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Homework Help: Mass of N loss

  1. Mar 24, 2008 #1


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    [SOLVED] Mass of N loss

    1. The problem statement, all variables and given/known data
    1.00kg block of Cu at 20C is dropped into a large vessel of liq Nitrogen at 77.3K. How many kg of Nitrogen boil away by the time the copper reaches 77.3K?
    specific heat of Cu is 0.0920cal/g C. The latent heat of vaporization of Nitrogen is 48.0cal/g

    2. Relevant equations
    [tex]Q= mc\Delta T[/tex]
    [tex]Q= \pm mL[/tex]
    [tex] Q_{cold}= -Q_{hot} [/tex]
    3. The attempt at a solution

    I'm not sure how to do this problem but I know what equations are needed.
    L= 48.0cal/g
    [tex]M_{cu}= 1.00kg[/tex]
    [tex]M_{N}= ? [/tex]
    [tex]T_f= 77.3K= -195.85^oC [/tex]
    [tex]T_i= 20^oC[/tex]

    Do I just solve for mass of the Nitrogen after I equate the 2 energy equations together?
    like this:
    [tex]- M_{Cu}C_{Cu}\Delta T= M_{Nitrogen}L[/tex]

    Help please.

    Thank You
    Last edited: Mar 24, 2008
  2. jcsd
  3. Mar 25, 2008 #2


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    Yes you would solve for the mass of nitrogen since the energy from the copper will be the energy used to change the nitrogen from liquid to solid.
  4. Mar 25, 2008 #3


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    Thanks alot Kurdt :smile:
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