Gibbs Free Energy and maximum work

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Discussion Overview

The discussion revolves around the concept of Gibbs free energy, particularly its interpretation as the maximum amount of non-expansion work that can be extracted from a closed system. Participants explore the conditions under which this maximum work is achieved, specifically focusing on isothermal processes and the relationship between Gibbs free energy, entropy, and internal energy.

Discussion Character

  • Technical explanation
  • Conceptual clarification
  • Debate/contested

Main Points Raised

  • Some participants assert that Gibbs free energy represents the maximum work obtainable only in a completely reversible and isothermal process.
  • There is a discussion about the term TS in the context of Gibbs free energy, with questions raised regarding the nature of this energy and its source if not derived from the internal energy of the system.
  • One participant emphasizes that the change in Gibbs free energy is linked to the heat released by the system, suggesting that this heat must be accounted for when calculating work.
  • Another participant proposes that the term TΔS is part of the change in internal energy, leading to a discussion on how this relates to the useful work derived from internal energy.
  • A later post questions the physical meaning of Gibbs free energy in chemical reactions, particularly in terms of spontaneity and the work done by chemical reactions, suggesting a potential link to chemical bonding energy.

Areas of Agreement / Disagreement

Participants generally agree on the relationship between Gibbs free energy and maximum work in isothermal processes, but there are differing views on the implications of TS energy and its physical meaning in chemical reactions. The discussion remains unresolved regarding the broader implications of Gibbs free energy beyond spontaneity.

Contextual Notes

Limitations include assumptions about the reversibility of processes and the specific conditions under which Gibbs free energy applies. The discussion also reflects uncertainty regarding the physical interpretation of Gibbs free energy in the context of chemical reactions.

tonyjk
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Hello,
The Gibbs free energy is the maximum amount of non-expansion work that can be extracted from a closed system; this maximum can be attained only in a completely reversible process. This maximum work is equal to H-TS. My question is this TS energy is what kind of energy? and from where it will come if it is not from the internal energy of the system?

Thank you
 
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The change of G is only the maximum work if the process is isothermal. Then ##\Delta TS=T\Delta S## and, as the process is reversible, the change of entropy of the system has to equal the change of entropy of the environment, which is ## \Delta S = Q/T##. So basically you are substracting the heat released by the system from the change in energy to get the work, only.
 
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DrDu said:
The change of G is only the maximum work if the process is isothermal. Then ##\Delta TS=T\Delta S## and, as the process is reversible, the change of entropy of the system has to equal the change of entropy of the environment, which is ## \Delta S = Q/T##. So basically you are substracting the heat released by the system from the change in energy to get the work, only.
But the change of internal energy is it also the heat generated by the system?
 
DrDu said:
The change of G is only the maximum work if the process is isothermal. Then ##\Delta TS=T\Delta S## and, as the process is reversible, the change of entropy of the system has to equal the change of entropy of the environment, which is ## \Delta S = Q/T##. So basically you are substracting the heat released by the system from the change in energy to get the work, only.
Ah you mean ##T\Delta S## is part of change of internal energy of the system thus subtracting to ##\Delta H## you will get the useful work from internal energy right?
 
tonyjk said:
Ah you mean ##T\Delta S## is part of change of internal energy of the system thus subtracting to ##\Delta H## you will get the useful work from internal energy right?
Yes, exactly.
 
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Just a last question,

Gibbs free energy used in chemical reactions; excluding oxydo-reduction reaction, is only used to know if the reaction is spontaneous or not and does not have any physical meaning? If It has, what is work done by a chemical reaction? Is it related to potential energy due to chemical bonding?

Thank you
 
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