Free Energy and the Equilibrium Constant K (Pt 8)By Shawn P. Shields, Ph.D.

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G and the Equilibrium Constant K

Without derivation, the relationship between the Gibbs free energy and the equilibrium constant K is

G and the Equilibrium Constant K

We can obtain the value of the equilibrium constant K using G

G and the Equilibrium Constant K

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.

G and the Equilibrium Constant K

Recall that G means the reaction is under standard conditions.(1 atm pressure for gases and 1 M concentration for solutions)

G and the Equilibrium Constant K

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)?

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?

The Difference Between G and GG has a different value for each composition.G is minimized at equilibrium.

“dGdGo" from http://www.chem1.com/acad/webtext/thermeq/TE4.html

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.

Free Energy for Non-Standard Conditions (G)

Recall: For non-standard conditions, the free energy change is

Where Q is the reaction quotient.

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).

Example Problems will be posted separately