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Is the minimum Gibbs free energy the same for every material?

  1. May 19, 2016 #1
    We were learning about the change in free energy in class, but I was wondering since the Gibbs free energy decreases as a system becomes more stable, is the minimum absolute free energy for a material the same for every material, or can other materials be more stable than others?
  2. jcsd
  3. May 22, 2016 #2

    James Pelezo

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    Gold Member

    Hmmmm, interesting question... I'd say 'yes' if your defense is based upon ΔG = ΔGo + RTlnQeq. The ΔG in this equation defines a system under 'non-standard' conditions. When ΔG ≠ 0 the system is dynamic in nature and its free energy can change based upon whether or not the system is spontaneous or non-spontaneous in nature, but still indicates the system of interest is tending always to the most stable condition of disorder. See attached figure. This most 'stable' condition occurs when ΔG = 0 the the system is said to be at its minimum free energy and is defined by ΔG = 0 = ΔGo + RTlnQeq. This is the minimum ΔG that can occur for any system. However, the equation also shows that at ΔG = 0 => ΔGo = -RTlnKeq = ∑n⋅ΔGfo(Products) - ∑n⋅ΔGfo(Reactants). This implies that different substances (reacting systems) have different changes in 'standard' free energies based upon the chemical and physical properties of the system of interest. Of course the more negative 'standard' free energy would be the more stable system but outside the standard state conditions, all systems tend to ΔG = 0 ...This is a double edged sword depending on how you define the free energy change of a system. I welcome any and all rebuttals to this point of view. It is an interesting issue. Thanks all. Doc
    http://blob:https%3A//www.physicsforums.com/578ec8ce-71b9-44ed-bbfa-8a1bdf1f227b upload_2016-5-22_22-57-20.png
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