How is Gibbs Free Energy Calculated?

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Discussion Overview

The discussion revolves around the calculation of Gibbs Free Energy, exploring different methods and their applicability based on available data. Participants examine both the general formula involving enthalpy and entropy, as well as a method based on the difference between the Gibbs energies of products and reactants.

Discussion Character

  • Technical explanation, Conceptual clarification, Debate/contested

Main Points Raised

  • One participant questions whether to use the formula ΔG = ΔH – T * ΔS or to calculate ΔG as the difference between products and reactants.
  • Another participant suggests that either method can be used, depending on the data available.
  • A third participant argues that using ΔG = ΔH – T * ΔS is more general and applicable at any specified temperature, while calculating ΔG as G_products – G_reactants is limited to the temperature for which the Gibbs values are provided.
  • This participant also raises a scenario involving non-spontaneous reactions and the need to determine the temperature required for spontaneity, indicating that the traditional method may be necessary in such cases.
  • A fourth participant provides a definition of the Gibbs Free Energy equation, explaining its components: G for Gibbs Free Energy, H for enthalpy, T for absolute temperature, and S for entropy.

Areas of Agreement / Disagreement

Participants express differing views on the methods for calculating Gibbs Free Energy, indicating that multiple competing approaches exist without a clear consensus on which is preferable in all situations.

Contextual Notes

Some limitations are noted regarding the applicability of the Gibbs Free Energy table under standard conditions and the implications for non-spontaneous reactions.

afcwestwarrior
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do i have to use this formula Delta G=delta h- t*delta s

or could i calculate it like i calculate delta h, products - reactants
 
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I think you can do either way. Which way is depending on what data you've got in hand
 
Calculating the change in the Gibbs Free Energy as,
ΔG = ΔH – T * ΔS
Is a more general way to do it since this will be true for any specified temperature, T.

You could calculate it as,
ΔG = G_products – G_reactants
But this will only be valid for the temperature which your table has its G values calculated in. You might have access to a table of standard G of formation, but this would only be true under standard conditions.
What if you had a non-spontaneous reaction (under standard conditions) and you wanted to find out the temperature you needed to raise it to in order to make it spontaneous? To do this, you would have to calculate it the old fashion way without the Free Energy table.
 
Gibbs free energy equation is a thermodynamic equation that is used to calculate the change in the Gibbs free energy of a system. The Gibbs Free Energy equation is written as G=H-TS Where G is the Gibbs Free Energy, H is the enthalpy, T is the absolute temperature and S is the entropy.
 

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