In this section you will learn of an important relationship between the equilibrium constant for a reaction and the change in Gibbs free energy for the reaction.
The reaction free energy is the change in G due to the displacement (or advancement) of the reaction and is given by the symbol G. If the reaction is at equilibrium G will be zero for at equilibrium there is no further net advancement of the reaction. For the reaction
aA + bB cC + dD
the reaction quotient (Chapter 16) is Q = [C]c[D]d/([A]a[B]b) and the relationship between the reaction free energy, the reaction quotient and the Gosystem is
G = [delta]Go + RTlnQ
At equilibrium, 0 = Go + RTlnKc where Kc is the value of the reaction quotient at equilibrium and is the thermodynamic equilibrium constant:
K = [C]c[D]d/([A]a[B]b)equil
We then have that Go = -RTlnKc which is a very useful equation. From this equation we can use values of thermodynamic data to calculate equilibrium constants. If the reactants and products are gases the Q will be expressed in terms of the partial pressures of the gases rather than the concentrations and the corresponding equilibrium constant would be written as Kp.
In section 16.3 we determined that
Web Author: Dr. Leon L. Combs
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