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Homework Help: Thermodynamics: entropy

  1. Nov 2, 2007 #1
    1. The problem statement, all variables and given/known data

    Heat leaks out of a house at the rate of [tex]2.5\times{10^4} \frac{kcal}{h}[/tex]. The temperature inside the house is 21°C and the temperature outside the house is -5°C. At what rate does this process produce entropy.


    2. Relevant equations

    [tex]S(A)-S(A_0)=-\frac{\Delta{Q}}{T_1}+\frac{\Delta{Q}}{T_2}=\Delta{Q}\times{(\frac{1}{T_2}-\frac{1}{T_1})}[/tex]


    3. The attempt at a solution

    Heat flows from the high temp res to the low temp res at a rate of [tex]2.5\times{10^4} \frac{kcal}{h} = 6944.4 \frac{cal}{s} = \Delta{Q}[/tex].

    [tex]T_1=21°C=294.15K[/tex]
    [tex]T_1=-5°C=268.15K[/tex]

    Plugging and chugging I get: [tex]2.29 \frac{cal}{K\times{s}}[/tex], which is wrong.

    The answer in the back of the book is [tex]8.2\times{10^3}\frac{cal}{K\times{s}}[/tex].
     
  2. jcsd
  3. Nov 3, 2007 #2

    hage567

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    Homework Helper

    If you leave your answer in cal/(K x h), you get the book's answer. Maybe they made a mistake?
     
  4. Nov 4, 2007 #3
    Now I feel stupid for overlooking a such a trivial detail as unit conversions.
     
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