- #1

alpha_wolf

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Hi.

I need to calculate the entropy of some material at a certain temperature given the Cp at each phase and the entalpy change and temperature at phase transitions. I'm supposed to use thermodynamic considerations (i.e. statistical definition of entropy is not applicable/allowed).

I know how to translate the entalpy change to entropy change, so I was thinking of doing an itegral of (Cp/T)dT across each of the temperature ranges, and then summing up the intergals and the entropy changes of the phase transitions. The problem is that the first integral is from 0K to the first transition temperature, so it gives ln(0) as one of the components. This is obviously not usable... I suppose this is because the polynomial definition for Cp breaks down at extremely low temperatures.

How can I overcome the problem? Maybe assume the entropy change near absolute zero is negligible and integrate from 0.1K instead of 0K? The numbers don't quite agree with that assumption...

I need to calculate the entropy of some material at a certain temperature given the Cp at each phase and the entalpy change and temperature at phase transitions. I'm supposed to use thermodynamic considerations (i.e. statistical definition of entropy is not applicable/allowed).

I know how to translate the entalpy change to entropy change, so I was thinking of doing an itegral of (Cp/T)dT across each of the temperature ranges, and then summing up the intergals and the entropy changes of the phase transitions. The problem is that the first integral is from 0K to the first transition temperature, so it gives ln(0) as one of the components. This is obviously not usable... I suppose this is because the polynomial definition for Cp breaks down at extremely low temperatures.

How can I overcome the problem? Maybe assume the entropy change near absolute zero is negligible and integrate from 0.1K instead of 0K? The numbers don't quite agree with that assumption...

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