December 07, 2022, 01:23:44 AM
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Topic: Standard Molar Enthalpies of Chemicals  (Read 386 times)

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Offline jasian

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Standard Molar Enthalpies of Chemicals
« on: October 23, 2022, 09:45:33 PM »
Where can I see the standard, accepted values for molar enthalpies of certain chemicals? In this case, sodium acetate and sodium sulfate. I can't find them anywhere, for some reason.

Offline Aldebaran

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Re: Standard Molar Enthalpies of Chemicals
« Reply #1 on: October 24, 2022, 03:08:11 AM »
I Googled both these and found them straight away. Wikipedia was the source which is usually fairly reliable . There were also several data tables listing lots of other compounds

Offline Enthalpy

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Re: Standard Molar Enthalpies of Chemicals
« Reply #2 on: October 24, 2022, 07:01:47 AM »
Which enthalpy do you mean? Fusion, evaporation, formation, combustion, other?

For the enthalpies of formation, tables exist. Huge but missing the one compound you need usually. The CRC Handbook of Chemistry and Physics has such a table. The Janaf table is known for flame purposes. They exist as pdf on the Web, possibly infringing copyrights. The CHC Hdbk of Chem&Phys is available at many university libraries.

Beware most values on the Web are only estimates by software. These estimates use to be very wrong, completely useless. Values older than 1970 or 1960 are more credible. Compare also the values in a table: if a 2-methyl equals a 3-methyl it's a computer scam. And for the heats of formation, always check if the substance is liquid, gaseous, solid, in solution, etc. If the state isn't told it's because the author doesn't even know the difference and pasted a value from a software.

I don't really grasp what an "accepted value" should be...
* If values don't contradict an other, it's because only one measurement has been done. More so in thermochemistry.
* You decide what you believe. Believing something because others do is not science.

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