Re: pinhole Entropy question

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From: NFetter@aol.com
Date: Thu Feb 17 2005 - 19:35:51 PST 

From: NFetter@aol.com
Message-ID: <8b.2158c4bd.2f46bc97@aol.com>
Date: Thu, 17 Feb 2005 22:35:51 EST
Subject: Re: pinhole Entropy question

Hi Geoff,
By standard entropy, I assume you mean the absolute entropy at 25 degrees C
and 1 atm pressure. For any substance the absolute entropy is the only property
of state that can be measured. (Enthalpy and Gibbs free energy cannot). The
absolute entropy is determined from heat capacity measurements starting at 0K
and enthalpys for changes of state. For example, the molar heat capacity of
crystalline sulfur can be measured form near 0K to the melting point, then
enthalpy of fusion is added, and finally, the heat capacity to 25C is measured and
added. The total of all these heat measurements is the standard molar absolute
entropy. This number is always positive. If the standard entropy is given a
value of zero, this is an arbitrary assignment for the sake of measuring entropy
changes. The standard enthalpy of the elements is given an assigned value of
zero in order to make enthalpy changes easier to measure. Any help?
Neil Fetter

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