![]() Transcribed image text: Which substance in each of the following pairs would you expect to. ![]() Randomness we can get the idea of that by the molar mass of molecule, more the molecular mass more is the randomness. Unfortunately, that source isn't readily viewable online (all I found was what appears to be a German version, at Berichte der Bunsengesellschaft für physikalische Chemie 1990, 94 (1), 93–93 (It's behind a paywall.) But if you could get your hands on it (interlibrary loan, say), it should contain a detailed description of how the values were actually calculated.įWIW, here's a link showing how standard molar entropies might be calculated (but I don't know if the procedure described here is what is used to determine the official CODATA values): Standard Molar Entropy of Solid Aluminum Oxide, Comments to Tandy Grubbs, Stetson University ( via the Internet Archive).Įssentially, it mentions using the Debye extrapolation I mentioned in an earlier comment up to $\approx\pu$, the fact that the system is locked into only one microstate (even if it's not a perfect crystal) gives it zero entropy. Entropy -depends on the randomness of molecules. entropies of some main group elements and the conventional standard molar. A., CODATA Key Values for Thermodynamics, Hemisphere Publishing Corp., New York, 1989. The Table 2.13 Standard molar bromate ( V ) ion has intermediate properties. Here's a link to the official CODATA site showing the values:Ĭox, J. ![]() Column III equation 3.86 with procedure of Holland (1989). Column I simple summation of standard molar entropies of constituent oxides. Not quite an answer, but too long for a comment: Table 3.6 Comparison of predictive capacities of various equations in estimating standard molar entropy T 298.15 K, P 1 bar). What is the precise definition (preferably with reference) of standard molar entropy? Most of the following issues will be covered by the exact definition, but to be more elaborate, these immediately come to my mind: what exactly is the standard state for each element? Do all elements form a perfect crystal at 0 K, and how can we prove this? Should I think of the third law (zero entropy at zero kelvin) as being a definition that sets an otherwise arbitrary baseline, or can it be proven that the quantum mechanical von Neumann entropy really is zero for pure elements at 0 K?Īn internet search turned up plenty of information about the values of standard molar entropy for various compounds and how to use them, but I wasn't able to find a resource with a detailed description of its definition. However, I'm not even sure that's exactly correct, and there are a lot of details that need to be filled in if it is right. Then, for the compound of interest, calculate and/or measure the entropy difference between the compound and its constituent elements at 0 K. My recollection from a long time ago is that it goes roughly like this:įor each element, assume that its entropy goes to zero at 0 kelvin when it's in some standard state I understand what the standard molar entropy is, and how to use it in calculations, but I'm interested in understanding exactly how it's defined and measured.
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