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Topic: Calculating Gibbs Free Energy  (Read 2573 times)

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Offline bg93

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Calculating Gibbs Free Energy
« on: September 16, 2013, 10:57:32 AM »
My chemical engineering class has assigned us a pretty intense problem that we're getting into groups to solve during the course of the week. This is one of the first hurdles to a solution.

Basically, we need to calculated the Gibbs Free Energy (delta G) for a couple reactions, the catch is that they will have to be on a function of temperature. Previously, we could use the NIST chemistry webbook, which had a function and a set of constants that we could plug in to get the enthalpy and entropy at any temperature, but for the compounds in this problem the constants have not been solved for. What we ended up doing was finding a table of values (specific heat at a temperature), calculating a cubic regression, and integrating that equation. I could settle for this, but it wasn't super accurate, I can't think of anything better. Worse is there's no data points I could use to create a function of entropy for some compounds.

I'm looking for the delta G of 1,3-butadiyne, benzene, 1-Buten-3-yne, and styrene. I (and my group) would really appreciate it if someone hear could point us in the right direction, we can't really move on without this.

Offline curiouscat

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Re: Calculating Gibbs Free Energy
« Reply #1 on: September 16, 2013, 11:04:01 AM »
I could settle for this, but it wasn't super accurate, I can't think of anything better.

Why do you think it wasn't accurate? Most Cp equations are fits of one sort or another.

Offline bg93

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Re: Calculating Gibbs Free Energy
« Reply #2 on: September 16, 2013, 04:46:37 PM »
Just because the standard enthalpy at 298K was a ways off from what it should be.

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