18.5 Gibbs Free Energy and the Equilibrium Constant | General Chemistry

Chad concludes the chapter on Thermodynamics with a lesson on the relationship between Gibbs Free Energy and the Equilibrium Constant. The lesson begins with a discussion of the mathematical relationship between the nonstandard free energy change, the standard free energy change, and the reaction quotient.
Delta G = Delta G (standard) + RTlnQ
An example calculation of the change in Gibbs free energy under nonstandard conditions is performed. This equation also allows us to draw the following three conclusions:
1. If Q is less than K, then Delta G is negative.
2. If Q is greater than K, then Delta G is positive.
3. If Q is equal to K, then Delta G = 0.

The relationship between the standard Gibbs free energy change and the equilibrium constant is then derived from this equation.

Delta G (standard) = -RTlnK

This equation can be used to calculate the standard Gibbs free energy change at a particular temperature from the equilibrium constant, or to calculate the equilibrium constant at a particular temperature from the standard Gibbs free energy change. An example calculation of the latter is performed.

Finally, a graphical representation of Gibbs free energy vs reaction progress is presented. A number of thermodynamic quantities are identified on the graph including the standard Gibbs free energy change, nonstandard delta G, the equilibrium constant and the reaction quotient.

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00:00 Lesson Introduction
00:25 Nonstandard Gibbs Free Energy Change
07:47 Delta G = -RTlnK
18:28 Graph of Gibbs Free Energy vs Reaction Progress

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