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Topic: What do values of enthalpy and free energy mean compared to each other?  (Read 2789 times)

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Offline LogicX

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for the same reaction?

For example, if you have the reaction 6A4--> 4A6 and you calculate that free energy is higher (more positive) than enthalpy for this reaction, how would you reason why free energy is larger?  Is it because free energy takes into account entropy and thus is more unfavorable than enthalpy?

Offline XGen

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I am not sure what you are asking.

Do you know the relationship between enthalpy, entropy, and Gibb's free energy?

Offline LogicX

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Yeah, G= H-TS.

The question is to explain why dG (which was determined computationally) is larger than dH (also determined computationally) based on the above reaction.  Entropy was also determined computationally.  I mean, I can explain it mathematically I guess, but not conceptually.
« Last Edit: March 23, 2012, 12:38:44 AM by LogicX »

Offline juanrga

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    • juanrga - sharing unified knowledge in pure and applied sciences
for the same reaction?

For example, if you have the reaction 6A4--> 4A6 and you calculate that free energy is higher (more positive) than enthalpy for this reaction, how would you reason why free energy is larger?  Is it because free energy takes into account entropy and thus is more unfavorable than enthalpy?

Assuming constant temperature :delta: G = :delta: H - T :delta: S

If :delta: S < 0 for a given reaction, then :delta: G > :delta: H

At the left of your reaction you have 6 units of A4, at the right you have 4 units of A6. Entropy must be low at the right because (i) you have less units (entropy is extensive) and (ii) each unit of A6 is more constrained (has more bonds) that each unit of A4 and has less accessible states.
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