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Thermo - Ice melting

  1. Feb 28, 2010 #1
    1. The problem statement, all variables and given/known data
    An insulated beaker with negligible mass contains liquid water with a mass of 0.325 \rm{kg} and a temperature of 69.9 C.

    How much ice at a temperature of -15.0 C must be dropped into the water so that the final temperature of the system will be 39.0 C?
    Take the specific heat of liquid water to be 4190 , the specific heat of ice to be 2100 , and the heat of fusion for water to be 334


    2. Relevant equations
    Q = mcT
    Q = mL


    3. The attempt at a solution
    m = mass of ice

    Melt Ice = 334 * m
    Heat Ice = 2100 * (0--15) * m
    Heat ice water = m*4190 * (39-0)

    Cool Water = 0.325 * 4190 (39-69.9) = 42078.075

    Solve for m
    42078.075 = 334 * m + 2100 * (0--15) * m + m*4190 * (39-0)

    m= 0.2155 kg


    Found another equation and used it and got the same answer.... not sure where I am going wrong.

    Mice = Mwater * Cwater (Tf - Twater)/(Cice * Tice -Lf - Cwater * Tf)

    [0.325 * 4190 * (39-69.9)] / (2100 * -15 -334-4190*39) =0.2155kg
     
    Last edited: Feb 28, 2010
  2. jcsd
  3. Feb 28, 2010 #2
    Anyone got an idea whats up? When I plugged in the answer it told me "Dont forget the energy needed to melt the ice. !?!?!?!
     
  4. Feb 28, 2010 #3
    The heat of fusion if Ice is actually 334 KJ/kg or 334*10^3 J/kg
     
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