1. Limited time only! Sign up for a free 30min personal tutor trial with Chegg Tutors
    Dismiss Notice
Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Homework Help: Problem on entropy change and specific heat capacity

  1. May 14, 2014 #1
    Calculate the change in entropy of the Universe as a result of the following
    (a) A copper block of mass 0.4kg and thermal capacity 150JK-1 at 100◦C is
    placed in a lake at 10◦C.

    dS=dQ/T dQ=mCdT

    Tried simply combining these equations and integrating to find change of entropy of block. Knowing that final temperature of the block will be approximately the initial temperature of the lake. So we get
    mc[ln(T)] between boundaries of T1 and T2. However, this thermal capacity does not have the standard units for c, which is JK-1Kg-1, so I am questioning my whole approach. Assuming this is just some typo perhaps and I do indeed do this, I am not sure on how to find the universal entropy change. Any help would be greatly appreciated.
    Many thanks in advance.
  2. jcsd
  3. May 14, 2014 #2
    It's an obvious typo, so, what is the change in entropy of the block?
    How much heat is transferred from the block to the lake?
    At what temperature does the lake receive this heat?
    What is the change in entropy of the lake?
    What is the total change in entropy for the block plus lake?

  4. May 15, 2014 #3

    rude man

    User Avatar
    Homework Helper
    Gold Member

    Does it have to be a typo? The 0.4kg could just be a red herring.
  5. May 15, 2014 #4
    True. Who knows?

  6. May 21, 2014 #5
    It turns out It wasn't a typo, the C here was the heat transfer per unit temperature (multiple of C and M), something I was not familiar with. As a result the the question becomes much simpler, just being the sum of the two entropy change (block and lake)
    Your help was much appreciated :)
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook

Have something to add?
Draft saved Draft deleted