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Chem 2 - Free Energy and the Equilbrium Constant K VIII

Chem 2 - Free Energy and the Equilbrium Constant K VIII

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Chem 2 - Free Energy and the Equilbrium Constant K VIII

  1. 1. Free Energy and the Equilibrium Constant K (Pt 8) By Shawn P. Shields, Ph.D. This work is licensed by Shawn P. Shields-Maxwell under a Creative Commons Attribution-NonCommercial-ShareAlike 4.0 International License.
  2. 2. G and the Equilibrium Constant K Without derivation, the relationship between the Gibbs free energy and the equilibrium constant K is ∆G° = −RT lnK
  3. 3. G and the Equilibrium Constant K We can obtain the value of the equilibrium constant K using G K = 𝑒− ∆G° RT
  4. 4. G and the Equilibrium Constant K ∆G° = −RT lnK When G < 0, the value for K > 1 (products are favored) When G > 0, the value for K < 1 (reactants are favored) When G = 0, the value for K = 1 and the reaction is at equilibrium.
  5. 5. G and the Equilibrium Constant K ∆G° = −RT lnK Recall that G means the reaction is under standard conditions. (1 atm pressure for gases and 1 M concentration for solutions)
  6. 6. G and the Equilibrium Constant K ∆G° = −RT lnK There is only one value for G for a given reaction, and the reaction must have gone to completion. What if there is a mixture of reactants and products (i.e., the reaction didn’t go to completion)?
  7. 7. The Difference Between G and G G always has the same value for a particular reaction and is calculated using tabulated data. G is the actual free energy of the reaction at a given composition. What does this mean?
  8. 8. The Difference Between G and G G has a different value for each composition. G is minimized at equilibrium. “dGdGo" from http://www.chem1.com/acad/webtext/the rmeq/TE4.html
  9. 9. The Difference Between G and G Since G is the actual free energy of the reaction at a given composition, it changes over the course of the reaction. G can be calculated for non-standard conditions at any point in the reaction.
  10. 10. Free Energy for Non-Standard Conditions (G) Recall: ∆G° = −RT lnK For non-standard conditions, the free energy change is ∆G = ∆G° + RT ln Q Where Q is the reaction quotient.
  11. 11. IMPORTANT! G versus G G is for std conditions and always has the same value for a particular reaction. G is the actual free energy of the reaction at a given composition and changes over the course of the reaction (non-standard conditions).
  12. 12. Example Problems will be posted separately 

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