsd
  3. Apr 6, 2010 #2
    Do you how much heat is needed to change the temperature of 1 kg of water by 1 degree Celsius. It is 4186 Joule. So How much heat is needed to change the temperature of 200 g of water by 1 degree Celsius ? It is 5 time less heat than 1 Kg of water. But you have changed the temperature of water by 5 degree Celsius. So total heat needed to change the temperature of 200 g of water by 5 degree Celsius is:

    (4186 * 5)/5

    = 4186 Joule.

    Now copper also needed some heat to raise its temperature by 5 degree Celsius.

    We need 387 Joule of heat to raise the temperature of 1 kg of copper by 1 degree Celsius.

    So to raise the temperature of 70 g copper by 5 degree Celsius is ................???

    Now add both the heat and find what is the total heat lost by the metal and due to this lost how much is the change in the temperature. From there you can find its specific heat.
  4. Apr 6, 2010 #3
    It may be nearly equal to 864.29 J/kg per degree Celsius. Is I'm right? I'm not very good with Physics so I apologize if I've mislead you on any step.
  5. Apr 6, 2010 #4
    -so copper's heat gained is (387J *5)/14 =138J....so the heat gained by both is 4324J...so that's the heat lost by the sample, so the sample's specific heat capacity is...864J/Kg*C...but that's no the right answer..b/c the choices i have to choose from for the answer are 4200J/Kg*K, 900J/Kg * K, 440J/kg *, 390, 370, 130....
  6. Apr 6, 2010 #5
    Tell the correct answer. Is it 900 J/ kg *K. Is it Aluminum.
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