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Homework Help: Entropy problem (i think)

  1. Jan 3, 2010 #1
    Hi, i just want to check my reasoning on this problem.

    A working substance is taken around a closed cycle that involves performing some external work. It absorbes heat Q1 = 1000J from a resevoir at T1 = 1000K, and heat Q2 = 2000J from a resevoir at T2 =2000K. The only other exchange of heat is with a resevoir at T3 = 300K.
    What is the minimum heat that must have been transferred from the substance to the resevoir at T3 ( explain your reasoning)?

    Now i think the minimum heat is 600J, as the entropy change of the system must be >= 0, and we must have heat rejection otherwise we'd violate the 2nd law. Is this ok?
  2. jcsd
  3. Jan 3, 2010 #2


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    Hi Bigfoots mum, welcome to PF. Your reasoning looks good to me.
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