Find the difference in entropy between a cup of water and a cup of ice

AI Thread Summary
The discussion revolves around calculating the difference in entropy between a cup of water and a cup of ice under two scenarios: both at 0°C and ice at 0°C while water is at 20°C. It is clarified that water at 0°C is not necessarily ice, as there is energy change involved in the phase transition. The participants express confusion over using the heat equation Q=cmΔT for entropy calculations, particularly when dealing with zero temperature. There is a suggestion that the problem may involve finding the change in entropy when mixing the two substances. The importance of using the correct temperature units in entropy calculations is also emphasized to avoid errors.
erin88
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Find the difference in entropy between a cup of water and a cup of ice for each of these cases:
1. both are at T=0C
2. ice is at T=0C water is at 20C

~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
If the "water" is at 0C then it is ice right? and the difference in entropy is 0 correct?

For the second part... do you think I am supposed to find the Q for each one? since the equation for Q is Q=cmT I don't think this would make sense because the equation for entropy (S) is S=Q/T. For ice it would be 0/0 and you can't do that...

Do you think maybe he's asking for the change in entropy if you mix the two together?

Thanks.

~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
EDIT

I just remembered the equation is Q=cmdeltaT

So this must mean that he does want to know the change of entropy in the system if you mix the two together??
 
Last edited:
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erin88 said:
Find the difference in entropy between a cup of water and a cup of ice for each of these cases:
1. both are at T=0C
2. ice is at T=0C water is at 20C

~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
If the "water" is at 0C then it is ice right? and the difference in entropy is 0 correct?

For the second part... do you think I am supposed to find the Q for each one? since the equation for Q is Q=cmT I don't think this would make sense because the equation for entropy (S) is S=Q/T. For ice it would be 0/0 and you can't do that...

Do you think maybe he's asking for the change in entropy if you mix the two together?

Thanks.

~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
EDIT

I just remembered the equation is Q=cmdeltaT

So this must mean that he does want to know the change of entropy in the system if you mix the two together??

First I'll address the conceptual problem:
Ice is not simply water at T=0C, there is change in energy associated with melting/freezing. I think this might give you a bit of a start on the first part.

The next issue to address:
We have Q = S T
The first question that crosses my mind is what are the units on T?
Should it be K? C? F? R? I think the answer to this question will relieve your divide by zero error.
 
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