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Find initial temp. of alcohol when copper and aluminum are added

  1. Sep 8, 2012 #1
    *Messed up title, should have been find initial temp of copper*

    1. The problem statement, all variables and given/known data

    8.00 g of aluminum at 200 °C and 18.0 g of copper are dropped into 50.0 cm3 of ethyl alcohol at 15 °C. The temperature quickly comes to 26.0 °C. What was the initial temperature of the copper?

    Density of ethyl alcohol = .789 g/ml

    mass of ethyl alcohol = 39.45 g, .03495 kg

    mass of copper = .018 kg

    mass of aluminum = .008 kg

    Tf = 299 K

    Ti, alum = 473 K

    Ti, eth = 288 K

    c for aluminum = 900 J/kg*k

    c for ethyl alcohol = 2400 J/kg*k

    c for copper = 385 J/kg*k

    2. Relevant equations

    Qa + Qc + Qe = macaΔT + meceΔT + mcccΔT = 0

    3. The attempt at a solution


    Qa + Qc + Qe = macaΔT + meceΔT + mcccΔT = 0

    =(.008)(900)(-174) + (.03945)(2400)(11) + (.018)(385)(299-Ti) = 0

    Ti = 268.51 K or -4.5 °C

    That's what I did, but it says not quite and tells to check for rounding errors. However, I didn't round anything until the very end, so I'm not quite sure where I went wrong. I also tried -4.494 but that was wrong too.
     
  2. jcsd
  3. Sep 8, 2012 #2

    TSny

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    Could this be the error?
     
  4. Sep 9, 2012 #3
    Well, I feel stupid now. thanks.
     
  5. Sep 9, 2012 #4

    TSny

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    Gold Member

    No need to worry. We all make slips like that. Hope it works out now.
     
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