## Third Law Clarification/ Practice Midterm Question 3E

Boltzmann Equation for Entropy: $S = k_{B} \ln W$

Alexia Joseph 2B
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### Third Law Clarification/ Practice Midterm Question 3E

Why is it false that molecules at exactly 0 degrees Kelvin have no entropy? In theory, isn't the third law of thermodynamics that the entropy of a perfect crystal is zero when the temperature is equal to absolute zero (0 K)?

Sarah Rutzick 1L
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### Re: Third Law Clarification/ Practice Midterm Question 3E

Its true that the entropy of a perfect crystal is 0 at T=0 K. This is because perfect crystals only have one micro state, so using Boltzmann's equation and plugging in 1 for W, you get zero. However, most substances are not perfect crystals, so for these substances entropy is not 0 at T=0 K.

Chem_Mod
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### Re: Third Law Clarification/ Practice Midterm Question 3E

To clarify further, since the statement did not specify a perfectly ordered material, the statement is false. Otherwise it would have been true. Important concept is that the material must be at 0K AND perfectly ordered.

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