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Bandwidth Hog

Joined: 23 Jan 2004
Posts: 2247

Posted: 25 Apr 2010 04:09:23 pm    Post subject:

I'm having a tough time understanding Entropy. The question I'm having difficulty with is:

10 kg of water at 0 C is mixed with 10 kg of water at 100 C. The change in entropy (in cal/K) of the system is? Is there a general equation to this?

Edit: The equation I found was the integration of T1 to T2 dQr/T. Now I'm just a little confused on dQ.

Last edited by Guest on 25 Apr 2010 04:36:39 pm; edited 1 time in total
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μολών λαβέ

Active Member

Joined: 27 Mar 2005
Posts: 569

Posted: 25 Apr 2010 07:05:41 pm    Post subject:

Well, the trick of course is how you'd express dQ in terms of dT. Smile You might find the heat capacity of water (for which phase(s) of water, you'll have to figure out, but what is so special about those given temperatures?) to be a useful quantity in your calculations.

However, it is the change in entropy that is being asked of you, so think about whether you should be integrating or not. (What is a differential, anyway?)

Finally, don't forget that all temperatures be in absolute units!

Hope this helps.


P.s. Bonus exercise: what is the final temperature of your mix?
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